Aggregation Regulation of Acceptor via Thiophene‐Substituted Alkyl Chains Enables High‐Performance Toluene‐Processed Organic Solar Cells without Additive and Post‐Treatment

Abstract Due to the mismatched aggregation behavior and limited compatibility between the donor and acceptor, it is a challenge for the active layer of organic solar cells (OSCs) to spontaneously realize well‐developed morphology in nonhalogenated solvents. In this contribution, an aggregation regulation strategy for acceptors with strong aggregation is developed via thiophene‐substituted alkyl chain engineering to fabricate high‐performance nonhalogenated solvent‐processed OSCs without an additive or post‐treatment. With the replacement of alkyl chains with steric conjugated thiophene‐substituted alkyl chains, the resulting acceptor (namely BTP‐2T , BTP‐T , and BTP‐T‐BO ) shows reduced aggregation to match the polymer donor D18‐Cl using toluene as a processing solvent, enabling ordered molecular arrangement and uniform phase separation morphology. Especially, the combined modification of the asymmetric thiophene‐substituted inner chain and branched outer side chains for BTP‐T‐BO enables the formation of a superior nanoscale bi‐continuous interpenetrating network along with ordered and compact molecular packing in the D18‐Cl: BTP‐T‐BO blend. As a result, an excellent PCE of 18.05% is achieved in the D18‐Cl: BTP‐T‐BO ‐based device using toluene as the processing solvent without any extra treatment, which is the highest value for nonhalogenated solvent‐processed OSCs without any extra treatment.