Photovoltaic power generation can be improved by keeping the electrons hot

Carriers, be they electrons or holes or electron-hole pairs, can improve the power conversion efficiency of solar cells if they can be extracted at elevated energies, i.e. when they are still “hot.” One possible pathway to accomplishing this is to inhibit the relaxation mechanisms present in the solar cells, reducing the power losses of the photogenerated hot carriers via thermalization.

Esmaielpour et al. investigated type-II InAs/AlAs_0.16Sb_0.84 multi-quantum well structures to study the impact of the phononic properties of the AlAsSb barrier material in hot carrier thermalization losses.

They observed through experiments that a thicker AlAsSb barrier, facilitated by increasing AlAsSb concentration and decreasing the InAs content in the superlattices, led to a decrease in the relaxation rate of the hot carriers by the introduction of a “phonon bottleneck.” The bottleneck reduces the decay rate of the optical phonons, which increases the population of hot phonons, thus keeping the carriers hot for a longer period of time.

According to the authors, their discovery not only means that AlAsSb barriers are effective in inhibiting thermalization loss for carriers, but can also be used to activate or control the properties of the phonon bottleneck by design.

“The inhibition of hot carrier relaxation by phonon engineering acts at a highly multidisciplinary interface, linking condensed matter physics, materials science and electrical engineering disciplines,” said author Hamidreza Esmaielpour. “In addition, it opens up potential avenues for the realization of high efficiency single-junction solar cells.”

Source: “Hot carrier relaxation and inhibited thermalization in superlattice heterostructures: the potential for phonon management,” by Hamidreza Esmaielpour, Brandon K. Durant, Kyle R. Dorman, Vincent R. Whiteside, Jivtesh Garg, Tetsuya D. Mishima, Michael B. Santos, Ian R. Sellers, Jean-François Guillemoles, and Daniel Suchet, Applied Physics Letters (2021). The article can be accessed at http://doi.org/10.1063/5.0052600 .

This paper is part of the Scalable Ways to Break the Efficiency Limit of Single-Junction Solar Cells Collection, learn more here .