Self-doping n-type polymer as cathode interface layer enables efficient organic solar cells

Polymer cathode interface materials with self-doped properties have been extensively researched for application in organic solar cells (OSCs) to strengthen the ohmic contact between the photoactive layer and the electrode. Here, three new n-type polymeric interfacial materials were designed and synthesized with self-doping effects. The self-doping behavior, water contact angle, conductivity, work function of three materials were systematically investigated. Subsequently, these three novel n-type materials were successfully applied as cathode interface layers (CILs) in PTB7-Th:PC71BM-based OSCs and could achieve a remarkable power conversion efficiency of 9.01%. It was found that the number and position of polar groups have a strong influence on the electrical conductivity, tunable work function and interfacial interactions of these polymers. These results suggest that simple adjustment of the position and number of polar groups can provide an effective method for developing efficient CILs for high-performance OSCs. [Display omitted] •Three new naphthalenediimines based cathode interfacial materials were synthesized.•PNDI-FN, PNDI-N-F and PNDI-N-FN have different numbers and positions of polar groups.•Modulating the position and number of polar groups enhanced the device performance.•Achieved high PCE of 8.27%, 8.48% and 9.01% for PNDI-FN, PNDI-N-F and PNDI-N-FN, respectively.