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Hot-air assisted fully air-processed barium incorporated CsPbI2Br perovskite thin films for highly efficient and stable all-inorganic perovskite solar cells. Sawanta S Mali, Jyoti V. Patil, and Chang Kook Hong Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b02277 • Publication Date (Web): 01 Aug 2019 Downloaded from pubs.acs.org on August 1, 2019
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Nano Letters
Hot-air assisted fully air-processed barium incorporated CsPbI2Br perovskite thin films for highly efficient and stable all-inorganic perovskite solar cells Sawanta S. Mali, Jyoti V. Patil and Chang Kook Hong* Polymer Energy Materials Laboratory, School of Advanced Chemical Engineering, Chonnam National University, Gwangju, South Korea-61186 Supporting Information Placeholder ABSTRACT: Replacement of conventional organic cations by thermally stable inorganic cations in perovskite solar cells (PSCs) is one of the promising approach to make thermally-stable photovoltaics. However, conventional spin-coating and solventengineering processes in controlled inert atmosphere hampers the upscaling. In this study, we demonstrated, a dynamic hot-air (DHA) casting process to control the morphology and stability of all inorganic PSCs which is processed in ambient condition and free from conventional harmful antisolvents. Furthermore, CsPbI2Br perovskite was doped with barium (Ba2+) alkaline earth metal cations (BaI2:CsPbI2Br). This DHA method facilitates formation of uniform grain and controlled crystallization that makes a stable all-inorganic PSCs which enables to intact the black -phase in ambient condition. The DHA processed BaI2:CsPbI2Br perovskite photovoltaics shows the champion power conversion efficiency (PCE) of 14.85 % (reverse scan) for small exposure area 0.09 cm2 and 13.78% for large area 1 x 1 cm2 with excellent reproducibility. Interestingly, the hot-air processed devices retain >92 % of the initial efficiency after 300 hours. This DHA method facilitates a wide processing window for up-scaling the allinorganic perovskite photovoltaics. KEYWORDS: All-inorganic perovskites, CsPbI2Br perovskites, hot-air method, barium incorporation, stability All-inorganic lead-halide perovskites exhibiting an excellent thermal stability than conventional organic-inorganic mixed halide perovskite. Typically, cesium based mixed-halide (CsPbX3) perovskite show excellent efficiency due to it optimum band gap revealed long-term operational stability. Furthermore, this CsPbX3 is not only solar cell application but also can be used in thermochromic switchable optoelectronics.[1] The stability of this unstable -CsPbI3 perovskite has been improved by bifunctional phenyltrimethylammonium bromide (PTABr) post-treatment with 17.06 % power conversion efficiency.[2] However, the poor stability of all-inorganic cesium-lead halide based perovskites is main drawback need to tackle via alternative method with unique perovskite composition. Conventional solvent-engineering process or controlled grain growth of perovskite crystal is based on first nucleation followed by crystal grain growth. However, it is difficult to control the homogenous nucleation centers in order to control the grain size and uniformity. Furthermore, the processing window for solvent engineering process is too narrow, therefore it is difficult to obtain successive reproducibility. Although, solvent engineering process holds a peak PCE, antisolvents such as toluene or chlorobenzene are randomly spread on to substrate due to centrifugal force during spinning which limits the large area fabrication caused by irregular film thickness. Therefore, implementation of an alternative ecofriendly method for uniform
and highly stable perovskite deposition technique is needed. So far, number of alternative physical techniques including vacuum-flash for conventional organic cation based perovskites,[3] cryogenic assisted,[4] spray-deposition,[5,6] hot-air (including gasquenching),[7-9] slot-die,[10,11] brush-painting,[12] electrodeposition,[13] pressure-processing,[14] gas-assisted method,[15-18] soft-cover deposition,[19] flash-annealing,[20] and N2 air-blading[21] have been used for organic-inorganic hybrid perovskite absorber. However, all these methods were processed either in inert atmosphere or nitrogen-air blowing during deposition. Furthermore, the performance for small as well as large area is still limited. Therefore, this fully-air processed hot-air assisted method will offers a great opportunity to upscale all inorganic perovskite solar cells (AI-PSCs) technology towards commercialization. In case of all-inorganic perovskites, although alternative methods such as post-air flow, co-evaporation and vacuum flash has been used but still solvent engineering process holds a peak efficiency which is processed in nitrogen atmosphere. The previous work suggest that, the CsPbI2Br film quality, defect-free crystallinity and