Title : Conjugated self-assembled monolayers enable redox-stable NiOX interfaces for efficient and durable inverted perovskite solar cells
Abstract:
Nickel oxide (NiOX) is widely employed as a hole transport layer (HTL) in inverted (p–i–n) perovskite solar cells (PSCs) owing to its low cost, high optical transparency, favorable hole mobility, and excellent chemical stability. Nevertheless, the presence of Ni³? species and residual hydroxyl groups on the NiOX surface can trigger undesirable interfacial redox reactions with the perovskite absorber, leading to defect formation and enhanced non-radiative recombination losses. To address these challenges, two conjugated self-assembled monolayer (SAM) molecules, CBT-Ph-CA and CBT-Ph-MN, are introduced as ultrathin interfacial modifiers on the NiOX surface through a facile solution-processing approach. The SAM interlayers effectively passivate surface defects, suppress hydroxyl-induced degradation pathways, and mitigate detrimental interfacial chemical reactions. Furthermore, their strong electronic coupling with NiOX increases the Ni³?/Ni²? ratio and modulates the work function, resulting in improved energy-level alignment and more efficient hole extraction at the NiOX/perovskite interface. The conjugated donor–acceptor molecular framework further promotes charge delocalization and reduces interfacial recombination. Consequently, PSCs incorporating CBT-Ph-CA and CBT-Ph-MN modified NiOx HTLs achieve champion power conversion efficiencies of 23.86% and 24.37%, respectively, significantly outperforming the pristine NiOX-based control device (21.32%). The modified devices also exhibit enhanced open-circuit voltage, fill factor, and operational stability, retaining a higher percentage of their initial efficiency under continuous illumination, thermal stress, and ambient storage conditions. These results demonstrate the effectiveness of CBT-Ph-CA and CBT-Ph-MN as multifunctional interfacial layers for realizing highly efficient and durable inverted perovskite solar cells.
