Zinc PorphyrinâEthynylaniline Conjugates as Novel Hole-Transporting

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Zinc Porphyrin#Ethynylaniline Conjugates as Novel Hole-Transporting Materials for Perovskite Solar Cells with Power Conversion Efficiency of 16.6% Hsien-Hsin Chou, Yu-Hsien Chiang, Ming-Hsien Li, Po-Shen Shen, Hsiang-Jung Wei, Chi-Lun Mai, Peter Chen, and Chen-Yu Yeh ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.6b00432 • Publication Date (Web): 13 Oct 2016 Downloaded from http://pubs.acs.org on October 17, 2016

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ACS Energy Letters

Zinc Porphyrin‒Ethynylaniline Conjugates as Novel Hole-Transporting Materials for Perovskite Solar Cells with Power Conversion Efficiency of 16.6% Hsien-Hsin Chou,† Yu-Hsien Chiang,‡ Ming-Hsien Li,‡ Po-Shen Shen,‡ Hsiang-Jung Wei,† ChiLun Mai,† Peter Chen*,‡ and Chen-Yu Yeh*,†

Department of Chemistry and Research Center for Sustainable Energy and Nanotechnology,

National Chung Hsing University, Taichung 402, Taiwan

Department of Photonics and Research Center for Energy Technology and Strategy (RCETS),

National Cheng Kung University, Tainan 701, Taiwan

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (C.-Y. Yeh). E-mail: [email protected] (P. Chen)

ACS Paragon Plus Environment

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ABSTRACT. New zinc porphyrins Y2 and Y2A2 have been utilized in perovskite solar cells (PSCs) specifically as hole-transporting materials (HTMs) rather than photosensitizers. The combination of MAPbI3 as photosensitizer and porphyrins as HTMs is potential alternative to well-known MAPbI3/Spiro-OMeTAD hybrids owing to high performance and versatility toward molecular engineering of porphyrin families. A high efficiency of 16.60% is achieved by n-butyl tethered Y2 HTM (VOC = 0.99 V; JSC = 22.82 mA cm-2) which is comparable to that of SpiroOMeTAD of 18.03% (VOC = 1.06 V; JSC = 22.79 mA cm-2). Both materials possess similar HOMO level and same order of magnitude of hole-mobility at 10-4 cm2 V-1 s-1. The slightly poorer performance of 10.55% (VOC = 1.01 V; JSC = 17.80 mA cm-2) is obtained for n-dodecyl tethered Y2A2 HTM. This is believed to stem from more surface pinholes while deposited on perovskite leading to an order of magnitude slower mobility.

TOC GRAPHICS


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Harvesting solar energy as a promising solution to growing energy crisis of the community is undoubtedly one of the attractive objectives in the new century. Perovskite-based solar cells (PSCs) have shown great potential to surmount over other organic and hybrid solar cells as the power conversion efficiency of PSCs has been dramatically improved from 3.8% to over 20% in the past few years.1,2 With ABX3 type tetragonal crystal structure where A, B and X typically represent small molecular cation, lead or tin, and halide, respectively, the organometal halide perovskite, e.g., CH3NH3PbI3 or MAPbI3, is fascinating for several features like lower manufacturing costs, long electron-hole diffusion length,3,4 tunable bandgap,5-7 tolerance toward solution process,8 extremely low exciton binding energy,9,10 suppressed charge recombination and hybrid nature to be operated as p- or n- type materials.3,4 The broad absorption at UV-vis region with bandgap typically of 1.5 eV for CH3NH3PbI3 and HOMO and LUMO levels at -5.43 eV and -3.93 eV, respectively,11 make perovskite materials promising photosensitizers for semiconductor solar cells. While generalized p-i-n or p-n junction of PSCs employs perovskite as n-type conductor, the choice of a hole-conductor requires suitable energy level and good hole-mobility for rapid transfer of holes from perovskite and suppressed charge recombination. It is a great advantage to graft the concept of arylamine-based hole-transporting materials (HTMs) designed for organic light-emitting diodes and organic field-effect transistors12-14 to PSCs because of their good thermal properties and hole-mobility. 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'spirobifluorene (Spiro-OMeTAD)15-17 is a well-known HTM characterized as spiro framework and multiple electron-rich arylamine substituents. Introducing Spiro-OMeTAD as alternative solid-state HTM to I-/I3- electrolytes18 unlocks the possibility of PSCs toward valid candidates for next-generation solar cells.11 Careful engineering of PSC devices reaches high conversion


