Suppression of Interfacial Loss Pathways at Self-Assembled Molecular Hole Transport Layers in Perovskite Solar Cells

The development of stable and efficient perovskite solar cells (PSCs) hinges on the optimization of interfacial energetics and suppression of parasitic loss pathways. While poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl] phosphonic acid (MeO-2PACz) are among the most effective hole transport layers (HTLs) for inverted PSC architectures, each presents trade-offs between operational and reverse-bias stability. This study introduces a strategy to form a composite HTL comprising PTAA and MeO-2PACz that synergistically integrates both materials' advantages while overcoming their limitations. The composite HTL modulates the buried interface to the perovskite, effectively suppressing loss pathways and enhancing the uniformity of the HTL conductivity. Devices incorporating the composite HTL achieve a champion power conversion efficiency (PCE) of 22.83% without additional surface passivation, surpassing the ∼21% achieved by reference devices made using MeO-2PACz or PTAA alone. Moreover, they demonstrate exceptional operational durability and a markedly enhanced reverse bias tolerance. Accompanying drift-diffusion device simulations suggest a previously unexplored loss mechanism at molecular hole transport layers, related to losses induced by electron tunnelling from the perovskite to the hole-collecting contact. Such loss pathways are suppressed when the composite HTL is used, establishing it as a powerful and scalable route toward highly efficient, durable PSCs.