2,4,6-trimethylphenyl)amine] (PTAA) [7] as the hole transport material (HTM). However, there is still a gap of more than 5% between the record efficiency and the maximum efficiency of thermally stable PSCs. So far, the thermal stability of perovskite absorber materials has been improved by engineering perovskite composition; both cation [8][9][10][11] and halide [10][11][12][13] composition engineering have been conducted. Also, 2D-3D incorporated perovskite materials for high thermal stability have been recently suggested. [14][15][16] On the other hand, multication approach is one of the promising ways to achieve highly efficient PSCs. [7,17] However, at the same time, it is more and more difficult to understand and control such a large number of components for highly efficient and highly stable PSCs. In case of our previous study for quadruple cation PSCs, [7] seven components of formamidinium (FA), methylammonium (MA), Cs, Rb, Pb, I, and Br should be controlled. Furthermore, not only effect of single element but also combination effect of these elements should be important. Thus, careful studies are required for further development. Indeed, even though more and more studies have been reported on multication approach, [18][19][20][21] there are still no reports of PSCs that meets international standard (IEC 61215); 85 °C/85% relative humidity (RH) stress test with high efficiency. Here we focus on the dependence of device thermal stability on perovskite composition by using state-of-the-art highly efficient PSCs (≈20%) to achieve compatibility of high efficiency and high thermal stability.We tested the thermal stability of devices with a structure of indium tin oxide (ITO)/compact titanium dioxide (TiO 2 )/ mesoporous TiO 2 /perovskite/PTAA/gold (Au). The starting perovskite composition used here was Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb (I 0.83 Br 0.17 ) 3 because this composition has been reported to display high efficiency and high operational stability. [17] We chose PTAA as the HTM because its high efficiency [22][23][24] and high thermal stability [7] have been reported respectively. In addition, we used a low doping concentration of 3 mol% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in PTAA in this experiment to minimize any adverse effects of the additives on the device thermal stability reported so far. [25][26][27] First, we examined the relationship between efficiency and thermal stability for devices with different PbI 2 ratios in the Perovskite solar cells have received great attention because of their rapid progress in efficiency, with a present certified highest efficiency of 23.3%. Achieving both high efficiency and high thermal stability is one of the biggest challenges currently limiting perovskite solar cells because devices displaying stability at high temperature frequently suffer from a marked decrease of efficiency. In this report, the relationship between perovskite composition and device thermal stability is examined. It is revealed that Rb can suppress the growth of PbI 2 even un...

Organic−inorganic lead halide perovskites are promising materials for realization of low-cost and high-efficiency solar cells. Because of the toxicity of lead, Sn-based perovskite materials have been developed as alternatives to enable fabrication of Pb-free perovskite solar cells. However, the solar cell performance of Sn-based perovskite solar cells (Sn-PSCs) remains poor because of their large open-circuit voltage (V OC ) loss. Sn-based perovskite materials have lower electron affinities than Pb-based perovskite materials, which result in larger conduction band offset (CBO) values at the interface between the Snbased perovskite and a conventional electron transport layer (ETL) material such as TiO 2 . Herein, the relationship between the V OC and the CBO in these devices was studied to improve the solar cell performances of Sn-PSCs. It was found that the band offset at the ETL/ perovskite layer interface affects the V OC of the Sn-PSCs significantly but does not affect that of the Pb-PSCs because the Sn-based perovskite material is a p-type semiconductor, unlike the Pb-based perovskite. It was also found that Nb 2 O 5 has the CBO that is closest to zero for Sn-based perovskite materials, and the V OC values of Sn-PSCs that use Nb 2 O 5 as their ETL are higher than those of Sn-PSCs using TiO 2 or SnO 2 ETLs. This study indicates that control of the energy alignment at the ETL/perovskite layer interface is an important factor in improving the V OC values of Sn-PSCs.

The performances of ZnSnP2, CdSnP2, and Zn1-xCdxSnP2 alloys as solar cell photoabsorbers are assessed using photovoltaic conversion efficiency simulations in conjunction with first-principles calculations based on hybrid density functional theory. The band gap of Zn1-xCdxSnP2 decreases with increasing Cd content x and shows a small bowing. The electronic structure and optical absorption spectrum depend weakly on the composition, aside from the band gap and spectral threshold. The conversion efficiency is almost converged to the Shockley–Queisser limit at a photoabsorber thickness of a few micrometers for any composition of Zn1-xCdxSnP2, similarly to the cases of GaAs, CdTe, CuInSe2, and CuGaSe2.

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Recently, organic-inorganic halide perovskites have received attention for applications in solar cells. Measurements of high-quality single crystals reveal lower defect densities and longer carrier lifetimes than those of conventional thin films, which result in improved electrical and optical properties. However, single crystal surfaces are sensitive to exposure to ambient conditions, and degrade under long-term storage in air. The surface also shows differences from the bulk in terms of its optical and electronic characteristics. For a heterojunction device, the interface at the single crystal is important. Understanding the difference between the surface and bulk properties offers insights into device design. Here, we prepared non-sliced and sliced formamidinium lead iodide (FAPbI; FA = HC(NH)) single crystals with a bandgap of 1.4 eV, which matches well with the requirements for solar cell photoabsorption layers. We evaluate the energy level diagrams of the surface and bulk regions, respectively. Our data indicate that the valence band maximum of the surface region is at a higher energy level than that of the bulk region. We also discuss hypotheses for the well-known and unexplained phenomena (multiple bandgaps and bandgap narrowing) seen in the absorption and photoluminescence spectra of single crystals. We conclude that these effects are likely caused by a combination of the degraded surface, Rashba-splitting in bulk, and self-absorption by the single crystal itself.