High Performance As‐Cast Organic Solar Cells Enabled by a Refined Double‐Fibril Network Morphology and Improved Dielectric Constant of Active Layer

Abstract High performance organic solar cells (OSCs) are usually realized by using post‐treatment and/or additive, which can induce the formation of metastable morphology, leading to unfavorable device stability. In terms of the industrial production, the development of high efficiency as‐cast OSCs is crucially important, but it remains a great challenge to obtain appropriate active layer morphology and high power conversion efficiency (PCE). Here, efficient as‐cast OSCs are constructed via introducing a new polymer acceptor PY‐TPT with a high dielectric constant into the D18:L8‐BO blend to form a double‐fibril network morphology. Besides, the incorporation of PY‐TPT enables an enhanced dielectric constant and lower exciton binding energy of active layer. Therefore, efficient exciton dissociation and charge transport are realized in D18:L8‐BO:PY‐TPT‐based device, affording a record‐high PCE of 18.60% and excellent photostability in absence of post‐treatment. Moreover, green solvent‐processed devices, thick‐film (300 nm) devices, and module (16.60 cm 2 ) are fabricated, which show PCEs of 17.45%, 17.54%, and 13.84%, respectively. This work brings new insight into the construction of efficient as‐cast devices, pushing forward the practical application of OSCs.