Improved efficiency of polymer solar cells using alcohol-soluble self-doped N-type polymers as cathode interface layer

Abstract

Extensive research has been conducted on polymeric cathode interface substances, known for their self-doping features, for their application in organic solar cells (OSCs) to improve the ohmic interaction at the electrode with the active layer. In this paper, two novel polymers, PIIDN-F and PIIDN-FN, with self-doping effect, were successfully synthesized by combining isoindigo (IID), which contains an amino side chain, as an electrons-deficient group with fluorene, which contains different side chains. A thorough examination was conducted on the self-doping properties, electrical conductivity, work efficiency, and the angle of water contact between the two substances. Following this, PIIDN-F and PIIDN-FN were effectively utilized as cathode interface layers (CILs) within PTB7-Th:PC71BM OSCs. The PIIDN-F and PIIDN-FN achieve power conversion efficiencies (PCEs) of 8.97% and 9.04%, respectively. Findings indicate that the quantity of polar groups significantly influences the polymer's conductivity, adjustable work function, and the interaction at interfaces. These results show that by simply adjusting the number of polar groups, it is possible to provide efficient CILs for high-performance OSCs.