thickness dominates the photovoltaic performance. Nowadays, obtaining >1 m grain size for CsPbI2Br film by solvent-engineering method is easy but difficult to obtain vertical growth in same dimension. Recently, temperature assisted (>200 nm)[22] and precise growth controlling by gradient thermal annealing (GTA) and anti-solvent (ATS) treatment (~450 nm)[23] demonstrated considerable improvement in film thickness yielded 14.81% and 16.07% PCE respectively. However, both reports used nitrogen atmosphere for deposition and obtained film thickness still limited for sufficient light harvesting. Therefore, obtaining defectfree CsPbI2Br film with desirable film thickness in open atmosphere is challenging task in AI-PSCs. Besides, for thermodynamically stable inorganic perovskite, it is necessary to make a controlled crystallization rate and dense film. Although most of the recent development of AI-PSCs has been mainly focused on different experimental strategies,[24-29] but divalent and trivalent metal ion incorporation makes them stable.[30,31] Therefore, monovalent or divalent doping in all inorganic perovskites have equal importance for making stable perovskite phase in ambient condition. Previously structural simulation of the alkaline earth metal perovskites such as MACaI3, MASrI3, and MABaI3 has been studied theoretically and suggesting the presence of stable perovskite behavior.[32-35] However, the MABaI3 exhibited a transparent conducting properties due to its high band-gap 3.3 eV.[35] From the previous study, we incorporated alkaline earth metal barium (Ba2+) in to CsPbI2Br perovskite thin films to make stable -CsPbI2Br phase for the first time.[36] With the well-established CsPbI2Br composition and we mainly focused
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on development of stable perovskite layer in ambient air condition and introduced a new dynamic hot-air assisted (DHA) (Figure 1) method instead of conventional solvent engineering process or post-annealing. All-inorganic perovskite layers having CsPbI2Br and BaI2:CsPbI2Br compositions were synthesized by blowing a hot-air during spinning of perovskite precursor. This work provides new insight for the preparation of large-area, ambient air processed highly efficient and air-stable AI-PSCs. The present method can intact the original black -phase through optimum solvent preevaporation and formation of intermediate solid-phase results into a highly uniform, air-stable pin-hole free inorganic perovskite film. Based on this assumption, we focused on the preparation of highly uniform CsPbI2Br and alkaline earth metal ion barium (Ba2+) incorporated CsPbI2Br (herein BaI2:CsPbI2Br) perovskite absorber layer by controlling the crystallization rate using hot-air blow. Importantly, all process has been carried out in an open ambient condition. Besides, this hot-air assisted method has high reproducibility due to free from conventional antisolvent treatment which is widely used applied to a precursor-coated spinning or precursor-printed substrate. In short, we can say there is lot of scope to scale up this method.
the quick DMSO evaporation and fast interaction between PbX2 and CsI to form perovskite phase. However, the hot-air method yielded homogeneous perovskite film onto mp-TiO2 substrate (Figure 1d). The SEM surface morphology of the BaI2:CsPbI2Br perovskite film deposited from DHA exhibits a substantial improvement than the conventional WHA method. This uniform film formation stem from the optimum nuclei centers and controlled DMSO solvent evaporation to form crystalline CsPbI2Br thin film from PbX2-DMSO-CsI intermediate phase as reported previously.[37] Uncovered perovskite layer on the top of the mpTiO2 scaffold have been observed for as-deposited perovskite thin, while the number of randomly distributed perovskite crystal substantially decreases for 100 °C hot-air (Figure S1, S2). This is a positive indication of formation of uniform and dense film stem from the hot-air flow. Therefore, this hot-air assisted method can be categories in to four different steps. Initially, the solvent is sprayed uniformly on to substrate due to flow-air pressure. In second step, the optimum hot-air flow can partially evaporate the DMSO solvent and formation of PbX2-DMSO-CsI intermediate phase. In third step, this pre-evaporated PbX2-DMSO-CsI intermediate phase deposited uniformly onto substrate. Finally, this pre-evaporated PbX2-DMSO-CsI intermediate phase is converted into dense and pin-hole free highly crystalline CsPbI2Br phase after annealing at 280 °C for 10 min. This intermediate PbX2-DMSOCsI phase raised from DHA process confirmed from the additional XRD peak appears at 10.12° which is absent in WHA process thin film, Figure S3.[37] The AI-PSCs devices were completed by depositing doped P3HT hole-transporting material (HTM) and 60 nm gold contacts. Figure 1e and f shows the cross-sectional SEM images of WHA and DHA processed BaI2:CsPbI2Br based devices respectively.