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efficiencies of 19.3% and 20.2% using Spiro-OMeTAD and its cyclopentadithiophene analogue, respectively.19,20 Addition of Li-TFSI is compulsory for Spiro-OMeTAD due to its poor holemobility in pristine form. However, this chemical oxidation process eventually leads to erosion of perovskite layer.16,21 In addition, the less amenability toward functionalization,22,23 lengthy and tedious synthetic route originated from the spiro backbone as well as the involvement of hazardous n-butyllithium during traditional synthesis brings about certain obstacle to practical application of Spiro-OMeTAD. Considerable efforts therefore focus on developing alternative hole-transporters with optimized synthetic protocols. Judicious molecular engineering has also successfully produced several high performance HTMs with high carrier mobility and stability via either modification of spiro-based materials such as fluorine-9,9'-xanthenes,24,25 bifluorenylidene26 or extensive integration of alternative core skeletons like triphenylamines,27 carbazoles,28-31 triptycenes,32 biphenyls,29,33-35 thiophenes,36-40 triazines,41 pyrenes42 and heteroacenes.43,44 As an advantage, the HTM layer is supposed to be colorless since any UV-vis light absorption of HTM would affect the light-harvesting efficiency of perovskite layer. In this regard, porphyrin derivatives would definitely be removed from the wish list for its superior light-harvesting properties. Questions are raised as the following. Does the light-harvesting properties of porphyrins deteriorate the efficiency of PSCs? Can porphyrins carry holes efficiently in PSCs? As a matter of fact, synthetic zinc porphyrin dyes have experienced fruitful achievements as highly efficient photosensitizers for dye-sensitized solar cells (DSCs).45-47 Zinc porphyrins such as GY5048 and SM31549 with proper design of donor and acceptor/anchoring groups have shown record high conversion efficiency of 12.75% and 13.0%. While as small-molecule holeconducting media, the zinc porphyrin-EWG conjugates,50-54 where EWG denotes to electron-


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withdrawing groups like rhodanine,53 diketopyrrolopyrrole50,54 and dicyanovinyl groups,52 also show promising performance (η = 4 - 8%) for bulk-heterojunction photovoltaics with holemobility at the range between 10-4 - 10-6 cm2 V-1 s-1.50-55 Although these porphyrin derivatives present good ability to carry positive charges in both types of solar cells, they work basically as efficient light-harvesters which lead to the high performance of the devices. Nevertheless, the application of porphyrins exclusively as a hole-transporter rather than a light-harvester in photovoltaic devices is still found absent. Herein we have devised novel zinc porphyrins Y2 and Y2A2 (see Figure 1) and proved their potential application as hole-transporting materials for high performance perovskite-based solar cells. The UV-vis region of incident light is found to be nicely absorbed by perovskite layer and only limited amount of visible light approaches the holetransporting layer. As a result, the porphyrin-based hole-transporters can be regarded as working in the dark without harvesting light. During the period of our study on these new porphyrin HTMs, a similar system using natural chlorophyll derivatives has recently shown a power conversion efficiency (PCE) of 11.44%.56 To the best of our knowledge, however, this is the best performing porphyrin-based solar cells with PCE of >16%. Both molecular structures of Y2 and Y2A2 consist of meso-5,15-bis(ethynylaniline)porphyrin backbone bearing bilateral alkyl chains. Bridging of ethynyl groups between porphyrin core and anilines ensures sufficient electronic communication between each other. The lateral alkyl chains are found to increase the solubility and affect the film morphology of porphyrin materials. These materials are designed to be structurally simple and symmetric such that the synthesis of the final compounds involves only simple condensation, bromination, and Sonogishira coupling57 steps starting from commercially available chemicals and reagents (detailed in Supporting Information). Thermogravimetric analysis (TGA) shows only 5% weight loss of Y2 and Y2A2 at


