High-Performance Ternary Organic Solar Cells with Controllable Morphology via Sequential Layer-by-Layer Deposition.

Ternary blending of light-harvesting materials has been proven to be a potential strategy to improve the efficiency of solution-processed organic solar cells (OSCs). However, the optimization of a ternary system is usually more complicated than that of a binary one as the morphology of conventional ternary blend films is very difficult to control, thus undermining the potential of ternary OSCs. Herein, we report a general strategy for better control of the morphology of ternary blend films composed of a polymer donor and two nonfullerene small-molecule acceptors for high-performance OSCs using the sequential layer-by-layer (LbL) deposition method. The resulting LbL films form a bicontinuous interpenetrating network structure with high crystallinity of both the donor and acceptor materials, showing efficient charge generation, transport, and collection properties. In addition, the power conversion efficiencies (PCEs) of the ternary LbL OSCs are less sensitive to the blending ratio of the third component acceptor, providing more room to optimize the device performance. As a result, optimal PCEs of over 11, 13, and 16% were achieved for the LbL OSCs composed of PffBT4T-2OD/IEICO-4F:FBR, PBDB-T-SF/IT-4F:FBR, and PM6/Y6:FBR, respectively. Our work provides useful and general guidelines for the development of more efficient ternary OSCs with better controlled morphology.