Simple transfer from spin coating to blade coating through processing aggregated solutions†
To develop an understanding of the effect spin coating or blade coating have on the morphology of polymer:fullerene thin films for organic solar cells, we have investigated the morphology of poly[5-(2-hexyldecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophene-2-yl)-thiophene)] (P(T3-TPD)) blended with phenyl-C71-butyric acid methyl ester (PC71BM) using the solvent additive 1,8-diiodooctane (DIO). When P(T3-TPD) : PC71BM mixtures are cast with DIO, we observed a fivefold increase in power conversion efficiency (PCE) from 1% to >5% for both spin and blade coated devices. We found the morphology and OPV performance are remarkably similar for spin and blade coated films without having to re-optimize the processing solution or coating temperature. We attribute the robust coating behavior to processing an aggregated solution of P(T3-TPD) : PC71BM. Further, in order to gain insight into how the common solvent additive DIO enhances thin film morphology, in situ UV-vis absorbance and reflection spectroscopies, coupled with thin film morphology characterization, was performed to develop a mechanistic understanding of the solidification process. In situ and static measurements revealed that DIO increases the nucleation density, reducing domain size and additionally increases the polymer crystallinity and phase purity.