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temperature of as high as 384 oC and 366 oC, respectively, indicating fairly stable structure of porphyrins (Figure S1 in Supporting Information). UV-vis absorption spectroscopy has revealed the difference in intermolecular interactions and competitive light-harvesting with perovskite for Y2-series porphyrins (Figure 2 and Table 1). Both Y2 and Y2A2 show almost identical absorption in THF owing to the same structural backbone (see also Figure S2 and Table S1 in Supporting Information). Two absorption bands were observed at ca. 472 nm and ca. 684 nm characterized as Soret and Q band, respectively (Figure 2a). Nevertheless, Y2 as thin-film shows both Soret and Q bands red-shifted and significantly broadened (with FWHM of ca. 3000 cm-1), indicating stronger intermolecular interaction probably originated from aggregation of porphyrin molecules. For thin film of longchain tethered Y2A2, only moderate broadening (with FWHM of ca. 1500 cm-1) of the absorption bands and a shoulder at ca. 650 nm accompanied with Q band were observed. The discrepancy between two porphyrins in condensed phase might be indicative of different surface morphology while deposited on perovskite layer. Comparing with the Spiro-OMeTAD that absorbs photons only in the UV region, porphyrin-based HTMs may participate in the light harvesting process inside the solar cells. To address this issue, we measured the UV-vis absorption spectra for perovskite film with and without Y2, which are shown in Figure 2b. It is clear that there is no significant difference for the absorption from 350 to 640 nm due to the saturated absorption by the perovskite film, whereas longer wavelength absorption (640 ‒ 750 nm) has minor contribution from the absorption of Y2. Therefore, the porphyrin-based HTM is regarded as having limited effect in terms of the light absorption competition with perovskite. The fluorescence spectra for both porphyrins in principle follow Kasha’s rule with small Stokes shift both in solution and condensed phase (337-534 cm-1), showing relatively smaller energy


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required for geometrical reorganization at excited state (Figure S2 and Table S1). Cyclic voltammograms reveal a reversible first oxidation potential E1/2(ox) at ca. +0.12 V referenced to Fc/Fc+ for both porphyrins, which is in a proximity of that for Spiro-OMeTAD (+0.118 V vs Fc/Fc+)58 (see Figure S3 and Table S2). Consequently, Y2-series materials share comparable HOMO level with Spiro-OMeTAD at -5.22 eV,59,60 leading to a large energy difference with LUMO of perovskite at -3.93 eV.11 Figure 3a shows typical device configuration of perovskite solar cells with porphyrin HTMs as imaged by the cross-sectional scanning electron microscopy (SEM). The perovskite capping layer/mesoporous TiO2 layer with 550 nm thickness is deposited with 70 nm of Y2 HTM and 60 nm of gold electrode via spin-coating and thermal evaporation, respectively. The effective holeextraction ability of porphyrin HTMs is evident in their photoluminance (PL) spectra (Figure 3b). All the PL for perovskite is quenched very efficiently in the presence of HTMs ‒ either Spiro-OMeTAD or Y2-series porphyrins. This phenomenon indicates prominent ability of charge separation at perovskite interface for Y2-series porphyrins. The energy diagram of the device with different HTMs is illustrated in Figure 4. The HOMO of Y2 and Y2A2 are -5.25 eV and -5.10 eV, respectively, according to ultraviolet photoelectron spectroscopy measurements (Figure S4). These values are very close to that for Spiro-OMeTAD (-5.22 eV) so that they would be expected to exert high open-circuit voltage (VOC) of ca. 1 V like Spiro-OMeTAD does. Additionally, the LUMO levels for Y2 and Y2A2 are at -3.39 eV and 3.42 eV, respectively. These are also higher than that of perovskite layer (-3.93 eV) such that the possible current leakage from active layer toward gold electrode can be largely retarded (see Table S2). The current density-voltage (J-V) characteristics of devices with different HTMs are measured under AM 1.5G 1 Sun (100 mW cm-2) intensity with mask aperture size of 0.2 cm2


