Advancing PTAA-based perovskite photovoltaics through ionic liquid interfacial engineering

Despite the intrinsic durability of polymeric hole transport materials, poly-triarylamines (PTAA)-based inverted perovskite solar cells (PSCs) have lagged behind their counterparts in efficiency, primarily due to poor surface wettability, insufficient interfacial contact, and unfavorable energy level alignment at the PTAA/perovskite interface. Here, we report a highly effective interfacial engineering strategy employing the ionic liquid 1,3-dimethylimidazolium dimethyl phosphate (DMIMPH) as a multifunctional interfacial modifier. The incorporation of DMIMPH improves PTAA wettability, promoting the growth of high-quality perovskite films with enhanced interfacial contact. Concurrently, DMIMPH effectively tunes the energy levels of PTAA, enhances its electrical conductivity, and passivates interfacial defects with more efficient hole extraction and charge transport. Moreover, its interaction with residual PbI2 modulates perovskite crystallization kinetics, yielding highly crystalline perovskite films with enlarged grain sizes, reduced PbI2 residue, and suppressed trap densities. As a result, PTAA-based p-i-n PSCs employing this approach achieve a record certified power conversion efficiency (PCE) of 24.52%, with a champion efficiency of 25.12%—the highest certified value for PTAA-based perovskite devices to date. Impressively, the DMIMPH-modified PSCs without encapsulation maintained 87.48% of their initial efficiency after 1600 h in air. This strategy offers an effective pathway for advancing the performance and stability of polymer-based inverted PSCs.