Figure 1. Dynamic hot air process, surface morphology and device configuration of the CsPbI2Br and BaI2:CsPbI2Br AI-PSCs. (a) Schematic illustration of DHA method (b) Optical images of perovskite thin film fabricated by different methods. Surface morphology of (c) without hot-air and (d) DHA processed at 100 oC BaI2:CsPbI2Br thin films (e) and (f) respective cross-sectional SEM images.
Since we used DMSO solvent for the complete dissolution of perovskite precursor, therefore possibility for formation of intermediate phase PbX2-DMSO-CsI complex which facilitates limited initial nuclei centers and can be determined by the specific solvent evaporation rate. Therefore, in order to achieve dense and uniform film, limited nuclei centers with controlled evaporation rate is play a vital role (Figure 1). Then deposited PbX2-DMSOCsI complex solid film was annealed at 280 °C for 10 min to form resultant highly crystalline BaI2:CsPbI2Br film. In order to compare the perovskite film with conventional method, the BaI2:CsPbI2Br thin film was also deposited without hot-air (WHA) flow from the same perovskite precursor solution. Figure 1c and d represents the top-view scanning electron micrographs (SEM) of BaI2:CsPbI2Br film deposited on FTO/c-TiO2/mp-TiO2 substrate by WHA and DHA (100 °C) respectively. From top-view SEM micrographs it is observed that the mp-TiO2 layer is not covered fully by the perovskite layer (Figure 1c) and the perovskite crystals are randomly distributed with numerous uncovered area. This is due to
Figure 2: Elemental analysis of BaI2:CsPbI2Br perovskite (a) typical scanning TEM image of the BaI2:CsPbI2Br perovskite thin film deposited on mp-TiO2; Scale bars, 50 nm. (b) Respective HAADF STEM image and (c-i) elemental distribution of BaI2:CsPbI2Br. Red: cesium; Green: lead; Yellow: iodine; Green: bromide; dark yellow: barium; yellow: titanium; Red: oxygen. Scale bars, 50 nm.
From the cross-sectional SEM images of WHA and DHA processed films, it is clearly observed that the WHA processed film contained irregular coverage of perovskite capping layer (Figure 1e). However, our DHA processed sample exhibited formation of ~530 nm thick uniform capping layer (Figure 1f). This capping
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Nano Letters layer facilitates a smooth interface between TiO2-perovskite and perovkite-P3HT. As previously discussed, it is very difficult to obtain thick and uniform CsPbI2Br perovskite layer by the conventional methods. However, with our DHA method, it is obtained a 530 nm thick film. In order investigate the Ba2+ distribution in perovskite thin film, we obtained the SEM/ energy-dispersive X-ray spectroscopy (EDS) mapping. Interestingly, our elemental mapping results revealed that the Ba2+ is homogeneously distributed throughout the perovskite film (Figure S4). In addition, we have also recorded the high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) imaging and EDS mapping to evaluate uniformity of Ba2+ distribution inside the perovskite grains. This method will help us to evaluate the Ba2+ distribution in the perovskite lattice at atomic level. The mapping results exhibited that the Ba2+ incorporated into the perovskite lattice and distributed throughout the film uniformly (Figure 2). Furthermore, the other elements are also distributed uniformly in the perovskite grains.