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(Figure 5a). In fact, as shown in Table 2 for their best performing parameters, the VOC of devices using Y2 and Y2A2 are 0.99 V and 1.01 V, respectively, only slightly smaller than that using Spiro-OMeTAD (1.06 V). In addition, the Y2 device has almost identical short-circuit current (JSC) of 22.82 mA cm-2 and fill factor (FF) of 73.34%, comparable to Spiro-OMeTAD (JSC = 22.79 mA cm-2; FF = 74.39%), leading to PCE of 16.60% for the former and 18.03% for the later. To the best of our knowledge, our result records the best performing porphyrin-based hybrid/organic solar cells with PCE >16%, not to say the first verification of porphyrin HTM for PSCs. It is noted that a more pronounced hysteresis effect was observed for Y2-based PSC rather than that for Spiro-OMeTAD (Figure S5). The Y2A2-based device, on the other hand, has lower PCE of 10.55% with JSC of 17.80 mA cm-2 and FF of 58.69%. The histograms of PCE and statistical average of parameters for 50 porphyrin HTM-based devices are given in Figure S6 and Table S3, respectively. On average, the device efficiency made of Y2 (14.00%) is higher than that of Y2A2 (9.56%) with notable differences in photocurrent. In order to understand the effect of hole-mobility on the device performance, we performed the space charge limited current (SCLC) measurement,61 a common and useful method to evaluate the mobility of a hole in organic semiconductors,62,63 following the Mott–Gurney law, J(V) = (9/8)εε0µd-3V2. The fitting data of J-V curve for HTMs sandwiched between gold electrode and FTO substrate is shown in Figure S7. The trend in hole-mobility is Spiro-OMeTAD (9.46 × 10-4 cm2 V-1 s-1) > Y2 (2.04 × 10-4 cm2 V-1 s-1) > Y2A2 (1.53 × 10-5 cm2 V-1 s-1), which is in good relationship with FF of the devices. Note also the comparable hole-mobility of Y2 with reported spiro-analogous X6024 (1.9 × 10-4 cm2 V-1 s-1). Comparing Y2 with Y2A2, the difference of the hole-mobility may attribute to the length of bilateral alkyl chains which increase the intermolecular distance and hamper the hole hopping.


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SEM images showing the morphology of HTMs (Y2 and Y2A2) on perovskite film apparently encompass some pinholes on the surface (Figure S8). The existence of pinholes suggests possible exposure of perovskite layer toward the electrode without proper hole-transporting layer. Minor pinholes on surface are found for Y2 as compared to Y2A2, indicating increased recombination for the later between electrons from perovskite and holes from gold electrode. Also, the pinholes in HTMs retard charge-transport leading to the low photocurrent and FF.23,64 This also explains statistically lower VOC and JSC for Y2A2 (see Table S3). Figure 5b shows comparable incident photon-to-electron conversion efficiency (IPCE) spectra for Y2 and Spiro-OMeTAD over the entire UV-vis region (350 ~ 800 nm). This indicates that both HTMs exhibit superior charge extraction/collection as well as reduced recombination of accumulated charge within perovskite layer. Again, much worse performance in IPCE for Y2A2 results from the lower hole-mobility and hindered charge transport. Although Y2A2 shows slightly higher steady-state PL quenching ability than the others (Figure 3b), we cannot exclude the possible non-radiative process during the charge extraction between the perovskite and Y2A2 interface, which contributes the lower PCE. Another interesting observation is the additional absorption by porphyrin Y2 at around 700 nm (Figure 2b) does not lower the IPCE and photocurrent since the photons of around 700 nm that are not fully absorbed and penetrate through perovskite layer could possibly be reflected from metal back contact and re-harvested by perovskite layer again. Another possibility is the slightly inefficient process for photon-induced electron-hole pairs to separate and reach the perovskite/HTM interface due to low dielectric constant typically occurring in organic semiconductors.63,65 Finally, preliminary stability tests indicate that the perovskite cell made with Y2 has better moisture resistance than that made with Spiro-OMeTAD. The photovoltaic performances of Y2-


