Effective regulation of the micro-structure of thick P3HT:PC71BM film by the incorporation of ethyl benzenecarboxylate in toluene solution

Abstract

In this work, ethyl benzenecarboxylate (EB) was creatively selected as the additive in a blend of poly(3-hexylthiophene)/phenyl-C71-butyric acid methyl ester (P3HT/PC₇₁BM) in non-halogenated solvent toluene (TL). With the optimized incorporating concentration of EB (i.e. 2 vol%) in toluene, a great power conversion efficiency (PCE) enhancement of 4.11% was achieved without thermal annealing, whereas a maximum PCE of 4.82% with thermal annealing was achieved under the same conditions. According to our systematic characterization results, we could conclude that we successfully regulated the micro-structures, including phase separation, the domain sizes of P3HT or PC₇₁BM and the crystallinity of P3HT by incorporating 2 vol% EB in TL solution. The effectiveness of EB as a TL additive in P3HT/PC₇₁BM can be interpreted based on its Hansen solubility parameters (HSPs) and its high boiling point.