Ascertaining the limitations of low mobility on organic solar cell performance

In the past decade, organic photovoltaics (OPV) have emerged as an intensely studied alternative energy technology. The OPV platform presents several attractive qualities, yet, the high disorder and relative low mobility of the materials comprising OPV systems remain a bottleneck to further progress. We report here a modeling methodology that quantifies the efficiency losses engendered by the low mobility of these systems. We also report a methodology that explicitly treats the charge transfer (CT) state that has been shown to influence device performance. We compare two commonly studied OPV architectures, the bilayer (BL) and blended bulk-heterojunction (BHJ), and separately investigate the sensitivity of each architecture to mobility. Our findings suggest that mismatched mobilities of the active layer components can lead to additional recombination currents. We find that the collection current is largely limited by the slow carrier; consequently, the high mobility carriers only increase the recombination current without aiding collection.