Thermal and Photo‐Degradation Study of α‐FAPbI₃‐Based Perovskite Using In Situ X‐Ray Diffraction

Abstract

Hybrid halide perovskite has established its credibility as high performance thin film photovoltaic technology. Perovskite based on formamidinium cation is at the core composition to top performances and stability. Herein, a depth study based on temperature‐controlled in situ X‐ray diffraction focusing on the photo‐active formamidinium lead iodide (α‐FAPbI3) is reported. In particular, the thermal stability of the latter and the degradation pathways under different experimental conditions are clarified. Based on this in situ technique, the lattice thermal expansion coefficient is reported that provides relevant information on possible mechanical stress created upon temperature cycling or damp heat test. The results support that α‐FAPbI3 degradation is substantially accelerated when temperature is combined to illumination and when it is interfaced with the extraction layers. In addition, by contrast to in darkness for which α‐FAPbI3 degrades directly into PbI2, the existence of a temperature gap under illumination involving an intermediate step with a non‐crystalline phase resulting from the perovskite degradation and contributing to the formation of PbI2 by‐product is revealed.

Spectral Splitting Solar Cells Consisting of a Mesoscopic Wide-Bandgap Perovskite Solar Cell and an Inverted Narrow-Bandgap Perovskite Solar Cell

“…A wide-bandgap Pb perovskite of composition FA 0.85 MA 0.15 Pb­(I 0.85 Br 0.15 ) 3 doped with the 5% potassium ion was fabricated for the top cell. FAPbI 3 has been applied to high-efficiency PSCs due to its superior characteristics such as an optimal bandgap, a longer diffusion length, and a high thermal stability. , Furthermore, the addition of MABr to FAPbI 3 is effective to suppress the transformation of α-phase to δ-phase at room temperature, which is unfavorable for efficient PSCs. − The reason why the 5% potassium ion was doped into FA 0.85 MA 0.15 Pb­(I 0.85 Br 0.15 ) 3 is the reduction of the hysteresis of PSC, according to the previous report from Tang et al A Sn–Pb perovskite of composition Cs 0.025 FA 0.475 MA 0.5 Sn 0.5 Pb 0.5 I 3 with a narrow bandgap that works with a high PCE was chosen for the bottom cell . The detailed fabrication process of each perovskite film is given in the Experimental Methods, and the top-view scanning electron micrographs of the perovskite films are shown in Figure S1.…”

Single-Crystal Methylammonium-Free Perovskite Solar Cells with Efficiencies Exceeding 24% and High Thermal Stability

“…Prior studies have shown that MAPbI 3 has a low decomposition temperature (∼60 °C) . Thus, prolonged exposure to thermal stress will likely lead to the gradual decomposition of the MA components in FA 0.6 MA 0.4 PbI 3 . In addition, it was observed that unencapsulated SC-PSCs exhibit a tendency to delaminate from extended exposure to thermal stress at 85 °C .…”