Rationalization of the selectivity in the optimization of processing conditions for high-performance polymer solar cells based on the polymer self-assembly ability

Tailoring the blend morphology in a bulk heterojunction device is of critical importance but remains a challenge today. Although the morphologies of polymer solar cells can be tuned by thermal/solvent annealing or by incorporation of solvent additives, optimizing the morphology of the active layer for a newly synthesized polymer has, to date, remained mostly an empirical approach. In this work, three typical polymers in organic photovoltaics have been studied. By processing at different conditions, each polymer reveals high selectivity in the optimizing methods. Optical spectrum and electrostatic force microscopy results demonstrate morphology as the main reason for various device performances. Further, these can be traced back to the self-assembly behaviors of polymers. By the established relationships between molecular structure, morphology, and the corresponding device performances, we propose a self-assembly based process-selection guideline for efficient performance improvement of newly synthesized materials.