Bidirectional functionality of a modified PCBM layer : enhancing perovskite photovoltaics beyond single-bandgap devices

Abstract

Metal electrode corrosion driven by halide migration and interfacial defects remains a significant bottleneck limiting the operational stability and photovoltaic performance of perovskite solar cells (PSCs), particularly in devices with varied bandgaps. Herein, we present a multifunctional interface engineering strategy by incorporating the IL 1-butylpyridinium tetrafluoroborate (BPYBF4) into the PCBM electron transport layer to simultaneously address these issues. The BF4− anions coordinate with the Ag+, forming a corrosion-resistant layer that mitigates iodine-induced degradation. Concurrently, the BPY+ cations react with residual PbI2 at the perovskite surface, inducing the formation of a 1D perovskite capping layer that effectively passivates interfacial defects and suppresses ion migration. Phase-transition process during film conversion was systematically investigated, revealing a gradual transformation of residual PbI2 into a protective 1D perovskite structure upon BPYBF4 incorporation. Additionally, the presence of ionized PCBM enhances surface potential alignment, promoting efficient electron extraction and reducing non-radiative recombination losses. This strategy demonstrates broad applicability—not only enhancing the performance of 1.55 eV normal-bandgap PSCs but also achieving outstanding efficiency for wide-bandgap PSCs, with PCEs of 22.69% for 1.67 eV and 18.60% (certified at 17.75%) for 1.85 eV, respectively. This work provides a facile and scalable approach to simultaneously protect the electrode and stabilize the perovskite films, offering a promising strategy for varied bandgaps PSCs in both single-junction and tandem configurations.