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 a combined strategy of conjugated core extension and 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 improved planarity, which promotes intrinsic crystallinity and leads to a significantly stronger self-doping effect. Moreover, this optimized configuration enables NDIT2 to exhibit highly ordered molecular assembly, which 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 NDI1 along 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 synergistic modulation of molecular conjugation and configuration.