Remove the Residual Additives toward Enhanced Efficiency with Higher Reproducibility in Polymer Solar Cells

Undesirable efficiency reproducibility was sometimes observed in fabrication of high performance polymer solar cell devices incorporating high boiling point additives. The anomalous results originated from the slow drying of additives not only reduced the controllability of device performance but also impeded the studies of device physics and material design. How to remove the residual additives and achieve stable interface properties is crucial for both the academic and industrial community. Herein, we demonstrated that the morphological stability is enhanced and efficiency reproducibility is increased obviously from 7.07 +/- 0.27% to 7.53 +/- 0.12% after spin-coating inert solvents for the PBDTTT-C-T/PCBM system. The relationship between processing conditions and photovoltaic performance was well explored and demonstrated via multiple techniques including atomic force microscopy, Kelvin probe force microscopy, transmission electron microscopy, and X-ray photospectroscopy. Most importantly, this method was successfully employed in more than five representative donor polymers. Our study suggested that the slow drying process of the residual high boiling point additives could induce undesirable morphological variation as well as unfavorable interfacial contact, and by washing with low boiling point "inert" solvent, like methanol, the negative influence caused by the residual additive can be avoided and hence the additives would perform more efficiently in the optimization of device performance of highly efficient PSCs.