Improving the efficiencies of small molecule solar cells by solvent vapor annealing to enhance J-aggregation

Abstract

We report highly efficient small molecule organic solar cells (SM-OSCs) based on a porphyrin derivative electron donor of ZnP2-DPP and an electron acceptor of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) by using a solvent vapor annealing (SVA) method with a series of low boiling solvents. Absorption spectral studies indicate that carbon disulfide (CS₂) SVA induces J-aggregation in blend films accompanied by expanded and enhanced absorption which contributes largely to the fabrication of broader light response and larger short-circuit current (J_SC) solar cell devices. In addition, we systematically analyze the relationship between the film morphology and device performance. Finally, the electronic study shows that the CS₂ SVA-treated device showed a higher exciton generation rate and enhanced carrier collection efficiency. And the morphology study indicates that the blend films treated with CS₂ SVA exhibit tighter molecular packing, better crystallization and an appropriate phase separation length scale. In other words, these collective electronic and morphological features correlate well with the champion J_SC, the fill factor (FF) and the power conversion efficiency (PCE) of the CS₂ treated devices.