Regulating electronic coupling and molecular vibration to facilitate exciton transfer of fused ring electron acceptors enables 20.66% efficiency of organic solar cells

Abstract

The prerequisite to achieve high‐efficiency organic solar cells (OSCs) is that photon‐generated excitons of organic photovoltaic materials can rapidly diffuse to donor/acceptor interfaces for dissociation before annihilation. However, excitons in organic semiconductors migrate by taking a “hopping” type, leading to a slow transfer rate and thus limited exciton diffusion length, which impedes the further enhancement of power conversion efficiencies in OSCs. Herein, a fused ring electron acceptor, L8‐F, with fluorinated‐phenylalkyl chains is developed and incorporated into L8‐BO to control electronic coupling and molecular vibration of acceptors and efficiently accelerate exciton transfer. L8‐BO:L8‐F blends present weaker exciton–phonon coupling, higher electronic coupling element, smaller recombination energy, and reduced Huang–Rhys factor, due to the enhanced intermolecular interaction and higher crystallinity, compared to L8‐BO. Such enables L8‐BO:L8‐F to acquire a faster exciton transfer rate of 3.4 × 10 ¹⁵  s ⁻¹ and increased exciton lifetime, contributing to prolonged exciton diffusion length of 40.4 nm to benefit exciton dissociation. Furthermore, the higher crystallinity of L8‐BO:L8‐F helps to suppress charge carrier recombination in devices. Therefore, D18:L8‐BO:L8‐F based OSCs acquire impressive power conversion efficiencies of 20.66%, among the highest values for OSCs. This work affords an efficient route to accelerate exciton transfer in OSCs to facilitate exciton dissociation for higher efficiency.

image