doublets in I(3d) and Br(3d) core level corresponds to I-Ba and BrBa bonds (Figure S5 d,e). In case of Ba2+ incorporated thin film, it is observed that, the Ba(3d) core level spectrum revealed doublet peaks of Ba(3d5/2) and Ba(3d3/2) at 780.57 and 795.9 eV corresponds to the presence of Ba. The X-ray diffraction (XRD) patterns of the CsPbI2Br and BaI2:CsPbI2Br compositions perovskite films (Figure 3a) prepared by both methods revealed the formation of alpha () perovskite phase. However, the films prepared by the hot-air method, the intensity of perovskite reflection at 2 =14.6° and 29.5° corresponding to the (100) and (200) planes have been dramatically increased than conventional process. This enhanced intensity arises from the much highly crystalline superior coverage of contiguous and compact layer of the perovskite capping layer due to DHA which is apparent from the photographs (Figure 1b). We have not observed any additional peak at 2=~10 ° for both perovskite thin films suggestion complete reaction. It is well known that the higher Ba2+ doping can effect on the (100) peak shift towards smaller scattering angles due to higher ionic radius of Ba2+ (~135 pm) than Pb2+ (~119 pm) and formation of CsPb1-xBaxI2Br phase.[35] However, we have used minimal doping concentration therefore it can effect on the (110) peak shift Figure S6a. In order to investigate in depth, we have calculated the texture coefficient (TC) of all perovskite thin films. The TC of plane represents the texture of a particular plane, whose deviation from the standard sample implies the preferred growth. The perovskite thin-film thickness is directly affecting on the texture of the perovskite material. Besides, the structural and optical properties of the CsPbI2Br based perovskite thin film and its photovoltaic performance is directly dependent on the texture of the perovskite thin film. Therefore, the texture coefficient of (100) plane is determined from the XRD spectra,[38, 39]
TC (hkl )
Figure 3 Structural, photovoltaic and stability analysis of CsPbI2Br and BaI2:CsPbI2Br based AI-PSCs (a) XRD patterns (b) Original photovoltaic performance based on -CsPbI2Br perovskite with and without the incorporation of 0.5 mol % BaI2 perovskite thin films processed at 100 oC. (c) PCE distributions for 30 DHA processed AI-PSCs devices. (d) EQE spectra for controlled and DHA processed BaI2:CsPbI2Br perovskite devices. (e) Long-term stability of AI-PSCs based on pristine and BaI2 incorporated CsPbI2Br perovskite absorber processed by DHA method monitored at 85°C without any encapsulation. All measurements were performed on un-encapsulated cells in ambient air. Color code are same for all figures.
To order to check the chemical composition and evidence of Ba2+ incorporation in CsPbI2Br perovskite thin film, we acquired the X-ray photoelectron spectroscopy (XPS), Figure S5. The survey spectra exhibited the presence all Cs, Pb, I and Br and Cs, Pb, I, Br and Ba elements respectively for CsPbI2Br and BaI2: CsPbI2Br thin films. The deconvoluted peaks corresponded to Cs(3d5/2) and Cs(3d3/2) at a binding energy (BE) 724.12 eV and 738.06 eV respectively. It is noted that, we observed a negligible shift in Cs(3d) core level spectrum after Ba2+ incorporation due to weak interaction between Cs+ and the central atom in the octahedron. The Pb(4f7/2) and Pb(4f5/2) core level peaks appear at 137.68 and 142.57 eV respectively (Figure S5c). However, we observed the additional Pb(4f7/2)-Pb(4f5/2) double orbital at lower binding energy after Ba2+ doping revealed formation of Pb-X-Ba bonds. The deconvoluted peaks of BaI2:CsPbI2Br thin film corresponded to Pb(4f7/2) and Pb(4f5/2) at 138.06 eV and 142.95 eV respectively. Besides, we observed similar additional orbital
I m (hkl ) / I 0 (hkl )
….. (1)
1 n I m (hkl ) / I 0 (hkl ) n 1
