High‐Efficiency Thick Film Binary Organic Photovoltaics via Asymmetric Alkyl Chain Engineering

Abstract The development of high‐performance organic photovoltaics (OPVs) with thick film active layers is key to moving this technology from laboratory preparation to industrial production. Design and synthesis of active layer materials to achieve a bi‐continuous interpenetrating morphology with appropriate nanoscale phase separation has been demonstrated as an effective method to realize high‐efficiency thick film devices. Here, two non‐fullerene acceptors are developed to compare the effect of symmetric (diDT‐BO) and asymmetric (DTC11‐BO) substituted alkyl chains on active layer morphology and device performance by introducing asymmetric side chains to the central core pyrrole ring. Based on the solubility and crystallinity differences of DTC11‐BO and diDT‐BO, the power conversion efficiencies (PCEs) of 19.0% and 18.1% are realized with D18 as the donor. Importantly, D18:DTC11‐BO devices with 300 and 500 nm active layers achieve excellent PCEs of 17.7% and 16.1%, which are among the top‐class values for thick film OPVs reported to date. The work demonstrates that tunning the crystallinity by optimizing the asymmetric alkyl chains is an effective material design strategy to achieve high‐efficiency thick film OPVs.