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Triazine-Substituted Zinc Porphyrin as an Electron Transport Interfacial Material for Efficiency Enhancement and Degradation Retardation in Planar Perovskite Solar Cells Nikolaos Balis, Apostolis Verykios, Anastasia Soultati, Vassilios Constantoudis, Michael Papadakis, Fotis Kournoutas, Charalampos Drivas, Maria-Christina Skoulikidou, Spyros Gardelis, Mihalis Fakis, Stella Kennou, Athanassios G Kontos, Athanassios G. Coutsolelos, Polycarpos Falaras, and Maria Vasilopoulou ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00447 • Publication Date (Web): 21 Jun 2018 Downloaded from http://pubs.acs.org on June 21, 2018

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ACS Applied Energy Materials

Triazine-Substituted Zinc Porphyrin as an Electron Transport Interfacial Material for Efficiency Enhancement and Degradation Retardation in Planar Perovskite Solar Cells Nikolaos Balis,† Apostolis Verykios,† Anastasia Soultati,† Vassilios Constantoudis, † Michael Papadakis,‡ Fotis Kournoutas,# Charalampos Drivas,ǁ Maria-Christina Skoulikidou,†,⌡ Spyros Gardelis,⌡ Mihalis Fakis,# Stella Kennou,ǁ Athanassios G. Kontos,† Athanassios G. Coutsolelos,‡ ,* Polycarpos Falaras,† ,* Maria Vasilopoulou†,*

†

Institute of Nanoscience and Nanotechnology, National Center for Scientific Research

Demokritos, Agia Paraskevi, 15310 Athens, Greece ‡

Department of Chemistry, University of Crete, Laboratory of Bioinorganic Chemistry,

Voutes Campus, Heraklion 70013, Crete, Greece #

ǁ

Department of Physics, University of Patras, 26504 Patras, Greece

Department of Chemical Engineering, University of Patras, 26504 Patras, Greece

⌡

Solid State Physics Section, Physics Department, National and Kapodistrian University of

Athens, Panepistimioupolis, 15784 Zografos, Athens, Greece

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*email: [email protected] (M. Vasilopoulou), [email protected] (P. Falaras), [email protected] (A. Coutsolelos).

Keywords : Perovskite solar cells, planar structure, porphyrin, titanium dioxide, electron transport interlayer, stability.

Abstract Motivated by the excellent electron transfer capability of porphyrin molecules in natural photosynthesis, we introduce here the first application of a porphyrin compound to improve the performance of planar perovskite solar cells. The insertion of a thin layer consisting of a triazine-substituted Zn porphyrin between the TiO2 electron transport layer and the CH3NH3PbI3 perovskite film significantly augmented electron transfer towards TiO2 while also sufficiently improved the morphology of the perovskite film. The devices employing porphyrin-modified TiO2 exhibited a significant increase in the short-circuit current densities and a small increase in the fill factor. As a result, they delivered a maximum power conversion efficiency (PCE) of 16.87% (average 14.33%) which represents a 12% enhancement compared to 15.01% (average 12.53%) of the reference cell. Moreover, the porphyrin-modified cells exhibited improved hysteretic behaviour and a higher stabilized power output of 14.40% compared to 10.70% of the reference devices. Importantly, nonencapsulated perovskite solar cells embedding a thin porphyrin interlayer showed an elongated lifetime retaining 86% of the initial PCE after 200 hours while the reference devices exhibited higher efficiency loss due to faster decomposition of CH3NH3PbI3 to PbI2.


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1. Introduction Photovoltaic devices allow the production of renewable energy through the direct conversion of sunlight into electricity without being harmful to the environment. Perovskite solar cells (PSCs) have recently drawn tremendous interest due to their high power conversion efficiencies (PCEs) above 22%.1-5 Besides high efficiency, they also meet all the requirements for an ideal solar cell technology such as fabrication with solution-processed low-cost methods, materials abundance and versatility in the device structure. Although first reported high efficiency perovskite solar cells adopted the mesoporous scaffold configuration,6-8 recently simpler structures with reduced complexity and manufacturing cost such as the planar configuration have been adopted. Interface engineering represents a necessary approach in optimizing the performance of planar PSCs, suffering from important losses present even in the state-of-the-art devices.9-11 To this end, inserting appropriate charge transport layers between the perovskite film and the front and back contact can play a critical role in advancing the device performance.12,13 Electron transport layer (ETL), in particular, remains a key factor influencing electron collection at the respective contact. Titanium dioxide (TiO2) is considered the dominant electron transport material in PSCs due to its excellent transmittance, superior chemical stability and proper conduction band which is compatible with those of perovskites.14-16 However, severe drawbacks of TiO2 are the poor electron transport and increased charge recombination at surface trap states.17 In addition, PSCs based on TiO2 usually exhibit large hysteresis and low stabilized power output.18 The wetting of the metal oxide is also a vital aspect since it governs the morphology/crystallization of the grown perovskite film.19-21 The implementation of suitable interfacial materials between the TiO2 ETL and the perovskite film can influence the electron extraction/collection rate, passivate surface defects and alter in



a beneficial manner the morphology of perovskite film which is self-standing in planar PSCs, thus affecting the device efficiency and improving its hysteretic behaviour. Successful interface modification of TiO2 can also improve the device environmental stability which is usually low due to the rich surface defect chemistry of TiO2.22-28 To synergistically circumvent the above issues some groups have proposed the modification of TiO2 surface with self-assembled monolayer (SAMs), fullerene derivatives and polymer:fullerene mixtures, cesium bromide, thiols or ionic liquids.29-37 Doping with several elements such as lithium (Li) and magnesium oxide (MgO) as well as chlorine-capping of TiO2 colloidal nanocrystal-based ETLs can simultaneously induce beneficial nanomorphology of the grown perovskite films and improve electron collection efficiency by mitigating interface recombination losses.38-40 Note that alternative defect-free ETLs such as tin oxide (SnO2) have been recently reported to afford better/more stable perovskite solar cells.41-43 Metallated porphyrins have been widely applied as light harvesting elements in dyesensitized,44,45 and organic solar cells.46 Recently, they have been implemented as promising hole transport materials in PSCs.47-49 However, despite the ultra-fast electron transfer capability of porphyrin assemblies their application as electron transport interlayers in photovoltaics is limited to organic solar cells recently reported by our group and others.50,51 Here we report on the first application of an appropriately substituted zinc-metallated porphyrin molecule as electron transport interfacial material inserted between the TiO2 ETL and the perovskite film to allow efficient electron transfer towards TiO2. An enhancement in the maximum PCE from 15.01% (average 12.53%) obtained in a reference cell to 16.87% (average 14.33%) upon porphyrin implementation was observed in PSCs based on methylammonium lead iodide (CH3NH3PbI3, MAPbI3) as the photoactive (perovskite) material. Moreover, improved hysteretic behaviour and increased stabilized output PCE was obtained in the porphyrin-modified cells. The reduction in surface energy of TiO2 upon 4 ACS Paragon Plus Environment

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porphyrin coating also allowed the formation of perovskite films of sufficiently improved morphology. Importantly, porphyrin employment significantly retarded the water-induced decomposition of MAPbI3 to PbI2 thus enhancing the device stability against environmental degradation elucidating its pivotal role in simultaneously improving the device efficiency and lifetime.

2. Results and discussion For the purpose of this work an appropriately substituted Zn-porphyrin molecule, in particular,

5-(4-{3,5-[glycine]-triazinyl}-aminophenyl)-10,15,20-triphenyl-porphyrin

zinc

bearing two carboxylic acid (-COOH) groups for effective anchoring into the TiO2 substrate and a triazine electron-withdrawing (acceptor) spacer to accelerate electron transfer towards TiO2,52-54 was synthesized according to a scheme presented in Figure S1 (Supporting Information). The gas-phase geometry optimized structure of ZnPtriazine(gly)2 is shown in Figure S2. It was verified that the synthesized material exhibits the characteristic absorption and emission spectra (in solution) of a Zn-metallated porphyrin (Figure S3). Then, an ultrathin porphyrin film was spin-coated on TiO2 from a 0.3 mg mL-1 methanol solution; the anchoring of porphyrin through the carboxylic acid groups into TiO2 was investigated with Fourier-transform infra-red (FTIR) spectroscopy. Figure 1a presents the 2000-900 cm-1 wavenumber region of the FTIR transmittance spectra of the as-deposited and porphyrinmodified TiO2. The transmittance profile of the as-deposited TiO2 is dominated by the H-O-H bending in the region 1600-1400 cm-1. The spectrum of the porphyrin-modified TiO2 film exhibits several additional peaks compared to the as-deposited one. Among the more intense peaks is the band at 1588 cm-1 attributed to the C=C stretching vibration (νC=C) of the phenyl rings in the porphyrin molecules. Moreover, the bands at 1500 and 1410 cm-1 are due to 5 ACS Paragon Plus Environment


