Control over fibril width via different solubility additives for diketopyrrolopyrrole-based photovoltaic devices

Control over polymeric bulk heterojunction (BHJ) morphology is one of the key factors in obtaining high-efficiency devices. The domain size influence on device performance is widely considered critical. In this paper, the fibril width of 3,6-bis-(thiophen-2-yl)-N,N′-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole and thieno[3,2-b]thiophene (PDBT-TT):[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) blend thin film was adjusted by different processing additives. By decreasing the solubility of PDBT-TT in different additives, the fibril width can be decreased from 65.7 nm to 14.8 nm. It is possible that the PDBT-TT seed-crystallite nuclei concentration is higher in the relatively low solubility solvents than that in the relatively high solubility solvents, thus leading to the formation of narrower fibrils. The PDBT-TT/PC71BM narrow fibrillar interpenetrating network structure was beneficial to exciton separation and charge transport processes. As a result, the solar cell with the narrowest fibril width has a higher short circuit current (J_sc) and fill factor (FF), thus achieving optimized device performance from less than 1% to 4.75%.