Binary Solvent Additives Treatment Boosts the Efficiency of PTB7:PCBM Polymer Solar Cells to Over 9.5% (Solar RRL 4∕2018)

Abstract

In this work, a 9.5% of power conversion efficiency (PCE) is obtained in the thieno [3,4-b] thiophene/benzodithiophene (PTB7): (6,6)-phenyl-C70-butyric acid methyl ester (PC70BM) based polymer solar cell (PSC) by using a novel binary solvent additive of diphenyl ether (DPE): 1,8-diiodoctane (DIO). We find that this binary solvent additive approach increases the PTB7 donor crystallinity using DPE and enhances the PC70BM dispersion using DIO. This amended aggregation results in a better donor/acceptor phase separation. We show that the improved crystallization and face-on orientation preference of PTB7 contributes to higher light absorption and charge transport efficiency in the active layer. Moreover, a better D/A phase separation provides more efficient charge extraction and suppresses the charge recombination, leading to an improved FF >70%.