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device under ambient storage decay much slower as compared to the Spiro-OMeTAD device (Figure S9). This substantiates another merits for the use of porphyrin-based HTM. In summary, we have designed and prepared new symmetric ethynylaniline-substituted porphyrins Y2 and Y2A2 and tested their application as hole-transporting materials for perovskite solar cells (PSCs). Unlike generally used in dye-sensitized solar cells for porphyrin sensitizers, our porphyrins Y2 and Y2A2 were utilized not to harvest incident light but to function as hole-transporter. These materials are structurally simple and easy to be synthesized. The power conversion efficiencies of PSCs with Y2, Y2A2 and Spiro-OMeTAD as HTMs are 16.60%, 10.55% and 18.03%, respectively. The films of porphyrin HTMs presented in this work exhibit good hole-transporting ability, especially in the case of Y2. The low HOMO level, high hole-mobility as well as less observed surface pinholes while deposited on perovskite lead to open-circuit voltage and short-circuit current of Y2 comparable to those of Spiro-OMeTAD. So far we cannot clarify if there exists any other beneficial effects for porphyrin-based HTMs except their efficient hole-transporting property. Nevertheless, unlike spiro and most organic framework, the total 13 positions on peripheral (4 meso and 8 beta positions) and coordination center of a porphyrin encompass high versatility of structural modification such that future finetuning of photophysical, electrochemical and charge transporting properties become feasible. Considering the absence of porphyrin-based HTMs for use in PSCs, this work opens a new paradigm of hole-transporter based on porphyrin families.


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O

O

N

N

N Zn N N

N

N Zn N N

N

N

N Y2A2

Y2 O

O

Figure 1. Molecular structures of hole-transporting materials in this study.

(a)

(b) Y2 in THF Y2A2 in THF Y2 film Y2A2 film

1.0 0.8

4 Absorbance

Normalized Intensity (a.u.)

0.6 0.4

Perovskite Perovskite+Y2

3 2 1

0.2 0.0

0 400

500

600

700

800

400

500

Wavelength (nm)

600

700

800

Wavelength (nm)

Figure 2. Absorption spectra of (a) Y2 and Y2A2 in THF and as thin films. (b) TiO2/perovskite films with and without Y2.

(b)

PL Intensity (a.u.)

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4

3

with Spiro-OMeTAD with Y2 with Y2A2 without HTM

2

1

0 600

650

700

750

800

850

900

Wavelength (nm)


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Figure 3. (a) Cross-sectional SEM image of perovskite solar cell device with Y2 HTM. (b) Photoluminescence spectra perovskite thin-films with and without HTM.

Figure 4. Energy levels of each layer in perovskite solar cells.

0

(b) 80

Spiro-OMeTAD Y2 Y2A2

-5 -10

60 IPCE (%)

5

-2

(a) Current Density (mA cm )

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-15

40 Spiro-OMeTAD Y2 Y2A2

20

-20 -25 0.0

0

0.2

0.4

0.6

0.8

1.0

1.2

400

500

Voltage (V)

600

700

800

Wavelength (nm)

Figure 5. (a) J-V and (b) IPCE plots for PSCs with HTMs.

Table 1. Photophysical and electrochemical data for HTM materials

Y2

λabsa

FWHMa,b

λabsc

FWHMb,c

E1/2(ox),d

EHOMO,e

(nm)

(cm-1)

(nm)

(cm-1)

(V vs Fc/Fc+)

(eV)

472, 684

1181

487, 654, 694, 722

2967

0.12

-5.22


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Y2A2

473, 685

1316

487, 658, 720

1579

0.11

-5.21

a

Absorption spectra of sample solution were measured in THF at 25oC. bFWHM is the full width at half-maximum height. Values indicated are for Soret bands. cThin-film absorption of the samples on FTO glass. dE1/2(ox) denotes to first oxidation potentials of 1 × 10-3 M sample solution in THF containing 0.1 M [(n-Bu)4N]PF6 as supporting electrolyte. Potentials are repoted vs ferrocene/ferrocenium (Fc/Fc+). eEHOMO denotes to HOMO energy in eV calculated based on the formula: EHOMO = ‒ (5.1 + E1/2(ox)).

