Exploring alkylthiol additives in PBDB-T:ITIC blended active layers for solar cell applications

Bulk heterojunction, non-fullerene PBDB-T:ITIC blend polymer solar cells have been fabricated. The active layers consisting of PBDB-T as a donor and ITIC as an acceptor are optimized using a series of alkylthiol additives (1,3-propanedithiol, 1,4-butanedithiol, and 1,8-octanedithiol). It is found that the donor and acceptor are phase separated with different crystalline domains. The additives effectively re-organize the morphology and extend the molecule ordering in lamellar structure with increased correlation length in ITIC domain, benefiting the generation and dissociation of exciton and reducing charge recombination. A substantial improvement in power conversion efficiency of the devices from 8.13% to 9.44% is observed. This study shows that the application of alkylthiol additives is a simple and effective approach to improve the device performance in solar cells based on polymer/non-fullerene blend system.