Inverted perovskite solar cells via layer-by-layer deposition of self-assembled monolayers with complementary tail-group steric effects

Self-assembled monolayers (SAMs) have shown great application potential in perovskite solar cells. Among the various SAM molecules, Py3—a fully carbon-based molecule featuring a pyrene tail—has garnered widespread attention owing to its excellent interfacial modulation properties. However, as a bulky polycyclic aromatic hydrocarbon tail group, pyrene occupies a large molecular footprint during self-assembly on NiOx surfaces, inevitably leaving nanoscale voids that create interfacial leakage pathways and induce non-radiative recombination losses. To address this interfacial coverage issue, we propose a layer-by-layer deposition strategy based on the steric complementarity of terminal groups. First, Py3 molecules with rigid pyrene terminal groups are deposited on the NiOx surface to form an initial interface with specific steric and coverage characteristics. Subsequently, MeO-2PACz is introduced to further modify the insufficiently covered regions. The two molecules possess distinct terminal-group structures and interfacial assembly characteristics, allowing layer-by-layer deposition to improve the completeness and compactness of molecular coverage at the interface. Experimental results demonstrate that the optimized layer-by-layer deposited device achieves simultaneous enhancements in fill factor and open-circuit voltage, with the power conversion efficiency increasing from 22.28% to 23.36%. This work provides a new strategy for precisely regulating carrier transport at semiconductor interfaces through molecular tail engineering.