In-Depth Consideration of Vertically 3D Microstructured Bulk Heterojunction Layers via Solvent Vapor Annealing in DR3TSBDT:PC71BM Solar Cells

Abstract

The physical nature of solvent vapor annealing (SVA) treatment is quite straightforward, and its application is ideal in small molecule-based bulk heterojunction solar cells. It has been suggested to rapidly achieve high-performance small-molecule photovoltaics by alternating the blends to ideally connect the crystallite morphology. However, most previous reports on SVA have shown only influences of the degree of donor/acceptor phase separation within part of active textures. Here, we investigated solution-processed small-molecule solar cells consisting of the previously developed DR3TSBDT and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) after SVA in terms of the vertical gradient crystalline phase in three-dimensional (3D) active layers. These systematic studies of the vertically phase-separated morphology for 3D heterojunction structures clarified in more detail varied active blend morphology underlying SVA and showed a clear structure-property relationship in related device performance. This provided not only a clear understanding of the precise effect of SVA treatments on varied 3D morphological structures but also a path toward the rational optimization of device performance.