R.E. Welser, A.K. Sood, N.K. Dhar
Magnolia Optical Technologies, Inc.,
Keywords: photovoltaics, quantum well solar cell
Summary:Thin-film III-V devices are an attractive technology for photovoltaic energy harvesting devices, capable of supplying portable and mobile power in both terrestrial and space environments. Single-junction III-V technologies can provide high levels of performance over a wide range of operating conditions and minimize costs by limiting the required volume of epitaxial material. The most efficient single-junction thin-film III-V cells reported to date have employed high performance back reflector structures. The back reflector effectively restricts the angular profile of the radiative emissions from the III-V cell, which can enhance the voltage output of cells operating at or near the radiative limit. In this paper, we will discuss strategies for further restricting radiative emissions and achieving single-junction III-V thin-film cells with efficiencies approaching 40%. In particular, the use of nanostructured layers in the absorber layer provides a pathway for realizing advanced photovoltaic device concepts with higher conversion efficiency. Over the past several decades, nanostructured III-V quantum well and quantum dot solar cells have been investigated as a means of implementing advanced device concepts to improve solar cell efficiency. Previous work in the field of quantum well solar cells has also shown that the radiative emissions from strained InGaAs well are not necessarily isotropic, but instead can exhibit a partially restricted emission profile. Detailed balance calculations suggest that restricted radiative emissions can have a significant impact on the open circuit voltage and efficiency. In this paper, we review the impact restricted angular emissions can theoretically have on solar cell performance, and discuss how advanced nanostructured absorber layers in combination with high performance back reflector structures can be employed to realize next generation photovoltaic devices leveraging restricted angular emissions.