Improving the Thermal Stability of Organic Solar Cells via Crystallinity Control

The past decade has witnessed the prosperity of organic photovoltaic cells (OPVs). In addition to efficiency and cost, stability is another challenge that OPVs face in their practical application. Continuous thermal stress often accelerates the crystallization and phase separation of active layers, leading to a decreased photovoltaic performance. Developing simple and effective strategies to prolong the lifetime of OPVs under heating has attracted increasing attention. In this work, an unexplored random copolymer named PY was incorporated as a high-temperature-resistant aid to the emerging nonfullerene OPVs to control and stabilize the film morphology. Using the well-known low-cost P3HT:O-IDTBR as the model photoactive layer, OPVs with small weight amounts (less than 30%) of PY achieved comparable photovoltaic efficiencies. Notably, the 10%-ternary blend maintained over 70% of its initial efficiency after annealing at 150 °C for 8 days, while the efficiency of the binary system dropped rapidly. Notably, this approach was also effective for the high-efficiency PM6:BTP-eC9 blend. Combined with the morphology and crystallization characterization techniques, the relationship between microstructure and thermal stability was constructed. This work thus demonstrated an effective and broadly applicable strategy to improve the thermal stability of OPVs without sacrificing the initial efficiency.