Enhanced Photovoltaic Efficiency by Heterojunction Assisted Impact Ionization


Charge multiplication by impact ionization (II) produces ~1% of the photogenerated charge in silicon photovoltaic (PV) devices under solar illumination and ~30% for photons above the silicon direct band gap. Despite these observations, few efforts have been reported to find materials and structures that optimize the rate of II and thereby convert a larger fraction of the solar spectrum to useful electrical energy. In contrast, the dramatically increased rate of II near band offsets in reverse-biased heterojunctions has been used extensively to improve the efficiency of avalanche photodiodes. By combining and expanding these existing technologies, Prof. Stephen Kevan and Prof. Dave Cohen's work will provide both a simple and practical route to improving the conversion efficiency of existing PV devices, as well as a broadly applicable approach to overcoming the Shockley-Queisser limit in next-generation PV materials. HAII promises eventually to improve the power conversion efficiency of PV devices by as much as a factor of two.

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Patent Information:
For Information, Contact:
Christine Gramer
Senior Technology Development Associate
University of Oregon
Stephen Kevan
Dave Cohen
Materials Science
Nanoscience & Microtechnologies