Naphthalene diimide-based cathode interlayer material enables 20.2%efficiency in organic photovoltaic cells

Cathode interlayer(CIL)materials play an important role in improving the power conversion efficiency(PCE)of organic photovoltaic(OPV)cells.However,the current understanding of the structure-property relationship in CIL materials is limited,and systematic studies in this regard are scarce.Here,two new CIL materials,NDI-PhC4 and NDI-Ph C6 were synthesized by varying the alkylamine chain length on the NDI-Ph core.Our investigation reveals a systematic variation in the physical and chemical properties of these materials with increasing alkylamine chain length.Specifically,we observe a sequential decrease in melting point and self-doping effect,accompanied by an enhancement in crystallinity.Among these CIL materials,NDI-PhC4 has a notable balance across various performance metrics.It also exhibits excellent surface modification capabilities,leading to a low surface roughness.Consequently,OPV cells based on NDI-PhC4 achieve a PCE of 20.2%,which is one of the highest reported efficiencies for OPV cells.In addition,the appropriate melting point of NDI-PhC4 contributes to the excellent stability of OPV cells.