Bismuth Stabilizes the α‑Phase of Formamidinium Lead Iodide Perovskite Single Crystals

• Published in: ACS materials letters Vol. 4; no. 4; pp. 707 - 712
• Main Authors: Kundu, Soumya, Zhang, Dongyang, Askar, Abdelrahman M, Moloney, Erin G, Adachi, Michael M, Nadeem, Ayesha, Moradi, Shahram, Yeddu, Vishal, Abdelhady, Ahmed L, Voznyy, Oleksandr, Saidaminov, Makhsud I
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.04.2022
• ISSN: 2639-4979; 2639-4979
• DOI: 10.1021/acsmaterialslett.1c00778

α-FAPbI3 (FA = formamidinium) perovskite offers an optimal bandgap for single-junction solar cells but converts into a more thermodynamically stable photoinactive δ-polymorph at room temperature. FA- or I-site substitutional alloying stabilizes α-FAPbI3; however, it leads to compositional segregation in operational devices. Here, we stabilize α-FAPbI3 single crystals through Pb-site doping with a heterovalent metal–bismuth (Bi). We show that undoped α-FAPbI3 has an α- to δ-phase half-life transition of <0.15 h, while the optimum concentration of Bi extends it by 4 orders of magnitude. Differential scanning calorimetry (DSC) reveals that Bi has effectively decreased the δ- to α-phase onset transition temperature. Density functional theory (DFT) calculations suggest a relatively clean gap, supporting previous findings on the improved photovoltaic performance of Bi-doped α-FAPbI3-based solar cells.