Achieving 18.92% efficiency of non-fullerene organic solar cells with active layer morphology optimization by regulating solvent evaporation dynamics

Abstract

Active layer morphology optimization is a widely employed and effective method to enhance the photovoltaic performance of organic solar cells. In this study,D18:L8-BO bulk heterojunction organic solar cells were prepared, and chloroform was utilized as the primary solvent and halogen-free toluene was used as the secondary solvent to optimize the active layer morphology by regulating the solvent evaporation process. Morphological characterization indicates that the optimized volume ratio of chloroform : toluene significantly improves the molecule stacking and domain purity of the donor and acceptor materials, and rational phase separation facilitates exciton dissociation and charge transfer. Electrical property characterization of the transient photovoltage/transient photocurrent, open-circuit voltage and short-circuit current density dependence on light intensity, and the relationship between net photocurrent density and effective voltage indicate that the chloroform : toluene solvent effectively suppresses carrier recombination as well as greatly improves charge transport in the active layer. The proposed strategy provides a practical pathway to improve the power conversion efficiency obviously from 17.89% to 18.92% for the D18:L8-BO organic solar cells. The results highlight the important role of solvent evaporation dynamics in determining the active layer morphology and photovoltaic performance of organic solar cells. Without additives or other complicated processing, the solvent strategy not only contributes to the preparation of more efficient organic photovoltaic devices, but also plays important roles in the large-scale commercialization of organic solar cells.