Bathocuproine interfacial layer leads to solid improvement of reproducibility and stability of Pb-free CsBi 3 I 10 based perovskite solar cells

Bismuth-based perovskite solar cells (Bi-PSCs) have gained considerable interest due to their excellent optoelectronic properties but suffer from low performance in terms of reproducibility and stability. The existence of crystal defects in the Bi-perovskite film and interfacial defects at the Bi-perovskite/electron transport layer (ETL) has been understood to be responsible for the limited performance of the respective PSCs. In this research, we focused on these two issues to improve the reproducibility of the Bi-PSCs. First, we have optimized the fabrication conditions for CsBi 3 I 10 (CBI) perovskite with reduced crystal defects. CBI films fabricated with a solution concentration of 1.0 M and post-annealed at 120 °C show high crystallinity with a bandgap of 1.78 eV and a carrier lifetime of 1.92 ns. Second, for the first time in Bi-PSCs, we introduced an ultrathin (6 nm) bathocuproine (BCP) interfacial layer (BIL) at the CBI/ETL interface for inverted planar PSCs. The inclusion of BIL as a hole leakage blocker in the perovskite/ETL interface improved electrical interface contact and significantly enhanced the PSC performance. This interfacial engineering by BIL improved power conversion efficiency (PCE) of 0.80% with high reproducibility, which was significantly higher than control PSCs (0.38%). Moreover, PSCs with BIL retained ~ 90% of their initial efficiency even after 528 h because of the lower charge accumulation within the respective PSC. This study demonstrates the importance of including a BIL at the CBI/ETL interface for fabricating stable and reproducible Bi-based PSCs.