20.0% efficiency of ternary organic solar cells enabled by a novel wide band gap polymer guest donor

The ternary strategy has emerged as a promising approach to further improve the device performance of organic solar cells (OSCs). Herein, a novel wide bandgap polymer donor P(BTzE-BDT) was synthesized and incorporated into the PM6:BTP-eC9 system to fabricate ternary OSCs. P(BTzE-BDT) exhibits complementary absorption spectra and excellent compatibility with PM6, facilitating the fine-tuning of photon harvesting and the morphology of the ternary blend films. This leads to a simultaneous increase in the short-circuit current density (JSC) and fill factor (FF). By promoting intensive molecular packing and reducing domain size, P(BTzE-BDT) optimizes the morphology, contributing to improved and well-balanced charge transport, suppressed carrier recombination, and efficient exciton dissociation. Consequently, ternary OSCs with a 5% addition of P(BTzE-BDT) exhibit a higher power conversion efficiency (PCE) of 20.0%, compared to 18.8% for the binary system. Furthermore, thick-film devices were fabricated to assess their commercialization potential, achieving a PCE of 18.2% with an active layer thickness of 300 nm, compared to 16.3% for the binary device. This comprehensive study underscores the potential of P(BTzE-BDT) as a promising guest molecule for optimizing morphology, which is crucial for achieving high efficiency in OSCs, thereby paving the way for practical commercial applications.