asymmetric (νas) and symmetric (νs) stretching of the carboxylate anion (COO-) coming from the splitting of carboxylate groups upon binding to surface Ti centers.55,56 The C=C stretching vibration (νC=C) of carboxylic acid at 1680 cm-1 is absent from the spectrum of the porphyrinmodified TiO2.57 The FTIR spectrum of the porphyrin-modified sample suggests that ZnPtriazine(gly)2 molecule is chemically bound having both carboxylic acid groups of each molecule attached into the TiO2 substrate and not simply adsorbed on it. The exact binding mode of carboxylic acids on TiO2 can be concluded by the separation ∆νa-s between asymmetric and symmetric stretching of COO-. Band separation equal to 350-500 cm-1 corresponds to monodentate binding (ester-like linkage).55 Band separation of 150-180 cm-1 indicates bidentate bridging, and 60-100 cm-1 bidentate chelating (Figure 1b, top). In our case the ∆νa-s value is 90 cm-1 which clearly suggests a bidentate chelating binding mode (Figure 1b, bottom). Moreover, X-ray photoelectron spectroscopy (XPS) also verified the presence of ZnPtriazine(gly)2 on TiO2 surface. The Zn 2p1/2 and 2p3/2 peaks of the XPS spectra of the porphyrin-modified TiO2 sample were found at binding energies (BEs) of 1045.8 and 1022.6 eV (Figure S4a). They were attributed to Zn-N bonds with Zn in the 2+ oxidation state.58 The N1s spectrum (Figure S4b) is fitted using two peaks. The higher contribution comes from the peak at 399.2 eV which is assigned to nitrogens bonded to the zinc atom of the porphyrin ring as well as to nitrogens of the triazine spacer.59 The influence of porphyrin-modification of TiO2 on its surface electronic structure was next investigated using ultraviolet photoemission spectroscopy (UPS). Figure 1c presents the high binding energy cut-off (left), the expanded view (middle) and the near Fermi level region (right) of the UPS spectra of the as-deposited and porphyrin-modified TiO2. Both films exhibit a low work function (WF) of 4.0 eV and a valence band maximum at 3.3 eV below the Fermi level which indicates that the surface electronic structure of TiO2 is not affected by the coverage with an ultra-thin porphyrin film.


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The small peak present in the spectrum of porphyrin-modified metal oxide centered at 1.7 eV corresponds to the highest occupied molecular orbital (HOMO) of porphyrin compound.60 We next examined the morphology of the perovskite films grown on TiO2 without and with porphyrin modification using both scanning electron and atomic force microscopies (SEM and AFM respectively) (see Fig. 2a,c and Fig. S5-7). The analysis of the measurement results showed that the porphyrin modification induces more homogeneous perovskite films in both height and spatial aspects. In particular: a) AFM measurements reveal a height homogenization and smoothing of perovskite films after the addition of the porphyrin layer since the RMS (root-mean-square) of surface heights was found to decrease from 45.2 nm of the reference sample to 36.7nm in the modified film, b) the analysis of the top-down SEM images with the watershed segmentation method demonstrates the spatial homogenization of perovskite film deposited on porphyrin-modified TiO2 since the distribution of the detected grain areas of the latter is characterized by larger mean value (0.73 vs 0.55 µm2) and lower standard deviation (0.62 vs 0.76 µm2), i.e. larger and more uniform grains. The same conclusion can be reached by the calculation of the grain boundaries whose percentage over the whole image decreases in the porphyrin-modified sample (0.046 vs 0.053). The histograms of the grain areas of the porphyrin films coated on as-deposited and porphyrinmodified TiO2 are displayed in Figure 2b and 2d, respectively, while the mean areas and standard deviations of grain sizes are shown in Table S1. The improved homogeneity, larger crystal size and reduced grain boundaries amount of the perovskite film deposited on the porphyrin-modified substrate are indicative of enhanced charge generation and transport within this film. The better film forming properties of the perovskite film upon porphyrin modification of TiO2 do not result from the alteration in nanomorphology of TiO2 underlayer (as evidenced by AFM images presented in Figure S7) but rather from changes in its surface energy when coated with ZnPtriazine(gly)2 (Figure S8, Table S2). In particular, as-deposited



TiO2 exhibits lower water contact angle and higher surface energy compared to the porphyrin-modified one. As a result, the grains of the perovskite film coated on the more hydrophilic substrate are smaller due to the existence of more nucleation sites for the perovskite film growth on the un-modified substrate.61 Next, electron injection after excitation of the perovskite films was probed using steady-state photoluminesce (PL) measurements (Figure 2e). The PL spectra of MAPbI3 film deposited on TiO2 exhibits a single peak at about 780 nm with a full-width at half-maximum (FWHM) of about 46 nm.62 The PL peak of the film deposited on the modified TiO2 presents an about 3 nm blue-shift compared to the reference sample (Figure S9) which indicates a decrease in the trap density of MAPbI3 film deposited on ZnPtriazine(gly)2-modified TiO2.63 This is consistent with a reduction in the amount of grain boundaries (sample where trap states are localized) in the MAPbI3 film. Moreover, the PL intensity of the MAPbI3 film grown in ZnPtriazine(gly)2-coated TiO2 is substantially decreased to 25% of that of the reference perovskite film (grown on TiO2). Since the grain size of the perovskite film deposited on TiO2/ZnPtriazine(gly)2 substrate increases compared to the reference sample, which should increase the PL intensity due to less non-radiative recombination losses, the observed PL quenching of perovskite film deposited on porphyrin-modified TiO2 can only be explained by an increase in charge separation and electron injection efficiency at the metal oxide/perovskite interface. This was further supported by time-resolved photoluminescence (TRPL) measurements taken in similar films; the PL decays, detected at the peak of the PL spectrum are shown in Figure 2f. The TRPL decays were fitted with a bi-exponential decay function (the fitting parameters to be summarized in Table S3 together with the χ2 values) in agreement with the literature.36,64,65 According to Shi at al. the short and long components (τ1 and τ2) are correlated to surface and to bulk properties of the material, respectively.65 The lifetimes and amplitudes found for the perovskite/TiO2 sample are similar to those found by 8 ACS Paragon Plus Environment

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Yang et al. for a similar perovskite on TiO2 surface.36 Upon porphyrin modification of TiO2, a pronounced decrease in the short lifetime component (τ1=0.73 ns with amplitude 92%) compared to that determined for the reference sample (τ1=1.40 ns with amplitude 90%) is evident indicating efficient exciton dissociation and enhanced charge separation and electron transfer towards TiO2 in the sample with the TiO2/ZnPtriazine(gly)2/perovskite interface. Notably, the second long lifetime component (τ2), although of low amplitude (8-10%), was necessary to accurately fit our data. A significant increase from 26 to 47 ns with negligible change in the amplitude probably indicates longer exciton diffusion lengths,65 which could be due to lower trap density at grain boundaries in the modified sample but further investigation is needed. From the above study, it is evident that porphyrin modification of TiO2 brings some beneficial effects such as faster electron transfer towards TiO2 and improved homogeneity/nanomorphology of the perovskite layer. We, therefore, fabricated PSCs using TiO2/ZnPtriazine(gly)2 to compare with the as-deposited TiO2 ETL. In Figure 3a the planar perovskite solar cell configuration is presented. The device utilizes methylammonium lead iodide (CH3NH3PbI3, MAPbI3), as the absorber while also incorporates TiO2 and SpiroMeOTAD as electron and hole transport layers, respectively. ZnPtriazine(gly)2 is applied in the form of an ultra-thin layer on TiO2 to serve as electron transport interfacial layer/surface modifier deposited from a 0.3 mg mL-1 methanolic solution that gave the best device performance among the solutions tested having concentrations 2.0, 1.0, 0.5, 0.3 and 0.1 mg mL-1 (data not shown). Note that, porphyrin coverage had no significant effect on substrate transmittance (Figure S10) which is a highly important issue since the modified metal oxide is placed at the transparent side of the device and, therefore, at the pathway that light follows to reach the perovskite layer. Moreover, the WF of TiO2 before and after porphyrin coverage is nearly aligned to the conduction band (CB) of the perovskite film which implies that 9 ACS Paragon Plus Environment


barrier-free electron extraction should be expected. Figure 3b presents the energy level alignment of the layers sequence applied in the solar cells (before contact) (it shows the WF values for FTO, TiO2 and Ag, the CB and valence band (VB) edges for MAPbI3 and highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital positions for SpiroMeOTAD). Figure 3c presents the J-V characteristic curves (taken in reverse scan under AM 1.5G illumination) of the champion PSCs before and after porphyrin modification. The reference device using as-deposited TiO2 yields a short-circuit current (Jsc) of 21.30 mA cm-2, an opencircuit voltage (Voc) of 1021 mV and a fill factor (FF) of 69% resulting in a PCE of 15.01% (Table 1). An enhanced PCE of 16.87% was obtained when modifying TiO2 layer with ZnPtriazine(gly)2 which represents a 12% enhancement compared to the reference device. The key parameter is the increase in Jsc up to 23.81 mA cm-2 (with Voc of 1012 mV and FF of 70%). The large enhancement in Jsc was further supported by the increase in the incidentphoton-to-current-efficiency (IPCE) of the ZnPtriazine(gly)2-modified cell compared to the reference one, as evidenced by IPCE-action spectrum measurements shown in Figure 3d along with the integrated photocurrent densities, expected under 1 sun illumination. The results, as depicted by the plots of the integrated photocurrent density values, are consistent with the values of the current density (deviation smaller than 1%) obtained by the J-V curves under AM 1.5G irradiation. The photocurrent generated for both devices is mainly located in the visible and near IR region as expected according to the energy band gap of the MAPbI3, while the peak values are below 750nm. Moreover, they present IPCE values which are greater than 85% for the reference and 90% for the modified device respectively. The higher IPCE values of the modified cell can be related to the well-known electron transfer capability of porphyrin molecule which mediates improved injection of photoinduced electrons towards TiO2 leading to enhanced electron collection at the respective contact as also indicated by PL 10 ACS Paragon Plus Environment