where Im(hkl) is the reflected intensity from hkl crystallographic planes in the perovskite thin film, and Io(hkl) is the standard intensity, and n is the total number of reflections measured. The TC value for a particular set of planes (hkl) is proportional to the number of grains that are oriented with this plane parallel to the surface of the perovskite film. The variation of TC (100) values for the (100) peak of all CsPbI2Br films processed by WHA and DHA method are also shown in Figure S6b. From the TC values it is clear that the DHA processed sample exhibited much higher TC value due to the higher degree of vertical orientation. Photovoltaic performance: As discussed above, we deposited all layers such as Bl-TiO2, mp-TiO2, perovskite and P3HT in ambient atmosphere. The device illumination-exposure area was fixed at 0.09 cm2 (small area 0.3 cm x 0.3 cm) and 1 cm2 (large area 1 cm x 1 cm) for the J-V measurement using indigenous shadow metal mask. Initially we varied different composition of BaI2 in CsPbI2Br perovskite thin film and studied its device performance (Figure S7, Table S1). From J-V characteristics, we found 0.5 mol % exhibited best performance. If we increase the Ba cation concentration, although we observed very dark film even after 0.5 mol % but the device performance declined sequentially. It is also noted that, in case of 2.0 mol % sample, we observed dark brown during deposition and persists initial few minutes during annealing but it becomes yellow afterwards. In case of 2.5 mol % composition, we have not observed any color change during hot-air process. While during annealing process we observed quick transformation from yellow to dark brown to light yellow. This is due to the higher concentration of BaI2 causes unreacted BaI2 or formation of a wider band-gap (Eg) (2.95-3.3 eV) phase such as ABaI2 (here, A: MA or Cs ).[32, 35, 40] Therefore we adopted 0.5 mol % for further study. Figure 3b shows the photovoltaic performance
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of AI-PSCs in reverse scan. Our conventional CsPbI2Br based AIPSCs device produces 9.34 % PCE with an open circuit voltage (VOC) of 1.087 V, current density (JSC) of 11.88 mAcm-2 and fill factor (FF) of 72.35%. Photovoltaic properties are summarized in Table 1. It is well known that, the organic hole-transporting layer (HTL) P3HT in contact with perovskite produces a low VOC due to non-radiative recombination at the perovskite/P3HT interface.[41] In addition, the perovskite grains are randomly distributed grains results in poor physical contacts that hampers efficient hole transport from the CsPbI2Br layer.[42] In contrast, our hot-air processed device exhibited the substantial increment in VOC up to 1.174 V. This is due to the improved CsPbI2Br/P3HT interface and effective hole transportation. Additionally, the FF improved up to 78.56% due to reduced recombination and the current density of the hot-air processed device improved up to 13.48 mAcm-2 yielded 12.43 % PCE due to formation of highly uniform and thick defect free overlayer. Table 1 Photovoltaic performance of CsPbI2Br and BaI2:CsPbI2Br based AI-PSCs processed by WHA and DHA method.
Perovski Method VOC JSC FF PCE te (V) (mAcm-2) (%) (%) CsPbI2Br WHA 1.087 11.88 72.35 9.34 CsPbI2Br DHA 1.174 13.48 78.56 12.43 BaI2: WHA 1.120 13.93 73.95 11.53 CsPbI2Br BaI2: DHA 1.210 15.45 79.45 14.85 CsPbI2Br In case of BaI2 doping, the conventional processed (WHA) device exhibited VOC of 1.120 V, JSC of 13.93 mAcm-2, and FF of 73.95 % yielded 11.53% PCE. On the other hand, DHA processed at 100 °C exhibited VOC of 1.210 V, JSC of 15.45 mAcm-2 and FF of 79.45% yielded 14.85 % (reverse scan) PCE which is due to improved (>530 nm) film thickness, reduced surface defects and improved carrier collection which reduces the energy loss. For the hysteresis behavior, we recorded the J-V characteristics in forward and reverse scan direction demonstrate that the best-performing BaI2 based device has PCE of 14.24% with VOC of 1.194 V, JSC of 15.56 mA cm-2 and FF of 76.58 % indicating negligible hysteresis index (Figure S8). The photovoltaic distribution of BaI2:CsPbI2Br AI-PSCs devices shown in Figure 2c, in which 30 devices obtained from controlled and hot-air devices. The statistical data analysis revealed high-reproducibility of DHA method. The external quantum efficiency (EQE) revealed DHA processed BaI2:CsPbI2Br perovskite based device exhibited >92 % EQE value while ~78% EQE value for controlled device yielding an integrated current density of 14.87 and 13.56 mAcm-2 respectively, which agrees well