Achieving 19.6% efficiency in organic photovoltaics through guest-polymer assisted morphological fibrillization†

Achieving high-performance organic photovoltaics (OPVs) hinges on optimizing the phase separation and interfaces within the active layer, which is crucial for efficient charge generation and transport. While a fibril-like phase-separated network has been widely recognized as the desirable morphology across various blend systems, robust methods to consistently achieve this structure remain elusive, limiting further efficiency gains. Here, we introduce a morphological control strategy using an imide-functionalized benzotriazole polymer, PTzBI-dF, within a D18:L8-BO blend to enhance fibrillar morphology. PTzBI-dF exhibits preferential miscibility with D18, fostering π–π stacking and increasing crystallinity, which result in a well-defined fibrillar network that optimizes its electrical and photophysical properties. Therefore, the D18:PTzBI-dF:L8-BO device achieves a remarkable power conversion efficiency of 19.6% for 0.04 cm² devices and a certified 18.35% for 1 cm² devices, representing the highest value reported so far for 1 cm² devices. Furthermore, this guest-polymer-assisted fibrillization shows versatility across various blend systems, offering a promising approach for enhancing OPV performance.