Simultaneous Improvement of Efficiency and Stability of Non‐Fullerene‐Based Organic Solar Cells Via Sequential Deposition of Single Donor and Binary Acceptor

Non‐fullerene acceptor (NFA)‐based organic solar cells often exhibit significant cell degradation in power conversion efficiency (PCE) in the early stages of operation, called “burn‐in.” Generally, to fabricate NFA‐based solar cells, binary blend solution deposition (binary BSD) of a conjugated polymer and an NFA is utilized. Herein, the reasons for burn‐in are investigated by aging organic photovoltaic cells with independent control of temperature and light. The results reveal that burn‐in is mainly due to a rapid increase in the interfacial resistance ( R int ) rather than photo‐oxidation of the components or oxidation of the electrode. This R int is effectively suppressed by constructing a ternary photoactive layer through the sequential deposition of a polymer solution and a binary acceptor solution consisting of an NFA and a fullerene acceptor (ternary sequential deposition [ternary SqD]). Under the illumination of 1 sun and thermal annealing at 80 °C for 500 h, the binary BSD exhibits a reduction in efficiency of 63% and 59%, respectively, whereas the ternary SqD demonstrates a reduction of only 32% and 35%, respectively. In addition, the ternary SqD improves the PCE on using fullerene acceptors to enhance light harvesting at short wavelengths.