with our JSC value obtained from the J-V curves with negligible deviation. This EQE enhancement is due to thicker and highly uniform BaI2:CsPbI2Br layer achieved by DHA method (Figure 3d). Furthermore, in order to check the influence of environmental conditions, we have also fabricated both types of perovskite devices under inert condition (nitrogen filled glove box), as shown in Figure S9. From SEM micrographs, we observed similar irregular (for WHA) and uniform (for DHA) morphology in inert environmental condition. As shown in top-view micrographs, the DHA processed samples exhibited excellent coverage on the mpTiO2 layer. Besides, the Ba2+ doped sample exhibited better grain size with high uniformity which is may be due to the larger Ba2+ atoms incorporated in to CsPbI2Br can directly affect the colloidal seed formation in the precursor solution and alter the crystallization.[43] Therefore, Ba2+ doping can result in a more preferable orientation and superior crystallinity, inducing decreased grain boundaries with larger crystals and a smoother surface, which are extremely beneficial for improving conductivity, eliminating trap states and increasing moisture resistivity.[44] Therefore, Ba2+ doping could improve the stability of CsPbI2Br
perovskites. Furthermore, the devices prepared in glove box exhibited lower efficiency than fully-air processed devices, Figure S10, Table S2. This may be due to the our air-processed DHA method facilitates a moderate moisture accumulation at the grain boundaries which enables the improved crystallization for highquality perovskite thin films than inert environmental process.[45-47] Besides, this poor performance is also arises from the relatively higher temperature in the glove-box and large amount of DMSO vapors. Since we used hot-air gun as well as 280 oC hot-air temperature during fabrication of these devices.[48] In addition, the stability at harsh thermal stress has been monitored. For thermal stability we selected our DHA processed champion devices having CsPbI2Br, and BaI2:CsPbI2Br composition. We have not recorded any thermal-stability of WHA processed device due to poor ambient stability. The thermal stability of these devices was monitored at 85 °C in an electric oven and its normalized stability is shown in Figure 2e. When our devices maintained at 85 °C, aCsPbI2Br device showed much higher thermal stability while conventional devices show very poor stability. The DHA processed AI-PSCs devices fabricated from aCsPbI2Br maintained >90 of their initial efficiency after 400 hours, whereas the WHA devices as well as doped devices show poor efficiency within 100 hours. From stability analysis we observed the Ba2+ ion doped CsPbI2Br with DHA processed devices exhibited much higher stability than conventional CsPbI2Br (Figure S11). This is due to the synergetic effect of the DHA method and thermally stable BaI2:CsPbI2Br composition.
Figure 4 (a, b) Fluorescence-lifetime imaging microscopic (FLIM) images (80 m x 80 m, ex=470 nm) of the CsPbI2Br and 0.5 % BaI2:CsPbI2Br thin films processed by hot-air (controlled device) method. The FLIM images were analyzed using a three-exponential decay model: τavg, images constructed on the basis of the averaged photoluminescence lifetimes. (c) TRPL decay profiles for hot-air processed CsPbI2Br and BaI2:CsPbI2Br perovskite thin films.
The optical and charge-extraction behavior of the DHA processed perovskite layer was investigated by UV-vis absorption, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy (Figure 4, S12). The enhanced optical absorption revealed the vital-role of Ba2+ incorporation with DHA method (Figure S12a). The calculated lifetimes extracted from fluorescence-lifetime imaging microscopic (FLIM) images are shown in Figure 4a,b. The strong luminescence peak at nearly 650 nm of the pristine CsPbI2Br perovskite film was improved in the presence of BaI2 incorporation (Figure S12b). The TRPL life-time parameters were extracted by fitting with a bi-exponential decay function, Figure 3c.[49-52] The extracted life-time () values and weight factors (A) are summarized in Table S3. The TRPL decay profile exhibits increased PL life-times upon Ba2+ incorporation.
