Greenhouse Effect in Photovoltaic Cells to Enhance Efficiency of Power Beam Conversion
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.658
Greenhouse Effect in Photovoltaic Cells to Enhance Efficiency of Power Beam Conversion Andrei Sergeev1, Andrew Hewitt1, Harry Hier1, C. Mike Waits1, Myles A. Steiner2, and Kimberly Sablon3 1
U.S. Army Research Laboratory, Adelphi, MD 20783, USA
2
National Renewable Energy Laboratory, Golden, CO 80401, USA
3
Office of the Deputy Assistant Secretary of the Army for Research and Technology, Arlington, VA, USA
Recent progress in semiconductor materials with minor nonradiative recombination has stimulated investigations of novel photovoltaic (PV) converters with optical control of radiative emission. Angle restricted emission was experimentally demonstrated in PV devices with external photon recycling due to specific photonic crystals or mirrors. In this work we investigate the power beam conversion by the cell with front “greenhouse” filter, which transmits the laser light, but recycles the low energy bandgap quanta emitted by the semiconductor cell. We calculate the limiting characteristics of the greenhouse PV converters and optimize design of the converter taking into account the nonradiative recombination processes. In optimized devices addition of the greenhouse filter can increase power beam conversion efficiency by several percent.
INTRODUCTION The photo-induced current is determined by the difference between the photocarrier generation rate and photocarrier recombination rate, which includes radiative and nonradiative recombination processes. During many years the photovoltaic research focused on light absorption and fabrication of defectless materials to enhance the photocarrier generation and to reduce nonradiative processes, which significantly dominated over the radiative recombination processes. Only recently some III–V solar cells, mainly GaAs devices, have achieved values of the external luminescence quantum yield (external radiative efficiency) of 20 – 30%. High quality PV materials inspire research aimed at suppression of radiative emission from a solar cell due to external
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photon recycling. The angle restricted emission was proposed and theoretically investigated in [1].
Fig. 1. The PV converter with the greenhouse filter that reflects high energy photons and traps the low energy photons (left). Band diagram of the converter with the photonic bandgap established by the greenhouse filter.
In Ref. 2 – 3, various optical tools were used to restrict the light emission angles by reflecting the emitted photons back to the cell. In Ref. 1, the light emission was suppressed by the photonic crystal placed at the front surface of the GaAs cell. In Ref. 3, in a wide angle range the light emitted from the cell was reflected back by high quality mirror dome. The solar beam radiation w
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