Performance Enhancement in Carbon-Based All-Inorganic Perovskite Solar Cells via a Multifunctional Additive

Carbon-based, hole-transport-layer-free (HTL-free) all-inorganic perovskite solar cells (C-IPSCs) encounter several challenges, including poor crystallization quality, severe surface defects that trigger nonradiative recombination, and phase instability under ambient conditions. These issues limit their efficiency and long-term stability. In this study, we propose a one-step antisolvent method that incorporates guanabenz acetate salt (GBA) as a multifunctional additive to fabricate efficient CsPbI_1.8Br_1.2 C-IPSCs. The C═O and C–O groups in GBA coordinate with uncoordinated Pb²⁺ ions through strong interactions. Simultaneously, the hydrogen bonds between GBA and dimethyl sulfoxide slow down solvent volatilization during annealing, thereby delaying phase transitions. Additionally, the hydrophobic benzene rings in GBA create a protective surface layer that shields the perovskite from moisture ingress, thus preventing the formation of the detrimental photoinactive δ-phase. This multifunctional passivation agent effectively reduces the surface defect state density of CsPbI_1.8Br_1.2 while simultaneously promoting grain enlargement and extending charge carrier lifetimes. Such strategic modifications significantly suppress nonradiative recombination processes, resulting in HTL-free C-IPSCs with enhanced photovoltaic performance. The optimized devices demonstrate a remarkable efficiency increase from 12.03% to 14.34%, coupled with improved long-term stability. This work highlights the synergistic role of GBA in regulating crystallization and passivating defects, thereby presenting a promising strategy for the development of high-performance HTL-free C-IPSCs.