Table 2. Photophysical and electrochemical data for HTM materials VOC

JSC

FF

PCE

Rs

(V)

(mA cm-2)

(%)

(%)

(Ω)

Y2

0.99

22.82

73.34

16.60

18.93

Y2A2

1.01

17.80

58.69

10.55

74.78

Spiro-OMeTAD

1.06

22.79

74.39

18.03

23.34

ASSOCIATED CONTENT Supporting Information. Experimental details, photophysical, electrochemical, thermal analysis and SCLC measurements and device measurements data, and 1H and 13C NMR spectra (PDF).

AUTHOR INFORMATION Notes †

H.-H. Chou and Y.-H. Chiang contributed equally to this work.

The authors declare no competing financial interest.


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ACKNOWLEDGMENT The authors thank the financial support for this work from the Ministry of Science and Technology (MOST) in Taiwan with Grant No. MOST 104-2119-M-005-MY3, MOST 1032221-E-006-029-MY3 and MOST 105-2623-E-006-002-ET.

REFERENCES (1) Loi, M. A.; Hummelen, J. C. Hybrid Solar Cells: Perovskites under the Sun. Nature Mater. 2013, 12, 1087-1089. (2) Green, M. A.; Ho-Baillie, A.; Snaith, H. J. The Emergence of Perovskite Solar Cells. Nature Photon. 2014, 8, 506-514. (3) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber. Science 2013, 342, 341-344. (4) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Long-range Balanced Electron- and Hole-transport Lengths in Organic-inorganic CH3NH3PbI3. Science 2013, 342, 344-347. (5) Stoumpos, C. C.; Malliakas, C. D.; Kanatzidis, M. G. Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-infrared Photoluminescent Properties. Inorg. Chem. 2013, 52, 9019-9038. (6) Mosconi, E.; Amat, A.; Nazeeruddin, M. K.; Grätzel, M.; De Angelis, F. First-Principles Modeling of Mixed Halide Organometal Perovskites for Photovoltaic Applications. J. Phys. Chem. C 2013, 117, 13902-13913. (7) Hao, F.; Stoumpos, C. C.; Chang, R. P.; Kanatzidis, M. G. Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells. J. Am. Chem. Soc. 2014, 136, 8094-8099. (8) Zhao, Y.; Zhu, K. Solution Chemistry Engineering Toward High-Efficiency Perovskite Solar Cells. J. Phys. Chem. Lett. 2014, 5, 4175-4186. (9) D'Innocenzo, V.; Grancini, G.; Alcocer, M. J.; Kandada, A. R.; Stranks, S. D.; Lee, M. M.; Lanzani, G.; Snaith, H. J.; Petrozza, A. Excitons Versus Free Charges in Organo-lead Tri-halide Perovskites. Nature Commun. 2014, 5, DOI:10.1038/ncomms4586. (10) Lin, Q.; Armin, A.; Nagiri, R. C. R.; Burn, P. L.; Meredith, P. Electro-optics of Perovskite Solar Cells. Nature Photon. 2014, 9, 106-112. (11) 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. et al. Lead Iodide Perovskite Sensitized All-solidstate Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, DOI: 10.1038/srep00591.


