Lead-Free Bismuth-Based Organic–Inorganic Hybrid Material (2-4py)BiI4 Solar Cell with High Damp-Heat Stability

The high stability and low toxicity of bismuth-based perovskite materials can overcome current issues of lead-based perovskite solar cells (PSCs). In this study, a stable 2-amino-4-picoline (2-4py)-based bismuth perovskite material [(C 6 H 9 N 2 )BiI 4 ] was developed, which has a low band gap and high stability. A one-step solution spin-coating method was used to prepare (C 6 H 9 N 2 )BiI 4 film as the light-absorbing layer. The electron transport layers were composed of compact TiO 2 (c-TiO 2 ) and mesoporous TiO 2 (mes-TiO 2 ). Measurements by UV–vis and time-resolved photoluminescence showed that the band gap of (C 6 H 9 N 2 )BiI 4 film was 2.0 eV and the fluorescence lifetime was 21.58 ns. The materials were assembled into a device, and comparative experimental results showed that the highest power conversion efficiency of fluorine-doped SnO 2 (FTO)/c-TiO 2 + mes-TiO 2 /(C 6 H 9 N 2 )BiI 4 /Spiro-OMeTAD/Au was 0.0328%. Although the efficiency of the current device was low, the (C 6 H 9 N 2 )BiI 4 material exhibited excellent stability in hot and wet conditions. This indicates that (C 6 H 9 N 2 )BiI 4 has potential for use in highly stable solar cells. Graphical Abstract