The Impact of Carrier Delocalization and Interfacial Electric Field Fluctuations on Organic Photovoltaics

Abstract

Organic photovoltaic (OPV) devices hold a great deal of promise for the emerging solar market. However, to unlock this promise, it is necessary to understand how OPV devices generate free charges. Here, we analyze the energetics and charge delocalization of the interfacial charges in poly(p-phenylenevinylene) (PPV)/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene-2,5-diyl) (P3HT)/PCBM devices. We find that, in the PPV system, the interface does not produce molecular disorder, but an interfacial electric field is formed upon the inclusion of environmental polarization that promotes charge separation. In contrast, the P3HT system shows a significant driving force for charge separation due to interfacial disorder confining the hole. However, this feature is overpowered by the polarization of the electronic environment, which generates a field that inhibits charge separation. In the two systems studied herein, electrostatic effects dominate charge separation, overpowering interfacially induced disorder. This suggests that, when balancing polymeric order with electrostratic effects, the latter should take priority.