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Nano Letters Both the surface and bulk recombination lifetimes of pristine and Ba2+ ion incorporated CsPbI2Br film processed by DHA method was substantially prolonged from 2.01 ns to 16 ns suggesting suppression of non-radioactive recombination pathways. These results are also consistent with our improved photovoltaic performance. Further, to demonstrate the ability of this developed DHA method to upscale device, we fabricated a 1 x 1 cm2 large active exposure area devices. The J-V performance of BaI2:CsPbI2Br based AI-PSCs with 1 cm x 1 cm active area is shown in Figure 5a. Inset watermark image shows photograph of fabricated large area (1 cm x 1 cm) AI-PSC device. The one centimeter large exposure area perovskite device exhibited a VOC of 1.217 V, a JSC of 15.26 mA cm-2, and an FF of 74.25%, yielding a PCE of 13.78% in reverse scan. The forward scan exhibited a 12.54 % PCE (VOC of 1.189 V, JSC of 15.05 mAcm-2 and FF of 70.13 %) revealed minor hysteresis. For the device stability and its reliability, the stabilized output power (SPO) of the best performing devices were monitored at the maximum power tracking point at full sun illumination over 200 s as shown in Figure 5b. The steady-state photocurrent output of our champion devices exhibited a dramatic increase in the initial few seconds and reached 14.30 mA cm-2, corresponding to 13.60 % PCE for a large-area device revealed the excellent reproducibility. The constant photocurrent measurements exhibited a faster stabilizing rate, which is consistent with the fabricated DHA processed devices with a negligible density of trap sites.
Figure 6 Alkaline earth metal cation doped organic-inorganic and allinorganic PSCs.
In conclusion, we developed a simple anti-solvent free, nonvacuum, cost-effective and fully air-processed DHA method for stabilizing the black phase of CsPbX3 by using Ba2+ incorporation offers a new approach to achieve highly-stable AI-PSCs. The uniform distribution of Ba2+ incorporation into the CsPbI2Br perovskite lattice has been confirmed by STEM HAADF and XPS analysis. Among the previous alkaline earth metal doped organic/inorganic PSCs, we believe we are reporting state-of-theart efficiency (Figure 6). This DHA method for deposition of inorganic perovskite films offers a new avenue for large area fabrication, resulting in a highest VOC of 1.210 V, JSC of 15.45 mA cm-2, and FF of 79.45% yielding 14.85 % for small area (0.3 cm x 0.3 cm) and 13.78 % PCE for (1 cm x 1 cm) large active area. We believe that our promising DHA method will be an effective approach to tackle the instability issue of unstable CsPbX3 perovskite at ambient condition, and will be a step forward toward realizing higher-efficiency and large-area stable AI-PSCs.
ASSOCIATED CONTENT Supporting Information All-inorganic perovskite layer was deposited by hot-air methods and P3HT hole transporting materials was deposited by spin coating method at 3000 rpm. These details about preparation methods and Characterizations are given in Supporting information. The Supporting Information is available free of charge on the ACS Publications website.
AUTHOR INFORMATION Corresponding Author
[email protected],
[email protected] Notes The authors declare no competing financial interests.
Author contribution S.S.M. & C.K.H. contributed to the conception and design of the experiments. S.S.M. fabricated all the devices and conducted most of the characterizations. S.S.M and J.V.P. measured the EQE and UV-VIS spectra. S.S.M. and C.K.H. wrote the paper. All authors discussed the results and reviewed the manuscript.
ACKNOWLEDGMENT Figure 5 (a) J-V curve for centimeter-square size perovskite device fabricated by hot-air-assisted method. Watermark digital photograph shows the top-view of large area 1 × 1 cm2 BaI2:CsPbI2Br-based device (b) Steadystate photocurrent stability recorded at the maximum power point biased at 0.950 V and respective stabilized power conversion efficiency output.
This research was supported by the National Research Foundation of Korea (NRF) (NRF-2017R1A2B4008117) and National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2016H1D3A1909289) for an outstanding overseas young researcher. This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2018R1A6A1A03024334).
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