posted on 2020-04-10, 17:11authored byZeng Chen, Xu Chen, Beibei Qiu, Guanqing Zhou, Ziyan Jia, Weijian Tao, Yongfang Li, Yang Michael Yang, Haiming Zhu
Nonfullerene
acceptors (NFAs) have attracted great attention in
high-efficiency organic solar cells (OSCs). While the effect of molecular
properties including structures and energetics on charge transfer
has been extensively investigated, the effect of macroscopic-phase
properties is yet to be revealed. Here we have performed a correlation
study of the nanoscale-phase morphology on the photoexcited hole transfer
(HT) process and photovoltaic performance by combining ultrafast spectroscopy
with high temporal resolution and photo-induced force microscopy (PiFM)
with high spatial and chemical resolution. In PM6/IT-4F, we observe
biphasic HT behavior with a minor ultrafast (<100 fs) interfacial
process and a major diffusion-mediated HT process until ∼100
ps, which depends strongly on phase segregation. Because of the interplay
between charge transfer and transport, a compromised domain size of
20–30 nm for NFAs shows the best performance. This study highlights
the critical role of phase morphology in high-efficiency OSCs.