Modulation of donor-acceptor interface through thermal treatment for efficient bilayer organic solar cells

In this article, we demonstrate the effect of donor-acceptor (D-A) interface on the performance of bilayer organic solar cells. Solution processing was used to develop liquid crystal poly(9, 9′-dioctylfluorene- cobithiophene) (F8T2) polymer films and variable morphology of the films was achieved by varying the annealing temperature. The morphology of the annealed active layers signature a well-aligned nanodomain feature with an interdegitated structure at 200 °C. The devices with bilayer configuration, ITO/PEDOT:PSS/F8T2/C₇₀/Al, have yielded a power conversion efficiency (PCE) of 3.4(±0.2)% under 1 sun incident radiation. We attribute the high PCE to the increased D-A junction interface and balanced charge transport between electron/hole transport layers.