Vapor-assisted deposition of highly efficient, stable black-phase FAPbI(3) perovskite solar cells

HZ Lu and YH Liu and P Ahlawat and A Mishra and WR Tress and FT Eickemeyer and YG Yang and F Fu and ZW Wang and CE Avalos and BI Carlsen and A Agarwalla and X Zhang and XG Li and YQ Zhan and SM Zakeeruddin and L Emsley and U Rothlisberger and LR Zheng and A Hagfeldt and M Gratzel, SCIENCE, 370, 74-+ (2020).

DOI: 10.1126/science.abb8985

Mixtures of cations or halides with FAPbI(3) (where FA is formamidinium) lead to high efficiency in perovskite solar cells (PSCs) but also to blue-shifted absorption and long-term stability issues caused by loss of volatile methylammonium (MA) and phase segregation. We report a deposition method using MA thiocyanate (MASCN) or FASCN vapor treatment to convert yellow delta-FAPbI(3) perovskite films to the desired pure alpha-phase. NMR quantifies MA incorporation into the framework. Molecular dynamics simulations show that SCN- anions promote the formation and stabilization of alpha-FAPbI(3) below the thermodynamic phase-transition temperature. We used these low-defect-density alpha- FAPbI(3) films to make PSCs with >23% power-conversion efficiency and long-term operational and thermal stability, as well as a low (330 millivolts) open-circuit voltage loss and a low (0.75 volt) turn-on voltage of electroluminescence.

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