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measurements. The formation of a perovskite film composed of sufficiently larger nanocrystallites while also having a more uniform/homogeneous morphology when deposited on ZnPtriazine(gly)2-modified TiO2 also contributes to enhanced photocurrent generation thus improving the photon-to-electron conversion efficiency. Although our champion devices clearly suggest enhanced performance upon porphyrin modification, in order to exclude the experiment accidental errors, the statistical data of devices using as-deposited and ZnPtriazine(gly)2-modified TiO2 were extracted from a batch of 16 individual cells. Figure 4 a-d presents the statistical data for Jsc, Voc, FF and PCE, respectively, along with the standard box plots. As can be seen, the average Jsc of the porphyrin-modified cells is significantly higher than that of the reference device while average Voc and FF values are comparable for both types of cells. As a result, the average PCE of the modified cells is 14.33% corresponding to an enhancement of 14% compared to 12.53% of the devices using as-deposited TiO2. However, the efficiencies even in our champion devices remain below the high values obtained in the state-of-the-art devices as a result the relatively low Voc and FF values.66 Low FF is usually caused by high series resistance and/or low shunt resistance as well as by recombination losses in the absorbing layer.67 Since the latter usually occurs at grain boundaries the small improvement in the FF of the porphyrin modified cell is probably originated from the lower amount of grain boundaries present in this sample. Since the WF of TiO2 (before and after porphyrin modification) is close to the CB of the perovskite layer the origin of the low Voc lies on the defect-rich surface of our TiO2 samples as indicated from the broad visible emission of as-deposited TiO2 (Figure S11).68 We believe that the implementation of our porphyrin-based electron transfer interlayer on defect-free electron transport materials such as SnO2 could allow the achievement of efficiencies higher than those obtained using TiO2 ETLs.



One major problem faced by planar PSCs based on TiO2 ETLs is their hysteretic behavior which is attributed to defects associated with the non-stoichiometry or thermal decomposition. These defects are mainly located at the interfaces and grain boundaries and act as charge traps causing trapping and de-trapping process of the charge traps.69 We verified that our reference devices suffer from severe hysteresis as shown in Figure 5a. Upon porphyrin modification the hysteretic behaviour although it remains significant is, however, aleviated leading to smaller difference in photocurrent between forward and reverse scan directions (Figure 5b). We believe that the increase in the grain size of the perovskite film may result in the pronounced improvement in the hysteretic behaviour of the porphyrinmodified cell compared to the reference as was recently reported in the literature.70 However, since our porphyrin modification approach does not passivate interface traps a large hysteretic behaviour is still present in the modified cells.71-73 Moreover, stabilized solar cell data were obtained by using maximum power point tracking.74 Figure 5c shows the stabilized PCE obtained while holding the solar cell at the maximum point voltage which was found equal to 0.77 V for 120 s. The PCE measured under these conditions corresponds to the steady-state power output of the device. We obtain a stabilized PCE of 14.40% for the porphyrin-modified cell and only of 10.70% for the reference one. All data presented thus far unambiguously indicate that the insertion of a thin porphyrin interlayer between the perovskite film and the TiO2 ETL results in significant improvement of the device efficiency, hysteresis and stabilized power output. However, one major obstacle to broad application of PSCs is their well-known instability under ambient conditions. The temporal stability of intentionally non-encapsulated devices was evaluated through monitoring their J-V characteristic curves as a function of storage time in air. The samples were stored in a silica dried desiccator under dark between measurements and tested in ambient conditions. In Figure 6a–c the evolution of the device operational 12 ACS Paragon Plus Environment

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characteristics for an aging period of 200 hours is presented. These measurements suggest that the efficiency loss in our devices is mainly driven by the photocurrent decline induced by exposure to ambient which is correlated to accumulation of charges at the interfaces, loss of grain-like nanomorphology of the perovskite film and migration of ionic defects in the perovskite phase.75 However, the loss in Jsc and PCE is more pronounced in the reference cell which degrades to 67% of its initial PCE after 200h; on the contrary, the porphyrin-modified cell retains more than 86% of its initial PCE for the same time period while being resting in the dark between measurements. To explain the environmental stability of perovskite films deposited on as-deposited and porphyrin-modified TiO2 we then monitored their absorption spectra immediately after deposition and after being stored in our lab conditions (humidity of 30% and temperature of 20 oC) for two months (Figures 7a and 7c). The insets show the corresponding photographs of fresh and degraded perovskite films grown on both types of TiO2 substrates. From the pronounced reduction in absorption and color bleaching of the reference perovskite film becomes evident that when it is deposited directly on TiO2 undergoes severe degradation after the period of two months. On the contrary, the film deposited on the porphyrin-modified TiO2 presents smaller decrease in the visible absorption indicating that it does not degrade noticeably while also nearly retains its dark color. Furthermore, the evolution of perovskite film nanomorphology after being exposed to ambient conditions for the time period of two months was investigated. Figures 7b and 7d present top-view SEM images of perovskite films grown on as-deposited and porphyrin-modified TiO2, respectively, taken two months after deposition. A substantial material decomposition to small particles with only a small amount of the characteristic perovskite grains is observed for the reference sample. On the other hand, the film deposited on the porphyrin-coated TiO2 still preserves a large amount of the initially formed grains. Moreover, X-ray diffraction (XRD) patterns of fresh and degraded 13 ACS Paragon Plus Environment


samples were recorded to unravel the beneficial effect of porphyrin-modification of TiO2 on the environmental stability of the perovskite film. As shown in Figures 7e and 7f the coverage of TiO2 with ZnPtriazine(gly)2 did not alter the growth direction of MAPbI3 film; identical peaks which are attributed to the tetragonal crystal structure of MAPbI3 are present in both XRD spectra.76 However, the intensity of these peaks is increased while the FWHM of the (110) peak decreases from 0.149 degrees for the reference sample to 0.136 degrees upon perovskite growth on porphyrin-coated TiO2 implying a slight improvement in crystallinity of the latter film (the thicknesses of perovskite films are similar). Notably, traces of PbI2 were found in both types of fresh perovskite films indicating a small degree of nonstoichiometry in the films. This deviation from stoichiometry could be the reason for the large hysteresis effect observed even in the high efficiency devices. The dramatic change in the morphology of the reference upon aging is followed by a severe loss in crystallinity and an increase in the intensity of the PbI2 peak (Fig. 7e). This provides evidence for the wellknown degradation process of the perovskite film driven by the adsorption of environmental water which causes hydrolysis of the perovskite material and produces PbI2 upon the release of gas phase HI and CH3NH2 species.77 On the contrary, the crystallinity loss and the intensity of the PbI2 peak appear quite modest in the porphyrin-modified sample (Fig. 7f). It has been reported that grain boundaries are vulnerable sites for degradation since they cause charge carrier accumulation while also acting as infiltration pathway of water.19,78 The improved morphology of the perovskite film grown on the porphyrin-modified substrate which consists of smaller amount of grain boundaries compared to the reference sample retards its degradation by restricting the carrier accumulation and preventing water adsorption at grain boundaries. The hydrophobic nature of porphyrin layer results in a reduction of the amount of adsorbed water molecules on the surface of TiO2 prior to the


