Characterization of charge collection in photodiodes under mechanical strain: comparison between organic bulk heterojunction and amorphous silicon

Abstract

The photo- and dark currents of organic bulk heterojunction and amorphous silicon photodiodes are measured during bending to determine the effects of mechanical strain on electrical properties. Charge collection is evaluated by the photogenerated carrier mobility-lifetime product (mt), and within the strain-failure limits, mt remains constant in amorphous silicon, while in organic heterojunction mt is shown to increase with tension and decrease with compression. By examining the optical absorption edge, the distribution of tail states in the highest occupied molecular orbital level is observed to shift indicating strain-induced disorder in the organic blend. Abrupt device failures are observed beyond 0.17% strain (20 mm curvature radius) for amorphous silicon and 0.86% (7.5 mm curvature radius) for organic semiconductors.