Subtly adjusted active layer self‐assembly process for efficient organic solar cells

The phase separation degree of active layers plays a vital role in enhancing the power conversion efficiency of organic solar cells. Two post treatments were employed to optimize the phase separation degree of active layers by subtly adjusting the self‐assembly process for SMPV1:PC₇₁BM based active layers (SMPV1, 2,6‐bis2,5‐bis(3‐octylrhodanine)‐(3,3‐dioctyl‐2,2':5,2''‐terthiophene)]‐4,8‐bis((5‐ethylhexyl)thiophen‐2‐yl)benzo1,2‐b:4,5‐b']dithiophene; PC₇₁BM, 6,6]‐phenyl‐C₇₁‐butyric acid methyl ester). In this work, a power conversion efficiency of 7.93% was obtained for devices with an as‐cast active layer, which is close to the highest values reported for SMPV1 based devices. The power conversion efficiency was further increased to 8.64% or 8.99% for active layers with thermal annealing or thermal annealing together with solvent vapor annealing, respectively. The enhanced performance is mainly attributed to more efficient photon harvesting and charge transport induced by the post annealing treatment of the active layers. The face‐on molecular orientation of SMPV1 is increased for active layers with post annealing treatment, which is beneficial for charge transport along directions perpendicular to the substrate. This work further confirms the positive effect of post annealing treatment on the performance improvement of organic solar cells. © 2019 Society of Chemical Industry