(381c) Device Performance of Poly(3-hexylthiophene)/Fullerene Solar Cells Is Limited By Electron Transport

Polythiophene/fullerene mixtures are studied heavily for their application in organic photovoltaic devices.  Evidence shows that performance of organic photovoltaics is dependent on the morphology of the active layer at multiple length scales.  Nevertheless, the critical morphological parameters governing device performance have not been identified in one of the most studied systems to date, mixtures of regioregular poly(3-hexylthiophene) (P3HT) with [6,6]-phenyl-C₆₁-butyric methyl ester (PCBM).  We have examined the role that morphology plays on device performance and find that phase separation within fullerene-rich domains in P3HT/PCBM active layers can strongly affect device performance.  Specifically, we have modulated the composition of the fullerene-rich domains by mixing regioregular P3HT, regiorandom P3HT (which is amorphous) and PCBM.  We find that replacing regioregular P3HT with regiorandom P3HT has little effect on device performance when spinodal decomposition driven phase separation occurs in the amorphous phases of P3HT/PCBM mixtures.  This is consistent with our previous work on characterizing electron transport in amorphous P3HT/PCBM mixtures, where we demonstrate that electron mobilites can vary by orders of magnitude with PCBM composition and is high when phase separation is present.