A series of imide-based small molecules, namely NA, NAA, and NEA with simple structures, were designed and synthesized by introducing different amine side-chains into the benzene unit of imide, which were used as cathode interfacial materials in organic solar cells (OSCs). The amine side-chain substitution positions were systematically investigated with these small-molecule imides. Compared with NA without amide chains-NAA, and NEA, with 3-dimethylaminopropylamine and ethylenediamine chains, respectively-show bathochromic shifts in absorption, decreased band gaps, and higher highest occupied molecular orbital (HOMO) energy levels. A power conversion efficiency (PCE) of 15.04 % was obtained with the NEA-based as-cast OSCs with a high open-circuit voltage and fill factor for PM6 : Y6 blend and the maximum PCE of 15.80 % was reached for as-cast PM6 : Y6 : IT-M ternary OSCs. NEA exhibits better conductivity, higher electron mobility, and stronger the capability of lower work function of cathode among three molecules, affording OSCs with better photovoltaic performance. Additionally, these three molecules show excellent thermal stability both in solution and in films at 150 °C. The results indicate that imide-based small molecules are promising cathode interfacial materials for commercial OSCs.
Keywords: electrode materials; imides; interface engineering; organic solar cells; semiconductors.
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