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deposition of perovskite films thus protecting from water-induced degradation the underlying perovskite film. Similar results were obtained using Raman spectra analysis which also permit the identification of PbI2 formed as a degradation product after the films were exposed to ambient air conditions. PbI2 Raman signal presents characteristic bands at 97, 112 and 213 cm-1 (see inset Figure 8a) in accordance to the literature.79,80 As shown in Figure 8a, the integrated PbI2 Raman signal exceeds the noise level after 10 days of air storage and becomes very strong for perovskite films aged for 200 days. On top, the PbI2 signal for the perovskite films grown on porphyrin-modified TiO2 is systematically lower (about twice) than that of the reference films. The intense PbI2 formation of the 200 h aged films was further tested by performing Raman mapping (Figure 8 c-h) across relatively large film areas (Figure S12a presents the actual pictures of the 200 days aged films). The optical, Raman and blended dual images clearly show that the PbI2 Raman signal is correlated with the areas observed yellowish under the optical microscope. The porphyrin-based film presents considerably less overall PbI2 signal (30,000 counts) relative to the reference (25,000-55,000 counts). Furthermore, in the porphyrin-modified film both large areas which are almost intact (I) from degradation products and big isolated PbI2 islands (P) are observed. On the other side, the reference film is almost fully covered by PbI2 which agrees well with the complete degradation of grain-like morphology of this sample (Figure S12b) compared to the porphyrin-modified one which consists of large grains with degraded areas between them (Figure S12c). Micro-PL was used to determine the physicochemical differences between the films at the early stage of exposure in air. Thus the films were examined after 2 hours, 1 day and 10 days of exposure and the evolution of the PL signal above 788 nm is shown in Figure 8b. The reference films show dramatic enhancement of the PL emission level upon air exposure time



correlated to the moisture adsorbed in the films.81 On the contrary, the porphyrin based films present only moderate PL enhancement clearly elucidating the optimized stabilization upon modification. Furthermore, all films present increase in the PL intensity under light soaking which is characteristic property of MAPbI3 exposed in air and is attributed to irradiation induced healing of the materials from charge carriers traps.81,82 Decomposition of the material finally results in non-uniform PL characteristics of the films (as shown in the Figure 8b for the 200 days aged films), which in the intact areas (I) present very strong PL signal and in the areas where PbI2 has been formed (P) present negligible signal.

3. Conclusions Inserting a thin porphyrin layer between the MAPbI3 film and the TiO2 ETL planar enabled the fabrication of planar PSCs with a maximum PCE of 16.87% (average 14.33%) and a stabilized power output of 14.40% compared to 15.01% (average 12.53%) and 10.70%, respectively, of the reference cells. The porphyrin compound was substituted with two glycine moieties bearing carboxylic acid groups for strong anchoring on metal oxide substrate and one triazine withdrawing spacer for accelerating electron transfer towards TiO2. The efficiency enhancement was the result of the large increase in Jsc which originates from the remarkable electron transfer capability of porphyrin molecules. The homogeneous morphology of the perovskite film grown on the porphyrin-modified substrate and its slightly increased crystallinity offered a small increase in the device FF. Importantly, the growth of perovskite films on porphyrin-modified substrates substantially retarded their degradation which was attributed to the water induced decomposition of MAPbI3 to PbI2. As a result, porphyrin-modified cells retained about 86% while reference cells degraded to 67% of their initial PCE after 200h. 16 ACS Paragon Plus Environment

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4. Experimental section Fabrication and characterization of perovskite solar cells. The perovskite solar cells were fabricated by depositing the successive layers upon 20mmx15mm FTO substrates (Aldrich, 7 Ohm/sq). The conductive glasses were patterned with a 2M HCl solution and zinc powder and were thoroughly cleaned and sonicated in 15 min cycles with Triton-X, acetone, 2propanol and UV ozone. TiO2 was spin coated at 2000 r.p.m. for 60s from a mildly acidic solution of titanium(IV) isopropoxide (Aldrich, 97%) in ethanol. The films obtained, were annealed at 500 oC under a 5oC/min temperature ramp and subsequently were transferred into an Ar-filled glove box for the further experimental procedures. Then thin porphyrin layers were deposited on TiO2 via spin coating methanolic solutions with concentrations 2.0, 1.0, 0.5, 0.3 and 0.1 mg mL-1 at 2000 rpm for 40 sec without any post-annealing step. The CH3NH3PbI3 layer was then deposited by spin coating a perovskite solution at 2000 rpm for 45s. The films were left to dry at room temperature for 5 min and were annealed at 100o for 10 min. The perovskite solution was prepared by mixing a 40 wt% methylammonium iodide (Dyesol) precursor in anhydrous N,N-dimethylformamide, along with Lead acetate trihydrate (PbAc2.3H2O, 99.999% trace metals basis, Aldrich) in a 3:1molar ratio. A small amount of hypophosphorous acid (50% w/w, aquatic solution, Alfa Aesar) was added so as the final molar ratio of HPA:PbAc2 to be 1:4. Finally, a 7 wt% Spiro-MeOTAD (Solaronix) as hole transport layer was deposited from a chlorobenzene solution containing additives of lithium bis(trifluoromethanesulfonyl)imide lithium salt (≥99%, Aldrich) in acetonitrile and 4-tertbutylpyridine (96%, Aldrich) at 3000 r.p.m for 30 s. Finally, the devices were transferred outside the glove-box and 100nm silver electrodes were thermally evaporated under vacuum of 10 -6 Torr, at a rate of ~1Å s-1.



Current density-voltage (J-V) characteristic plots were obtained by illuminating the PSCs under a Solar Light Co. 300W Air Mass Solar Simulator Model 16S-300 (1sun, 1000 W/m2). The curves were recorded on an Autolab PG-STAT-30 potentiostat with a scan rate of 300mVs-1. The cells were illuminated from the anode (active area of 0.12 cm2) while the measurements were carried out using Ossila’s Push-Fit Test Board for Photovoltaic Substrates without an aperture mask. Stabilized maximum power point (MPP) tracking characterization of solar cells with and without ZnPtriazine(gly)2 was carried out in 0.77V bias in 1 sun illumination. Finally, the IPCE measurements were carried out by a custommade apparatus consisting of an Oriel monochromator and an Oriel Xe lamp working in combination with AM 1.5G, AM 0 and 400 nm (ultraviolet-UV) cut off optical filters. The curves were recorded on the Autolab PG-STAT-30 potentiostat. Both lamps were calibrated using an Optopolymer Si reference cell. Measurements and Instrumentation. XPS and UPS spectra were recorded by Leybold EA11 electron analyzer operating in constant energy mode at pass energy of 100 eV and at a constant retard ratio of 4 eV. The X-ray source was an unmonochromatized Mg Kα line at 1253.6 eV (12 kV with 20 mA anode current) while the source for UPS was He I line (21.22 eV). Steady-state PL spectra were recorded using a blue laser diode module emitting at 450 nm as the excitation source and a Si photodiode as the detector while they were analyzed by using an Oriel 77200 monochromator. The PL signal was corrected to the response of the system. The TRPL decays were detected by means of a Time Correlated Single Photon Counting (TCSPC) technique employing a pulse diode laser at 400 nm as excitation source (Picoquant). The Instrument's Response Function was 100 ps. Detection of the perovskite PL decays was realized at 780 nm. UV-Vis absorption and transmittance measurements were taken using a Perkin Elmer Lambda 40 UV/Vis spectrometer. XRD patterns were obtained with a Siemens D500 diffractometer with Cu-Ka radiation while AFM measurements were 18 ACS Paragon Plus Environment

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performed with an NT-MDT atomic force microscope operated in tapping mode. The sample morphologies were investigated using a FESEM (JEOL 7401f). Micro-Raman measurements were carried out by laser excitation at 514.5 nm with 0.02 mW µm-2 by focusing on 1 µm2 with a x50 magnification lens. Results presented are averaged over 10 different spots, in order to avoid statistical errors. The Raman mapping was done on 30x30 µm2 areas with 2.5 µm steps and the power density was increased to 0.2 mW µm2, in order to enable reasonable acquisition times. All Raman measurements were performed in backscattering geometry on an InVia Renishaw spectrometer. Micro-Photoluminescence measurements were carried in the same system by excitation at 785 nm. A x100 lens was used to focus the laser light on spots of ≈1 µm2 and the power density was adjusted to 5x10-5 mW µm-2. These excitation parameters constitute minimum light stress on the sample combined with minimization of the PL background.63 Such conditions are ideal for getting strong PL signals in short time as well as recording PL intensity vs. time, even though only the PL tail, above 788 nm (and not the PL peak at ≈780 nm) can be monitored. Mean data taken from 6 different points are presented.

Acknowledgments This work was supported by European Union’s Horizon 2020 Marie Curie Innovative Training Network 764787 “MAESTRO” project. ΙΚΥ Scholarship Programs, Strengthening Post-Doctoral Research Human Resources Development Program, Education and Lifelong Learning,co-financed by the European Social Fund – ESF and the Greek government is also acknowledged.



Supporting Information Additional Information (Figure S1-S12) and Tables (S1,S2) includes the synthesis and gasphase geometry optimization of porphyrin molecule, the absorption and emission spectra of porphyrin in solution and in film, transmittance spectra of TiO2, reflectance and IQE spectra of PSCs, AFM and contact angle measurements of TiO2, photographs of degraded perovskite films.


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References 1. Liu, M.; Johnston, M. B.; Snaith, H. J. Efficient Planar Heterojunction Perovskite Solar Cells by Vapour Deposition. Nature 2013, 501, 395-398. 2. Lee, J.-W.; Seol, D.-J.; Cho, A.-N.; Park, N.-G. High-Efficiency Perovskite Solar Cells Based on the Black Polymorph of HC(NH2)2 PbI3. Adv. Mater. 2014, 26, 4991. 3. Zhou, H.; Chen, Q.; Li, G.; Luo, S.; Song, T.-B.; Duan, H.-S.; Hong, Z.; You, J.; Liu, Y.; Yang, Y. Photovoltaics. Interface Engineering of Highly Efficient Perovskite Solar Cells. Science 2014, 345, 542. 4. Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Solar Cells. High-Performance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange. Science 2015, 348, 1234. 5.

