Due to the hydrophilicity and black-phase instability of FA perovskites, ambient humidity is an unavoidable issue in the processing of perovskite solar cells (PSCs). MACl is among the most popular additives for improving perovskite films, but our experiments confirm that the direct addition of MACl into the precursor solution deteriorates the stability of the final α-FAPbI3 films in humid air, which is attributed to the unwanted pinholes induced by MACl volatilization. To solve this problem, a novel confined-space annealing strategy (CSA) is intentionally developed to control the amount of MACl at a low level. Through retarding the volatilization of MACl and blocking moisture ingress, dense and δ-phase-free FAPbI3 films with excellent crystallinity and stability are achieved at 100 °C under high humidity (RH: 60 ± 10%). We further compare the same amounts of MAI and FACl additives with MACl, discovering that only when MA and Cl work together can pure α-FAPbI3 films be obtained; therefore, a mechanism of MA-assisted nucleation and Cl-induced diffusion recrystallization is inferred. As a result, the PSCs employing optimal films yield a champion power conversion efficiency (PCE) of 17.27% and retain over 90% of the initial PCE after exposure to high humidity for 480 h. Our results offer deep insights into the thermodynamic and kinetic behaviors of MA and Cl in film growth and are beneficial for air-processed FA-based PSCs for commercial application.
Xiaoyan Gan,Kegui Li,Longtao Du,Ruoqi Wang,Yuge Chang,Liling Guo,Hanxing Liu
This study explores the optimization of (TMA)2MA4Pb5I16 perovskite films by regulating the film quality through the addition of MACl and MAAc additives. We found that adding MACl resulted in a film of larger grains with a power conversion efficiency (PCE) of 5.34%, while excessive MACl led to the formation of low-dimensional phases. Adding 7.5% MAAc improved the film quality with a PCE of 5.64%, although excessive MAAc induces pores and smaller grains. To address these issues, we proposed the combined use of MACl and MAAc additives, resulting in films with a larger grain size, smoother surface, and denser structure. Remarkably, the addition of MAAc + MACl achieved a champion PCE of 8.86% with good reproducibility. Mechanism studies revealed that TMA and MAAc formed a stable complex with PbI2 in solution, disrupting nucleation laws and promoting the formation of nuclei, leading to denser films with smaller grains. Additionally, the MACl treatment effectively promoted grain growth, resulting in high-quality films. This study presents novel insights into dual additive usage and their role in film crystallization, offering valuable guidance for the preparation of high-performance perovskite films.
Low bandgap tin–lead halide perovskite (PVSK) presents promising opportunities for high-performance solar cells. However, the randomly crystallized Sn–Pb PVSK with a tin-rich surface is easily oxidized, leading to high-level p-type doping, which hinders the performance enhancement of the solar cell devices. Herein, an efficient anti-solvent passivation strategy to regulate defect, crystallization, and energy conversion performance based on anti-solvents composed of chlorobenzene, isopropanol, and methylammonium chloride (MACl) is proposed. It is shown that the Sn–Pb PVSK film gets more moderate and order, with less PbI 2 and more α-phase PVSK formed. Furthermore, it is revealed that the surface of the as-processed film is Pb-rich, demonstrating a decrease in the surface p-type concentration, which is more suitable for the photoelectric conversion enhancement of the inverting device. Finally, the MACl-assisted post-treated Sn–Pb PVSK invert solar cells exhibit a high current density of 26.49 mA cm −2 with a open-circuit voltage of 0.70 V and a power conversion efficiency of 16.05%. The modified anti-solvent process fuses the advantage of additive and anti-solvent engineering for growing highly crystallized hybrid tin-lead halide PVSK for photovoltaic devices.
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