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.