Fabrication of Efficient and Stable CsPbI₃ Perovskite Solar Cells through Cation Exchange Process

Abstract

and rapid increase in power conversion efficiency (PCE) to 25.2% most recently reported. [1] Inorganic lead halide perov skites have also attracted attention with the number of research work and demon strated efficiencies constantly on the rise [2] due to the elimination of organic cat ions and tolerance to higher processing temperatures.Among inorganic halide perovskites, CsPbI 3 has gained popularity due to the optical bandgap of 1.72 eV, which is suit able for tandem devices combining with either silicon or low bandgap perovskite solar cells. Although similar bandgap could also be obtained from the organicinorganic mixed halide perovskite by tuning the halide composition, halide segregation could be a source of photo instability. Hence, achieving stable and highly efficient CsPbI 3 PSCs is important and meaningful. [2] Phase instability has been the main challenge of CsPbI 3 cells, due to transition to the undesirable nonperovskite yellow phase (δCsPbI 3 ). [3,4] To stabilize the CsPbI 3 and achieve the desirable photoactive perovskite black phase albeit orthorhombic (γCsPbI 3 ) [5] and to improve the PSC perfor mance, different approaches have been used such as replacing iodide with bromide to form CsPbI 2 Br and CsPbIBr 2 [6-12] but introduces complication such as bandgap increase and halide segregation. [7] Other strategies for stabilizing CsPbI 3 which are also effective in improving cell performance include the use of dimethyl sulfoxide (DMSO) introducing intermediate phase for perovskite formation, [13,14] reducing grain size, [15] incorporating other metallic element to the B site in the ABX 3 perovskite [16,17] and the use of bulky organic cations on top of perovskite to pas sivate the device, [18][19][20][21][22][23] resulting in the highest PCE of 17.1%. [24] Recently, "HPbI 3 " was used to replace PbI 2 in the precursor when fabricating CsPbI 3 perovskite, [23][24][25] resulting in the for mation of αCsPbI 3 with more uniform grain sizes at a lower temperature below typical perovskite phase transition point. With the replacement, PSCs could reach PCE higher than 10%. However, it is still questionable if inorganic CsPbI 3 is formed using "HPbI 3 " which has been questioned by Ke et al. that if it even exists arguing that the product of mixing PbI 2 with hydri odic acid (HI) in N,Ndimethylformamide (DMF) typically used by many research groups is in fact dimethylammonium Inorganic lead halide perovskites have attracted attention due to their tolerance to higher processing temperature and higher bandgap suitable for tandem solar cell application. Not only do they improve cell stability and efficiency, they also reveal many interesting and un-anticipated material qualities. This work reports a simple cation exchange growth (CEG) method for fabricating inorganic high-quality cesium lead iodide (CsPbI 3 ) by adding methylammonium iodide (MAI) additive in the precursor. X-ray diffraction results reveal a multi-stage film formation process whereby i) MAPbI 3 perovskite first formed that acts as a perovskite ...

Experimental Determination of Complex Optical Constants of Air‐Stable Inorganic CsPbI3 Perovskite Thin Films

“…In addition, no any details including the adopted model, fitting parameters, comparison between the ellipsometric data and the fitting results, as well as sample stability were given . Because the PCE of CsPbI 3 perovskite solar cells is progressing fast with latest report of up to 18%, the experimental determination of the optical constants of CsPbI 3 perovskite thin films is never as urgent as now.…”

Structural Evolution During Perovskite Crystal Formation and Degradation: In Situ and Operando X‐Ray Diffraction Studies

“…Despite the non-ideal tolerance factor of all-inorganic halide perovskites, there are successful attempts towards increasing the stability. [32,[81][82][83][84][85][86] One intriguing study revealed the correlation between formation conditions and improved stability: solution deposition on clamped substrates enabled a stable α-CsPbI 3 phase at room temperature. [32] Their in situ GIWAXS analysis of the crystal distortions and strain-driven texture formation showed that the detrimental α-to δ-phase transformation could be suppressed when cooling the thin film to room temperature.…”

Optimizing the Performance of CsPbI3-Based Perovskite Solar Cells via Doping a ZnO Electron Transport Layer Coupled with Interface Engineering

“…For the PSC with a TiO 2 /ZnO bilayer ETL, its PCE is strongly increased to 21.06% by the increased doping concentration in the ZnO layer because of the enlarged FF of approximately 74.07%. These values are far higher than not only those of the PSC with a TiO 2 / ZnO bilayer ETL and low doping concentration and the PSC with a single-layer ZnO ETL and high doping concentration but also those of previous reports [16,28,[60][61][62][63][64][65] as listed in Table 2 and shown in Fig. 8b.…”

“…Hence, the increased doping concentration does not affect the FF and PCE of the PSC with a PCBM/ZnO bilayer ETL. Moreover, although the improved performances of the PSC with a PCBM/ZnO bilayer ETL are superior to those of other CsPbI 3 -based PSCs [16,28,[60][61][62][63][64][65], they are lower than those of the PSC with a TiO 2 /ZnO bilayer ETL, as shown in Fig. 8b.…”