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Valley Photovoltaics: Towards the Realization of Ultra-High Efficiency Solar Cells

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April 20, 2020

Valley Photovoltaics: Towards the Realization of Ultra-High Efficiency Solar Cells

physical diagram
Mechanism for Effective Hot Carrier Extraction in III-V systems

Experimental condensed matter physicists in the Department of Physics at OU have developed an approach to circumvent a major loss process that currently limits commercial solar cells to conversion efficiencies less than 30 %. In this new approach, recently published in the journal Nature Energy, members of the Photovoltaic Materials & Devices Group led by Dr. Ian Sellers along with theorists at Arizona State University (David K. Ferry), have demonstrated a breakthrough towards the long-sought Hot Carrier Solar Cell, a device in which high energy photo-generated charge carriers are extracted prior to heat generation (device losses) with predicted efficiencies in excess of 50%.

Although this device has been the source of a considerable amount of research over the last 10-15 years, the realization of a practical solution has thus far eluded researchers with proof-of-principle demonstrations only presented under unrealistic conditions (low temperature and/or high power laser excitation) or in materials and structures not relevant for solar cell operation (mismatched to the solar spectrum).

In the OU-ASU approach, the full band structure of the absorbing semiconductor material is manipulated, and “hot” high energy photo-generated carriers absorbed through a direct transition in the conduction band (G-valley) rapidly transfer to higher energy valleys (L or X) in the conduction band, which provides a route to inhibit carrier thermalization, i.e., heat generation. This new approach has led to the experimental demonstration of hot carrier effects in a simple solar cell structure under conventional solar irradiation conditions at room temperature. These results, therefore, represent significant progress in the realization of the hot carrier solar cell, and the potential for ultrahigh efficiency single semiconductor devices ‒ which would revolutionize the field of photovoltaics and renewable energy generation, in general.