Balancing the Molecular Aggregation and Vertical Phase Separation in the Polymer: Nonfullerene Blend Films Enables 13.09 Efficiency of Organic Solar Cells with Inkjet-Printed Active Layer

摘要

Drop-on demand inkjet-printing (IJP) is a deposition technique with promise in the context of fabricating large-area organic solar cells (OSCs) because of its high material usage, direct-pattern, and large-area roll-to-roll printing compatibility. But its feature of drop-to-drop deposition during IJP makes the film's drying and phase separation process different from spin-coating, and forms different nanophase separation and vertical phase separation morphology. In this work, the nanophase separation of the inkjet-printed organic blend films is systematically studied at different substrate temperatures. The results reveal that increasing the substrate temperature can suppress excess molecules aggregation owing to the high drying speed, leading to improved exciton dissociation efficiency in the blend films. However, the quick drying process at high temperature also leads to a homogenous vertical phase separation, which is not ideal for charge collection. Instead of printing the mixture of donor and acceptor solution directly to form the bulk-heterojunction structure, the polymer donor is printed on the top of the acceptor surface, a so-called layer-by-layer inkjet printing (LBL-IJP) process. By using this LBL-IJP route, balanced nanoscale phase aggregation and gradient vertical phase separation morphology are achieved, which leads to a record power conversion efficiency of 13.09 for the OSCs with an inkjet-printed active layer.