Rationalizing charge carrier transport in ternary organic solar cells

Abstract

Ternary bulk heterojunction (BHJ) organic solar cells have energy offsets between multiple donors and acceptors. In such bi-continuous percolating films, electron carriers mainly transport in acceptor materials, and hole carriers typically transport in donor materials. Changing the third component of additional donors or acceptors is a common method to fine-tune the transport properties in ternary BHJs. Experimentally, although there are some empirical guidelines for the mobility evaluation, a clear charge transporting model has still not been fully established in multi-component BHJ films. Herein, we observed a general regularity about charge transport that the charge carriers have higher possibilities to transport in polymeric materials even if only low dosage (<10% in weight) polymeric materials are introduced for both the hole and electron cases. From the extended Su–Schrieffer–Heeger model, a polymer “bridge” assisted charge transport mode in small molecules is proposed after the energy offset exceeds the threshold (ΔEe > 0.15 eV). This work provides a perspective for fine tuning the charge transport property in high-performance ternary organic solar cells.