Balanced Distribution of Donor and Acceptor Enabled by Volatile Isomerization Additives for 20.81% Efficiency Layer-by-Layer Polymer Solar Cells

Abstract

The controlled interdiffusion and balanced distribution of donor and acceptor are the key to regulating the vertical phase separation morphology and achieving high-performance layer-by-layer polymer solar cells (LBL PSCs). In this work, two volatile isomerization additives 2-bromo-5-iodo-1,3-dimethylbenzene (2-BrIDB) and 5-bromo-2-iodo-1,3-dimethylbenzene (5-BrIDB) were developed to finely regulate the interdiffusion between D18 and L8-BO, enabling more balanced distribution of donor and acceptor, and improved vertical phase separation morphology. Two isomerization additives can effectively enhance the molecular ordered stacking of L8-BO and regulate the interdiffusion between D18 and L8-BO, especially the liquid additive 2-BrIDB, which exhibited stronger non-covalent interaction with L8-BO and partial dissolution of D18 films, prolonging the film-forming time, facilitating effective swelling of D18 and promoting intimate interdiffusion between D18 and L8-BO. As a result, the additive-treated films achieved the optimal vertical phase separation morphology with more balanced distribution of D18 and L8-BO and more ideal D/A interpenetrating bicontinuous network structure, providing higher power conversion efficiency (PCE) of 20.81% and 19.43% for 2-BrIDB and 5-BrIDB, respectively. Our work provided insights into achieving excellent vertical phase separation morphology and high-performance LBL PSCs by regulating the interdiffusion between donor and acceptor to balance the distribution through the use of volatile isomerization additives.