High-Efficiency Thermal-Annealing-Free Organic Solar Cells Based on an Asymmetric Acceptor with Improved Thermal and Air Stability

The stability of organic solar cells (OSCs) is an urgent problem for commercialization. In this work, a novel asymmetric molecule TB-4Cl was designed and synthesized. Quantum chemical computations revealed that TB-4Cl has a larger dipole moment of 1.98 Debye than that of Y6, which can induce a stronger intermolecular interaction. Without thermal annealing, devices based on PM6:TB-4Cl achieved a higher efficiency of 14.67%. Impressively, all of the devices showed a negligible difference in power conversion efficiency (PCE) before and after thermal-annealing treatment. Compared to the unencapsulated PM6:Y6-based devices, PM6:TB-4Cl-based devices exhibited improved thermal and air stability, evidenced by retaining around 75% (TB-4Cl) and 60% (Y6) after being heated at 100 °C in nitrogen for 110 h and 65% (TB-4Cl) and 50% (Y6) in air for 92 h. This work indicates that an A-D1A'D2-A asymmetric molecule can be a promising candidate for achieving stable OSCs with high efficiency.