Theoretical analysis and the morphology control of vertical phase segregation in high-efficiency polymer/fullerene solar cells

Abstract

The morphology control and optimization in the film-forming process and nanoscale phase separation of donor/acceptor interpenetrating networks played an important role in improving the performance of organic solar cells. Vertical phase separation was defined as an inhomogeneous distribution or concentration gradient of polymer/fullerene blends in the spin-coated film, due to the surface energy of the respective components and their interaction with the substrate or the intermediate buffer layers. In this report, we demonstrated, in detail, the theory of vertical phase separation morphology and control of conventional structure solar cells and inverted configuration solar cells, including the choice of solvents and the drying rate, the surface energy control, thermal annealing, as well as external electric field. In particular, we first proposed internal electronic field model of vertical phase separation and revealed the internal rules and organic semiconductor physics and its mechanism for improving the device efficiency and stability.