Fabini, D. H.; Stoumpos, C. C.; Laurita, G.; Kaltzoglou, A.; Kontos, A. G.; Falaras, P.; Kanatzidis, M. G.; Seshadri. R. Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide. Angewandte Chemie International Edition 2016, 55, 15392–15396.

6. Lee, M. M.; Teuscher, J.; Miyasaka, J. T.; Murakami, T. N.; Snaith, H. J. Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites. Science, 2012, 338, 643. 7. Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Gratzel, M.; Park, N.-G. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Scientific Reports 2012, 2, 591. 8. Ball, J. M.; Lee, M. M.; Hey, A.; Snaith, H. J. Low-Temperature Processed MesoSuperstructured to Thin-Film Perovskite Solar Cells. Energy Environ. Sci. 2013, 6, 1739.



9. Kuang, C.; Tang, G.; Jiu, T.; Yang, H.; Liu, H.; Li, B.; Luo, W.; Li, X.; Zhang, W.; Lu, F.; Fang, J.; Li, Y. Highly Efficient Electron Transport Obtained by Doping PCBM with Graphdiyne in Planar-Heterojunction Perovskite Solar Cells. Nano Lett. 2015, 15, 2756. 10. Azimi, H.; Ameri, T.; Zhang, H.; Hou, Y.; Quiroz, C. O. R.; Min, J.; Hu, M.; Zhang, Z.G.; Przybilla, T.; Matt, G. J.; Spiecker, E.; Li, Y.; Brabec, C. J. A Universal Interface Layer Based on an Amine-Functionalized Fullerene Derivative with Dual Functionality for Efficient Solution Processed Organic and Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1401692. 11. Hou, Y.; Du, X.; Scheiner, S.; McMeekin, D. P.; Wang, Z.; Li, N.; Killian, M. S.; Chen, H.; Richter, M.; Levchuk, I.; Schrenker, N.; Spiecker, E.; Stubhan, T.; Luechinger, N. A.; Hirsch, A.; Schmuki, P.; Steinrück, H.-P.; Fink, R. H.; Halik, M.; Snaith, H. J.; Brabec, C. J. A Generic Interface to Reduce the Efficiency-Stability-Cost Gap of Perovskite Solar Cells. Science 2017, 358, 1192–1197. 12. Christians, J. A.; Schulz, P.; Tinkham, J. S.; Schloemer, T. H.; Harvey, S. P.; Tremolet de Villers, B. J.; Sellinger, A.; Berry, J. J.; Luther, J. M. Tailored Interfaces of Unencapsulated Perovskite Solar Cells for >1,000 Hour Operational Stability. Nature Energy 2018, 3, 68–74. 13. Jiang, L.; Zheng, J.; Chen, W.; Huang, Y.; Hu, L.; Hayat, T.; Alsaedi, A.; Zhang, C.; Dai., S. High-Performance Perovskite Solar Cells with a Weak Covalent TiO2:Eu3+ Mesoporous Structure. ACS Appl. Energy Mater. 2018, 1 (1), 93–102. 14. Sung, S. D.; Ojha, D. P.; You, J. S.; Lee, J.; Kim J.; Lee, W. I. 50 nm Sized Spherical TiO2 Nanocrystals for Highly Efficient Mesoscopic Perovskite Solar Cells. Nanoscale 2015, 7, 8898-8906. 15. Lee, J. W.; Lee, T. Y.; Yoo, P. J.; Grätzel, M.; Mhaisalkar, S.; Park, N. G. Rutile TiO2Based Perovskite Solar Cells. Journal of Materials Chemistry A 2014, 2, 9251-9259.


Page 22 of 42

Page 23 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


16. Huang,Y.; Zhu, J.; Ding, Y.; Chen, S.; Zhang, C.; Dai,S. TiO2 Sub-Macrosphere Film as Scaffold Layer for Efficient Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2016, 8, 8162–8167. 17. Giordano, F.; Abate, A.; Baena, J. P. C.; Saliba, M.; Matsui, T.; Im S. H.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Hagfeldt, A.; Graetzel, M. Enhanced Electronic Properties in Mesoporous TiO2 via Lithium Doping for High-Efficiency Perovskite Solar Cells. Nature Communications 2016, 7, 10379. 18. Zhu, Z.; Ma, J.; Wang, Z.; Mu, C.; Fan, Z.; Du, L.; Bai, Y.; Fan, L.; Yan, H.; Phillips, D. L.; Yang, S. Efficiency Enhancement of Perovskite Solar Cells Through Fast Electron Extraction: The Role of Graphene Quantum Dots. J. Am. Chem. Soc. 2014, 136, 3760– 3763. 19. Xiao, M.; Huang, F.; Huang, W.; Dkhissi, Y.; Zhu, Y.; Etheridge, J.; Weale, A. G.; Bach, U.; Cheng, Y. B.; Spiccia. L.; A Fast Deposition-Crystallization Procedure for Highly Efficient Lead Iodide Perovskite Thin-Film Solar Cells. Angew. Chem. Int. Ed. 2014, 53, 9898–9990. 20. Zuo, L.; Dong, S.; Marco, N. D.; Hsieh, Y.-T.; Bae, S.-H.; Sun, P.; Yang, Y. Morphology Evolution of High Efficiency Perovskite Solar Cells via Vapor Induced Intermediate Phases. J. Am. Chem. Soc. 2016, 138, 15710–15716. 21. Salim, T.; Sun, S.; Abe, Y.; Krishna, A.; Grimsdale, A. C.; Lam, Y. M. Perovskite-based Solar Cells: Impact of Morphology and Device Architecture on Device Performance. J. Mater. Chem. A 2015, 3, 8943. 22. Leijtens, T.; Eperon, G. E.; Noel, L. K.; Habisreutinger, S. N.; Petrozza, A.; Snaith, H. J. Stability of Metal Halide Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1500963.



23. Yang, J.; Siempelkamp, B. D.; Liu, D.; Kelly, T. L. Investigation of CH3NH3PbI3 Degradation Rates and Mechanisms in Controlled Humidity Environments Using in Situ Techniques. ACS Nano 2015, 9(2), 1955–1963. 24. Christians, J. A.; Herrera, M. P. A.; Kamat, P. V. Transformation of the Excited State and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite Upon Controlled Exposure to Humidified Air. J. Am. Chem. Soc. 2015, 137, 1530–1538. 25. Habisreutinger, S. N.; Leijetens, T.; Eperon, G. E.; Stranks S. M.; Nicholas R. J.; Snaith, H. J. Carbon Nanotube/Polymer Composites as a Highly Stable Hole Collection Layer in Perovskite Solar Cells. Nano Lett. 2014, 14, 5561–5568. 26. Chen, W.; Wu, W.; Yue, Y.; Liu, J.; Zhang, W.; Yang, X.; Chen, H.; Bi, E.; Ashraful, I.; Grätzel, M.; Han, L. Efficient and Stable Large-Area Perovskite Solar Cells with Inorganic Charge Extraction Layers. Science 2015, 350, 944–948. 27. Wojciechowski, K.; Leijtens, T.; Siprova, S.; Schlueter, C.; Hörantner, M. T.; Wang, J. T.-W.; Li, C.-Z.; Jen, A. K.-Y.; Lee, T.-L.; Snaith, H. J. C60 as an Efficient n-type Compact Layer in Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 2399–2405. 28. You, J.; Meng, L.; Song, T.-B.; Guo, T.-F.; Yang, Y. (M.).; Chang, W.-H.; Hong, Z.; Chen, H.; Zhou, H.; Chen, Q.; Liu, Y.; Marco, N. D.; Yang Y. Improved Air Stability of Perovskite Solar Cells via Solution-Processed Metal Oxide Transport Layers. Nat. Nanotechnol. 2016, 11, 75–81. 29. Leijtens, T.; Eperon, G. E.; Pathak, S.; Abate, A.; Lee, M. M.; Snaith, H. J. Overcoming Ultraviolet Light Instability of Sensitized TiO₂ with Meso-Superstructured Organometal Tri-Halide Perovskite Solar Cells. Nat Commun. 2013, 4, 2885. 30. Bella, F.; Griffini, G.; Correa-Baena, J. P.; Saracco, G.; Grätzel, M.; Hagfeldt, A.; Turri, S.; Gerbaldi, C. Improving Efficiency and Stability of Perovskite Solar Cells with Photocurable Fluoropolymers. Science 2016, 354, 203–206.