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(43) Liu, Y.; Hong, Z.; Chen, Q.; Chen, H.; Chang, W. H.; Yang, Y. M.; Song, T. B.; Yang, Y. Perovskite Solar Cells Employing Dopant-Free Organic Hole Transport Materials with Tunable Energy Levels. Adv. Mater. 2015, 28, 440-446. (44) Bi, D.; Mishra, A.; Gao, P.; Franckevičius, M.; Steck, C.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Bauerle, P.; Grätzel, M.; Hagfeldt, A. High-Efficiency Perovskite Solar Cells Employing a S,N-Heteropentacene-based D-A Hole-Transport Material. ChemSusChem 2016, 9, 433-438. (45) Urbani, M.; Grätzel, M.; Nazeeruddin, M. K.; Torres, T. Meso-Substituted Porphyrins for Dye-Sensitized Solar Cells. Chem. Rev. 2014, 114, 12330-12396. (46) Higashino, T.; Imahori, H. Porphyrins as Excellent Dyes for Dye-sensitized Solar Cells: Recent Developments and Insights. Dalton. Trans. 2015, 44, 448-463. (47) Li, L. L.; Diau, E. W. Porphyrin-Sensitized Solar Cells. Chem. Soc. Rev. 2013, 42, 291304. (48) Yella, A.; Mai, C.-L.; Zakeeruddin, S. M.; Chang, S.-N.; Hsieh, C.-H.; Yeh, C.-Y.; Grätzel, M. Molecular Engineering of Push-Pull Porphyrin Dyes for Highly Efficient Dye-Sensitized Solar Cells: The Role of Benzene Spacers. Angew. Chem. Int. Ed. 2014, 53, 2973-2977. (49) Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-Sensitized Solar Cells with 13% Efficiency Achieved Through the Molecular Engineering of Porphyrin Sensitizers. Nature Chem. 2014, 6, 242-247. (50) Qin, H.; Li, L.; Guo, F.; Su, S.; Peng, J.; Cao, Y.; Peng, X. Solution-processed Bulk Heterojunction Solar Cells Based on a Porphyrin Small Molecule with 7% Power Conversion Efficiency. Energy Environ. Sci. 2014, 7, 1397-1401. (51) Sharma, G. D.; Zervaki, G. E.; Angaridis, P.; Coutsolelos, A. G. New Solution Processed Bulk-heterojunction Organic Solar Cells Based on a Triazine-bridged Porphyrin Dyad as Electron Donor. RSC Adv. 2014, 4, 50819-50827. (52) Kumar, C. V.; Cabau, L.; Koukaras, E. N.; Palomares, E. J.; Sharma, G. D. Synthesis, Optical and Electrochemical Properties of A-π-D-π-A Porphyrin and its Application as Electron Donor in Efficient Solution Processed Bulk Heterojunction Solar Cells. Nanoscale 2015, 7, 179189. (53) Gao, K.; Xiao, L.; Kan, Y.; Yang, B.; Peng, J.; Cao, Y.; Liu, F.; Russell, T. P.; Peng, X. Solution-processed Bulk Heterojunction Solar Cells Based on Porphyrin Small Molecules with Very Low Energy Losses Comparable to Perovskite Solar Cells and High Quantum Efficiencies. J. Mater. Chem. C 2016, 4, 3843-3850. (54) Gao, K.; Li, L.; Lai, T.; Xiao, L.; Huang, Y.; Huang, F.; Peng, J.; Cao, Y.; Liu, F.; Russell, T. P. et al. Deep Absorbing Porphyrin Small Molecule for High-performance Organic Solar Cells with Very Low Energy Losses. J. Am. Chem. Soc. 2015, 137, 7282-7285. (55) Zhou, L.; Xu, Z. X.; Zhou, Y.; Feng, Y.; Zhou, X. G.; Xiang, H. F.; Roy, V. A. Structurecharge Transport Relationship of 5,15-Dialkylated Porphyrins. Chem. Commun. 2012, 48, 51395141. (56) Li, M.; Li, Y.; Sasaki, S. I.; Song, J.; Wang, C.; Tamiaki, H.; Tian, W.; Chen, G.; Miyasaka, T.; Wang, X. F. Dopant-Free Zinc Chlorophyll Aggregates as an Efficient Biocompatible Hole Transporter for Perovskite Solar Cells. ChemSusChem 2016, 10.1002/cssc.201601069.


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Novel porphyrin derivatives are developed to function as very efficient hole-transporting materials rather than photosensitizers for the applications in perovskite-based solar cells. 95x95mm (300 x 300 DPI)


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