Thermal-assisted Voc increase in an indenoindene-based non-fullerene solar system

Abstract

An indenoindene-cored small molecule acceptor of 3-ethylrodanine terminals, IBR, was synthesized to achieve high open-circuit voltage (Voc) solar cells. Adopting PBDB-T as the donor and IBR as the acceptor, the as-cast bulk-heterojunction non-fullerene solar cells show a promising Voc of 0.88 V. After a thermal annealing process at 160 °C for 10 min, the PBDB-T:IBR solar cells exhibit an enhanced Voc up to 1.16 V, among the highest Voc value reported for single junction organic solar cells, with obtaining a power conversion efficiency of 6.66%. Detailed investigation indicates that this thermal-activated Voc increase is caused by the microstructural rearrangement within polymer:IBR domains, which diminishes morphological defects, contributes to reduced bimolecular recombination and results in small saturation dark current density of the device. The work demonstrates the potential of IBR as efficient molecular acceptor for high Voc devices of special applications on tandem or ternary solar cells.