Page 24 of 42

Page 25 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


31. Zuo, L.; Gu,Z .; Ye, T.; Fu, W.; Wu, G.; Li, H.; Chen, H. Enhanced Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells Through Interfacial Engineering Using Self‐Assembling Monolayer. J. Am. Chem. Soc. 2015, 137, 2674–2679. 32. Wojciechowski, K.; Stranks, S. D.; Abate, A.; Sadoughi, G.; Sadhanala, A.; Kopidakis, N.; Rumbles, G.; Li, C.-Z.; Friend, R. H.; Jen, A. K. Y.; Snaith, H. J. Heterojunction Modification for Highly Efficient Organic-Inorganic Perovskite Solar Cells. ACS Nano 2014, 8, 12701–12709. 33. Li, Y.; Zhao, Y.; Chen, Q.; Yang, Y. (M.); Liu, Y.; Hong, Z.; Liu, Z.; Hsieh, Y.-T.; Meng, L.; Li, Y.; Yang, Y. Multifunctional Fullerene Derivative for Interface Engineering in Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137, 15540–15547. 34. Li, W.; Zhang, W.; Reenen, S. V.; Sutton, R. J.; Fan, J.; Haghighirad, A. A.; Johnston, M. B.; Wang, L; Snaith, H. J. Enhanced UV-Light Stability of Planar Heterojunction Perovskite Solar Cells with Caesium Bromide Interface Modification. Energy Environ. Sci. 2016, 9, 490–498. 35. Cao, J.; Yin, J.; Yuan, S.; Zhao, Y.; Li, J.; Zheng, N. Thiols as Interfacial Modifiers to Enhance the Performance and Stability of Perovskite Solar Cells. Nanoscale 2015, 7, 9443–9447. 36. Yang, D.; Zhou, X.; Yang, R.; Yang, Z.; Yu, W.; Wang, X.; Li, C.; Liu, S. (F.); Chang, R. P. H. Surface Optimization to Eliminate Hysteresis for Record Efficiency Planar Perovskite Solar Cells. Energy Environ. Sci. 2016, 9, 3071–3078. 37. Peng, J.; Wu,a Y.; Ye, W.; Jacobs, D. A.; Shen, H.; Fu, X.; Wan, Y.; Duong, T.; Wu, N.; Barugkin, C.; Nguyen, H. T.; Zhong, D.; Li, J.; Lu, T.; Liu, Y.; Lockrey, M. N.; Weber, K. J.; Catchpolea, K. R.; White, T. P. Interface Passivation Using Ultrathin Polymer–Fullerene Films for High-Efficiency Perovskite Solar Cells with Negligible Hysteresis. Energy Environ. Sci. 2017, 10, 1792–1800.



38. Liu, D.; Li, S.; Zhang, P.; Wang, Y.; Zhang, R.; Sarvari, H.; Wang, F.; Wu, J.; Wang, Z.; Chen, Z. D. Efficient Planar Heterojunction Perovskite Solar Cells with Li-Doped Compact TiO2 layer. Nano Energy 2017, 31, 462–468. 39. Tan, H.; Jain, A.; Voznyy, O.; Lan, X.; García de Arquer, F. P.; Fan, J. Z.; QuinteroBermudez, R.; Yuan, M.; Zhang, B.; Zhao, Y.; Fan, F.; Li, P.; Quan, L. N.; Zhao, Y.; Lu, Z. H.; Yang, Z.; Hoogland, S.; Sargent, E. H. Efficient and Stable Solution-Processed Planar Perovskite Solar Cells via Contact Passivation. Science 2017, 355, 722–726. 40. Han, G. S.; Chung, H. S.; Kim, B. J.; Kim, D. H.; Lee, J. W.; Swain, B. S.; Mahmood, K.; Yoo, J. S.; Park, N.-G.; Lee, J. H.; Jung, H. S. Retarding Charge Recombination in Perovskite Solar Cells Using Ultrathin MgO-Coated TiO2 Nanoparticulate films. J. Mater. Chem. A 2015, 3, 9160–9164. 41. Baena, J. P. C.; Steier, L.; Tress, W.; Saliba, M.; Neutzner, S.; Matsui, T.; Giordano, F.; Jacobsson, T. J.; Kandada, A. R. S.; Zakeeruddin, S. M.; Petrozza, A.; Abate, A.; Nazeeruddin, M. K.; Grätzel, M.; Hagfeldt. A. Highly Efficient Planar Perovskite Solar Cells Through Band Alignment Engineering. Energy Environ. Sci. 2015, 8, 2928–2934. 42. Hu, T.; Becker, T.; Pourdavoud, N.; Zhao, J.; Brinkmann, K. O.; Heiderhoff, R.; Gahlmann, T.; Huang, Z.; Olthof, S.; Meerholz, K.; Többens, D.; Cheng, B.; Chen, Y.; Riedl. T. Indium‐Free Perovskite Solar Cells Enabled by Impermeable Tin‐Oxide Electron Extraction Layers. Adv. Mater. 2017, 19, 1606656. 43. Jung, K.-H.; Seo, J.-Y.; Lee, S.; Shin, H.; Park, N.-G. Solution-Processed SnO2 Thin Film for a Hysteresis-Free Planar Perovskite Solar Cell with a Power Conversion Efficiency of 19.2%. Mater. Chem. A 2017, 5, 24790–24803 44. Mathew, S.; Yella, A.; Gao, P. ; Humphry-Baker, R.; Curchod, B. F.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M.; Grätzel, M. Dye-Sensitized Solar Cells 26 ACS Paragon Plus Environment

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with 13% Efficiency Achieved through the Molecular Engineering of Porphyrin Sensitizers. Nat. Chem. 2014, 6, 242–247. 45. Li, L.-L.; Diau, E.W.-D. Porphyrin-Sensitized Solar Cells. Chem. Soc. Rev. 2013, 42, 291–304. 46. Kesters, J.; Verstappen, P.; Kelchtermans, M.; Lutsen, L.; Vanderzande, D.; Maes, W. Porphyrin-Based Bulk Heterojunction Organic Photovoltaics: The Rise of the Colors of Life. Adv. Energy Mater. 2015, 5, 1500218. 47. Li, B.; Zheng, C.; Liu, H.; Zhu, J.; Zhang, H.; Gao, D.; Huang, W. Large Planar πConjugated Porphyrin for Interfacial Engineering in p-i-n Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2016, 8, 27438–27443. 48. Chen, S.; Liu, P.; Hua, Y.; Li, Y.; Kloo, L.; Wang, X.; Ong, B. S.; Wong, W.-K.; Zhu, X. Study of Arylamine-Substituted Porphyrins as Hole-Transporting Materials in HighPerformance Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 13231–13239. 49. Chou, H.-H.; Chiang, Y.-H.; Li, M.-H.; Shen, P.-S.; Wei, H.-J.; Mai, C.-L.; Chen, P.; Yeh, C.-Y. Zinc Porphyrin–Ethynylaniline Conjugates as Novel Hole-Transporting Materials for Perovskite Solar Cells with Power Conversion Efficiency of 16.6%. ACS Energy Lett. 2016, 1, 956–962. 50. Vasilopoulou, M.; Georgiadou, D. G.; Douvas, A. M.; Soultati, A.; Constantoudis, V.; Davazoglou, D.; Gardelis, S.; Palilis, L. C.; Fakis, M.; Kennou, S.; Lazarides, T.; Coutsolelos, A. G.; Argitis, P. Porphyrin Oriented Self-Assembled Nanostructures for Efficient Exciton Dissociation in High-Performing Organic Photovoltaics. J. Mater. Chem. A 2014, 2, 182–192. 51. Zhang, L.; Liu, C.; Lai, T.; Huang, H.; Peng, X. Huang, F.; Cao, Y. A Water/AlcoholSoluble Conjugated Porphyrin Small Molecule as a Cathode Interfacial Layer for Efficient Organic Photovoltaics. J. Mater. Chem. A 2016, 4, 15156–15161. 27 ACS Paragon Plus Environment


52. Zhang L.; Cole J. M. Anchoring Groups for Dye-Sensitized Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 3427–3455. 53. Jordan, K. D.; Burrow, P. D. Studies of the Temporary Anion States of Unsaturated Hydrocarbons by Electron Transmission Spectroscopy. Acc. Chem. Res. 1978, 11, 341– 348. 54. Sharma, G. D.; Angaridis, P. A.; Pipou, S.; Zervaki, G. E.; Nikolaou, V.; Misra, R.; Coutsolelos, A. G. Efficient Co-Sensitization of Dye-Sensitized Solar Cells by Novel Porphyrin/Triazine Dye and Tertiary Aryl-Amine Organic Dye. Org. Electron. 2015, 25, 295–307. 55. Qu, Q.; Geng, H.; Peng, R.; Cui, Q.; Gu, X.; Li, F.;Wang, M. Chemically Binding Carboxylic Acids onto TiO2 Nanoparticles with Adjustable Coverage by Solvothermal Strategy. Langmuir 2010, 26 (12), 9539–9546. 56. Nara, M.; Torii, H.; Tasumi, M. Correlation between the Vibrational Frequencies of the Carboxylate Group and the Types of Its Coordination to a Metal Ion: An ab Initio Molecular Orbital Study. J. Phys. Chem. 1996, 100, 19812–19817. 57. Tunesi, S.; Anderson, M. A. Surface Effects in Photochemistry: an in Situ Cylindrical Internal Reflection-Fourier Transform Infrared Investigation of the Effect of Ring Substituents on Chemisorption onto Titania Ceramic Membranes. Langmuir 1992, 8, 487–495. 58. Flechtner, K.; Kretschmann, A.; Bradshaw, L.R.; Walz, M.; Steinrück, H.-P.; Gottfried, J. M. Surface-Confined Two-Step Synthesis of the Complex (Ammine) (mesotetraphenylporphyrinato)-zinc(II) on Ag(111). J. Phys. Chem. C 2007, 111, 5821–5824. 59. Killian, M. S.; Gnichwitz, J.-F.; Hirsch, A.; Schmuki, P.; Kunze, J. ToF-SIMS and XPS Studies of the Adsorption Characteristics of a Zn-Porphyrin on TiO2. Langmuir 2010, 26, 3531–3538.


