Nanowire Solar Cell Sensitized with II-VI Quantum Dot Layer

Abstract

We report first results on a new solar cell consisting of a p-i-n hetero-junction formed between n-type transparent nanowires, undoped semiconductor quantum dots and a wide bandgap p-type polymer layer. The overall structure is SnO₂/ZnO/CdSe/MEH-PPV with MEH-PPV standing for poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]. Microscopic studies on the structure of the quantum dot layer before and after anneal indicates a morphology change from a quantum dot assembly to a continuous polycrystalline thin film. The charge transfer between the absorber layer and the adjacent layers is improved as the layer is converted from the quantum dot assembly towards a polycrystalline thin film structure. In optimized devices the spectral photocurrent response shows contributions from the ZnO, the CdSe and the MEHPPV, covering the spectral range from 300 to 700nm with an external quantum efficiency between 30 and 40%. The overall energy conversion efficiency approaches 1%.