Enabling over 20% Efficiency Organic Solar Cells by Molecular Configuration Modulation of Naphthalene Diimide-based Cathode Interlayers

Cathode interlayers (CILs) are pivotal to achieving high power conversion efficiency (PCE) in organic solar cells (OSCs). Herein, three D-A type CILs (NDIT1, NDI1, NDIT2) with different bridging structures were designed and synthesized through molecular configuration regulation. We then conducted a systematic investigation to unravel the influence of these distinct molecular structures on OSCs performance. In this series, the rigid fused ring bridge in NDIT2 endows a significantly improved planar molecular skeleton, which not only promotes enhanced intrinsic crystallinity but also leads to a significantly stronger self-doping effect. Moreover, this optimized configuration enables NDIT2 to exhibit highly ordered molecular assembly, which directly facilitates the formation of a uniform, low-defect nanostructure at the interface with the photoactive layer, which facilitates charge transport and extraction efficiency while effectively suppressing charge recombination losses. As a result, OSCs based on NDIT2 deliver a champion PCE of 20.03%, exceeding the efficiency of 18.95% for devices based on NDIT1 and 19.16% for devices based on NDI1along with excellent initial operational stability. This study provides an effective and rational strategy for designing high-performance cathodes by precisely optimizing the performance of CILs through targeted molecular structure regulation.