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60. Vasilopoulou, M.; Douvas, A. M.; Georgiadou, D. G.; Constantoudis, V.; Davazoglou, D.; Kennou, S.; Palilis, L. C.; Daphnomili, D.; Coutsolelos, A. G.; Argitis, P. Large Work Function Shift of Organic Semiconductors Inducing Enhanced Interfacial Electron Transfer in Organic Optoelectronics Enabled by Porphyrin Aggregated Nanostructures. Nano Res. 2014, 7, 679–693. 61. Abate, S. Y.; Wu, W.-T.; Pola, S.; Tao, Y.-T. Compact TiO2 Films with Sandwiched Ag Nanoparticles as Electron-Collecting Layer in Planar Type Perovskite Solar Cells: Improvement in Efficiency and Stability. RSC Adv. 2018, 8, 7847-7854. 62. Fang, H.-H.; Wang, F.; Adjokatse, S.; Zhao, N.; Even, J.; Loi, M. A. Photoexcitation Dynamics in Solution-Processed Formamidinium Lead Iodide Perovskite Thin Films for Solar Cell Applications. Light: Science & Application 2016, 5, e16056. 63. Gomez, A.; Sanchez, S.; Campoy-Quiles, M.; Abate, A. Topological Distribution of Reversible and Non-Reversible Degradation in Perovskite Solar Cells. Nano Energy 2018, 45, 94–100. 64. Zhang, F.; Wang, Z.; Zhu, H.; Pellet, N.; Luo, J.; Yi, C.; Liu, X.; Liu, H.; Wang, S.; Li, X.; Xiao, Y.; Zakeeruddin, S. M.; Bi, D.; Grätzel, M. Over 20% PCE Perovskite Solar Cells with Superior Stability Achieved by Novel and Low-Cost Hole-Transporting materials. Nano Energy 2017, 41, 469–475. 65. Shi, D.; Adinolfi, V.; Comin, R.; Yuan, M.; Alarousu, E.; Buin, A.; Chen, Y.; Hoogland, S.; Rothenberger, A.; Katsiev, K.; Losovyj, Y.; Zhang, X.; Dowben, P.A.; Mohammed, O.F.; Sargent, E.H.; Bakr, O.M. Low Trap-State Density and Long Carrier Diffusion in Organolead Trihalide Perovskite Single Crystals. Science 2015, 347, 519–522. 66. Zhao, X.; Tao, l.; Li, h.; Huang, W.; Sun, P.; Liu, J.; Liu, S.; Sun, Q.; Cui, Z.; Sun, L.; Shen, Y.; Yang, Y.; Wang, M. Efficient Planar Perovskite Solar Cells with Improved Fill Factor via Interface Engineering with Graphene. Nano Lett. 2018, 18 (4), 2442–2449. 29 ACS Paragon Plus Environment


67. Fakharuddin, A.; Schmidt‐Mende, L.; Garcia‐Belmonte, G.; Jose, R.; Mora‐Sero, I. Interfaces in perovskite solar cells. Adv. Energy Mater. 2017, 7, 1700623. 68. Vasilopoulou, M.; Georgiadou, D. G.; Soultati, A.; Boukos, N.; Gardelis, S.; Palilis, L. C.; Fakis, M.; Skoulatakis, G.; Kennou, S.; Botzakaki, M.; Georga, S.; Krontiras, C. A.; Auras, F.; Fattakhova-Rohlfing, D.; Bein, T.; Papadopoulos, T. A.; Davazoglou, D.; Argitis, P. Atomic-Layer-Deposited Aluminum and Zirconium Oxides for Surface Passivation of TiO2 in High-Efficiency Organic Photovoltaics. Adv. Energy Mater. 2014, 4, 1400214. 69. Wong, K. K.; Fakharuddin, A.; Ehrenreich, P.; Deckert, T.; Abdi-Jalebi, M.; Friend, R. H.; Schmidt-Mende. L. Interface Dependent Radiative and Non-Radiative Recombination in Perovskite Solar Cells. J. Phys. Chem. C 2018, DOI: 10.1021/acs.jpcc.8b00998. 70. Hui-Seon Kim and Nam-Gyu Park. Parameters Affecting I−V Hysteresis of CH3NH3PbI3 Perovskite Solar Cells: Effects of Perovskite Crystal Size and Mesoporous TiO2 Layer. J. Phys. Chem. Lett. 2014, 5 (17), 2927–2934. 71. Yang, C.; Wang, J.; Bao, X.; Gao, J.; Liu, Z.; Yang. R. Grain-Boundary Effect and Post Treatment of Active Layer for Efficient Inverted Planar Perovskite Solar Cells. Electrochimica Acta 2018, 281, 9–16. 72. Bisquert, J.; Bertoluzzi, L.; Mora-Sero, I.; Garcia-Belmonte, G. Theory of Impedance and Capacitance Spectroscopy of Solar Cells with Dielectric Relaxation, Drift-Diffusion Transport, and Recombination. J. Phys. Chem. C 2014, 118, 18983–18991. 73. Pockett, A.; Eperon, G. E.; Peltola, T.; Snaith, H. J.; Walker, A.; Peter, L. M.; Cameron, P. J. Characterization of Planar Lead Halide Perovskite Solar Cells by Impedance Spectroscopy, Open-Circuit Photovoltage Decay, and Intensity-Modulated Photovoltage/Photocurrent Spectroscopy. J. Phys. Chem. C 2015, 119, 3456–3465.


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Page 31 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


74. Christians, J. A.; Manser, J. S.; Kamat, P. V. Best Practices in Perovskite Solar Cell Efficiency Measurements. Avoiding the Error of Making Bad Cells Look Good. J. Phys. Chem. Lett. 2015, 6 (5), 852–857. 75. Calado, P.; Telford, A. M.; Bryant, D.; Li X.; Nelson, J.; O’Regan B. C.; Barnes P. R.F. Evidence for Ion Migration in Hybrid Perovskite Solar Cells with Minimal Hysteresis. Nat. Comm. 2016, 7, 13831. 76. Yang, G.; Wang, C.; Lei, H.; Zheng, X.; Qin, P.; Xiong, L.; Zhao, X.; Yan, Y.; Fang, G. Interface Engineering in Planar Perovskite Solar Cells: Energy Level Alignment, Perovskite Morphology Control and High Performance Achievement. J. Mater. Chem. A 2017, 5, 1658–1666. 77. Frost, J. M.; Butler, K. T.; Brivio F.; Hendon C. H.; van Schilfgaarde M.; Walsh, A. Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells. Nano Lett. 2014, 14, 2584–2590. 78. Ahn, N.; Kwak, K.; Jang, M.; S.; Yoon, H.; Lee, B. Y.; Lee, J.-K.; Pikhitsa P. V.; Byun, Junseop.; Choi, M. Trapped Charge-Driven Degradation of Perovskite Solar Cells. Nat. Comm. 2016, 7, 13422. 79. Antoniadou, M.; Siranidu, E.; Vaenas, N.; Kontos, A. G.; Stathatos, E.; Falaras, P. Photovoltaic Performance and Stability of CH3NH3PbI3−xClx Perovskites. Journal of Surfaces and Interfaces of Materials 2014, 2, 1–5. 80. Barbé, J.; Kumar, V.; Newman, M. J.; Lee, H. K. H.; Jain, S. M.; Chen, H.; Charbonneau, C.; Rodenburg, C.; Tsoi, W. C. Dark Electrical Bias Effect on Moisture-Induced Degradation in Inverted Lead Halide Perovskite Solar Cells Measured by Advanced Chemical Probes. Sustainable Energy Fuels 2018, 2, 905–914. 81. Brenes, R.; Guo, D.; Osherov, A.; Noel, N. K.; Eames, C.; Hutter, E. M.; Pathak, S. K.; Niroui, F.; Friend, R. H.; Islam, M. S.; Snaith, H. J.; Bulović, V.; Savenije, T. J.; Stranks,



S. D. Metal Halide Perovskite Polycrystalline Films Exhibiting Properties of Single Crystals. Joule 2017, 1, 155–167. 82. Fu, X.; Jacobs, D. A.; Beck, F. J., Duong, T.; Shen, H.; Catchpole, K. R.; White, T. P. Photoluminescence Study of Time- and Spatial Dependent Light Induced Trap DeActivation in CH3NH3PbI3 Perovskite Films. Phys. Chem. Chem. Phys. 2016, 18, 22557– 22564.


