Efficient and stable Cs₂AgBiBr₆ double perovskite solar cells through in-situ surface modulation

Lead-free double perovskites have drawn increasing attention for addressing the stability and toxicity challenges from lead-based halide perovskites. However, their power conversion efficiencies (PCE) are still far behind that of Pb-based perovskite solar cells (PSCs) mainly because of the severe energy loss. Herein, we successfully employed the fused-ring electron acceptor (FREA) molecules to passivate defects in Cs₂AgBiBr₆-based double PSCs to realize a dramatically enhanced open-circuit voltage (V_OC) from 1.079 V to 1.278 V and a champion PCE up to 3.31%, which is the highest efficiency for double PSCs to date. The strong binding of C≡N and N=C–S groups on FREA with Ag-exposed surface of Cs₂AgBiBr₆ effectively decreased surface trap densities and considerably suppressed non-radiative recombination. Moreover, the passivated devices showed superior long-term stability, which maintained 98.5% and 97.2% of the initial efficiency under continuous AM 1.5 G illumination and 85 ℃ heating for 300 h, respectively. This work manifests the importance of the rational design of functional passivation molecules to improve the performance and stability of double PSCs.