Strong self-trapping by deformation potential limits photovoltaic performance in bismuth double perovskite

• Main Authors: Wu, Bo, Ning, Weihua, Xu, Qiang, Manjappa, Manukumara, Feng, Minjun, Ye, Senyun, Fu, Jianhui, Lie, Stener, Yin, Tingting, Wang, Feng, Goh, Teck Wee, Harikesh, Padinhare Cholakkal, Tay, Eugene Yong Kang, Shen, Zexiang, Huang, Fuqiang, Singh, Ranjan, Zhou, Guofu, Gao, Feng, Sum, Tze Chien
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2021
• Subjects: Science::Physics; Perovskite; Bismuth
• Online Access: https://hdl.handle.net/10356/151013
• Institution: Nanyang Technological University

Bismuth-based double perovskite Cs2AgBiBr6 is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.5 ± 0.1 × 10−11 cm3 s−1) and low charge carrier mobility (around 0.05 cm2 s−1 V−1). Besides intermediate Fröhlich couplings present in both Pb-based perovskites and Cs2AgBiBr6, we uncover evidence of strong deformation potential by acoustic phonons in the latter through transient reflection, time-resolved terahertz measurements, and density functional theory calculations. The Fröhlich and deformation potentials synergistically lead to ultrafast self-trapping of free carriers forming polarons highly localized on a few units of the lattice within a few picoseconds, which also breaks down the electronic band picture, leading to efficient radiative recombination. The strong self-trapping in Cs2AgBiBr6 could impose intrinsic limitations for its application in photovoltaics.