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Tables Table 1 Performance characteristics of the champion cells using as-deposited and ZnPtriazine(gly)2-modified TiO2 ETLs in reverse scan (scan rate: 0.3 V s-1, mask aperture: 0.12 cm-2). ETL Jsc FF PCE Voc (mA cm-2) (mV) (%)

TiO2

21.30

1021

0.69

15.01

TiO2/ZnPtriazine(gly)2

23.81

1012

0.70

16.87



Figures 1.04

TiO2 TiO2/ZnPtriazine(gly)2

1.02

Transmittance (%)

1.00 0.98 0.96 1500 0.94

1588

0.92 2000

1800

1600

1410

1400

1200 -1

1000

Wavenumber (cm )

(a)

(b) UPS HeI

TiO2 TiO2/ZnPtriazine(gly)2

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3.3 eV W F= 4.0 eV

20

19

18

17

1.1 eV

16 20 18 16 14 12 10

8

6

4

2

0

10

8

6

4

2

0

Binding energy (eV)

(c) Figure 1 (a) FTIR transmittance spectra of as-deposited and ZnPtriazine(gly)2-modified TiO2 layers. (b) (Up) Possible binding modes of -COOH group on TiO2: (left) monodentate (esterlike linkage), (middle) bidentate chelating and (right) bidentate bridging. (Down) The chemical structure of ZnPtriazine(gly)2 and its exact binding mode on TiO2. (c) UPS spectra of as-deposited and of ZnPtriazine(gly)2-modified TiO2.


Grain area (μm2) (b)

Number of grains

(a)

Grain area (μm2) (c)

(d) 1

TiO2

TiO2

12



Norm.Intensity

14

PL intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Number of grains

Page 35 of 42

10 8 6 4

exc. 400 nm det. 780 nm

0.1

2 0 720

740

760

780

800

820

840

Wavelength (nm)

0

2

4

6

8

10

12

14

16

18

20

Time (ns)

(e)

(f)

Figure 2 (a) SEM image (top view) of the surface of the perovskite film deposited on TiO2 and (b) histogram of the grain areas of the same perovskite film. (c) SEM image of the perovskite film deposited on ZnPtriazine(gly)2-modified TiO2 and (d) histogram of the grain areas of the same perovskite film. (e) Steady-state PL spectra and (f) transient PL decay characteristics of MAPbI3 films grown on as-deposited and ZnPtriazine(gly)2-modified TiO2 layers.



22

20

20

80

18

70

15

10

16

60

14

50

12

40

10 8

30

6

5

0 0.0

TiO2

20


10 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

4

TiO2

2

TiO2/ZnPtriazine(gly)2 400

450

500

550

600

650

700

-2

24

90

IPCE (%)

-2

100

sc-integrated

25

(mA cm )

(b)

J

(a)

Current density (mA cm )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 42

750

0 800

Wavelength (nm)

Voltage (V)

(c)

(d)

Figure 3 Schematics that show (a) the device architecture and (b) the energy diagram of the perovskite solar cells with the structure FTO/TiO2/ZnPtriazine(gly)2/MAPbI3/SpiroMeOTAD/Ag. (c) J-V characteristics under AM 1.5G illumination of the best performing perovskite solar cells and (d) IPCE spectra and integrated Jsc of the same cells.


1.05

24

1.00

22

0.95

20

0.90

Voc (V)

-2

26

18

0.85

16

0.80

14

0.75

12

0.70

10

TiO2

0.65


TiO2

(a)


(b)

0.80

18

0.75 16

PCE (%)

0.70 0.65

FF

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Jsc (mA cm )

Page 37 of 42

0.60 0.55

14 12 10

0.50 8

0.45 0.40 TiO2

6


TiO2

(c)


(d)

Figure 4 Device performance statistics (16 devices for each condition) for perovskite solar cells with different TiO2 ETLs. (a) Jsc, (b) Voc, (c) FF and (d) PCE. Device parameters are obtained from reverse J−V scans.



-2

Current density (mAcm )

25

20

15

10

5

TiO2 0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.7

0.8

0.9

1.0

Voltage (V)

(a)

-2

Current density (mA cm )

25

20

15

10

5

TiO2/ZnPtriazine(gly)2 0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

Voltage (V)

(b) 20 18 16

14.40%

14

PCE (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 42

12

10.70%

10 8 6 4

TiO2

2


0 0

10 20 30 40 50 60 70 80 90 100 110 120

Time (s)

(c) Figure 5 J-V hysteresis of MAPbI3-based perovskite solar cells based on (a) TiO2 and (b) TiO2/ZnPtriazine(gly)2 ETLs. (c) Stabilized PCE of devices employing as-deposited and porphyrin-modified TiO2 ETLs. 38 ACS Paragon Plus Environment

Page 39 of 42

1100

25

1000

15

Voc (mV)

-2

Jsc (mA cm )

20

10

5

900

800

700

TiO2

TiO2

TiO2/ZnPtriazine(gly)2 0 20


40

60

80

20

100 120 140 160 180 200

40

60

Aging time (h)

80

100 120 140 160 180 200

Aging time (h)

(a)

(b)

0,8

18

0,7

15

0,6 12

PCE (%)

0,5

FF

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0,4 0,3

9 6

0,2

TiO2

3

TiO2

0,1



0,0 20

40

60

80

20

100 120 140 160 180 200

40

60

80

100 120 140 160 180 200

Aging time (h)

Aging time (h)

(c)

(d)

Figure 6 Stability study of reference and porphyrin-modified devices: evolution of (a) Jsc, (b) Voc, (c) FF and (d) PCE vs time of non-encapsulated PSCs under ambient conditions.



4.0

TiO2

Absorbance (a. u.)

3.5 3.0 2.5 2.0 1.5 1.0

Day 1 Day 60

0.5 0.0 450

500

550

600

650

700

750

800

850

Wavelength (nm)

(a) 4.0

(b)


Absorbance (a. u.)

3.5 3.0 2.5 2.0 1.5 1.0

Day 1 Day 60

0.5 0.0 450

500

550

600

650

700

750

800

850

Wavelength (nm)

(c)

(d) TiO2

Day 60


(110)

Day 60

(220) (220) (110) PbI2 PbI2

Day 1 (110)

Intensity

(310)

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 42

(310)

(330)

(200) (110)

Day 1 (220)

(220)

PbI2 10

(310)

(200) 15

20

25

30

35

40

45

(310)

PbI2

(330) 50

55

60

10

(330)

(200) 15

20

25

30

35

40

2xθ (deg)

2xθ (deg)

(e)

(f)

45

50

55

60

Figure 7 (a) and (c) UV-visible absorption spectra and sample photographs (inset) of perovskite films grown on as-deposited and ZnPtriazine(gly)2-modified TiO2 taken 1 and 60 days after deposition. SEM images of perovskite films grown on (b) as-deposited and (d) ZnPtriazine(gly)2-modified TiO2 taken 60 days after deposition. XRD patterns of perovskite films frown on (e) as-deposited and (f) ZnPtriazine(gly)2-modified TiO2 taken 1 and 60 days after deposition. The peak at 37o is ascribed to FTO.


Page 41 of 42

10000

TiO2 TiO2/ZnPtriazine(gly)2 1000

100

200

400

600

PL counts at 788 nm

Integrated Raman Signal (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


800 -1

Raman Frequency (cm )

10

Noise Level

10000


TiO2

1000

0.1 day 1 day 10 days

0.1 day 1 day 10 days 200 days (I) 200 days (P)

100 1 0.1

1

10

100

0

Air Exposed Duration (Days)

50

100

150

Exposure Time (sec)

(a)

(b)

Figure 8 (a) Integrated PbI2 Raman signal vs time of exposure in ambient air for perovskite films coated on as-deposited and porphyrin-modified TiO2 substrates. Inset shows a typical recorded Raman spectrum. (b) Evolution of the PL signal above 788 nm vs time for perovskite films coated on as-deposited and porphyrin-modified TiO2 films aged up to 10 days and a porphyrin-modified TiO2 film aged for 200 days where two regions are monitored either with negligible or very strong signal. (c,f) Optical images (d,g) Raman maps of the integrated PbI2 Raman signal and (e,h) combined optical and Raman views of the 200 days aged perovskite films coated on as-deposited (top: c-e) and porphyrin-modified TiO2 (bottom: f-h) films (I: Intact: P: PbI2 covered areas). 41 ACS Paragon Plus Environment


TOC


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Triazine-Substituted Zinc Porphyrin as an Electron ... - ACS Publications

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