The effect of excited state occupation and phonon broadening in the determination of the non-equilibrium hot-carrier temperature in InGaAsP quantum-well absorbers (Conference Presentation)

Abstract

Hot carrier solar cells (HCSCs) have been proposed as potential systems to increase the conversion efficiency of single gap solar cells beyond the Shockley-Queisser limit. Despite a great deal of recent progress in HCSCs, designing an effective and efficient hot carrier absorber remains challenging. To evaluate the efficiency of any proposed absorber accurate determination of the carrier temperature is required. This can be non-trivial, particularly in the quantum wells (QW) where state-filling effects can complicate the simple extraction of carrier temperature from photoluminescence (PL) spectra. Specifically, the PL may be distorted if there are other linewidth broadening mechanisms prevalent in addition to non-equilibrium carriers. These may include; in addition to state filling, the effects of phonons and system inhomogeneities, all of which serve to perturb the PL linewidth. In this study, an InGaAsP QW with a type-II band alignment is investigated using continuous wave power and temperature dependent PL to evaluate the effects of broadening on the extraction of the true carrier temperature in the system [1]. Since there is a relatively small energy separation between the ground and first excited state transitions in the QW studied, state filling effects can be controlled and their contribution to the linewidth evaluated, using various conditions and combinations of excitation power and lattice temperature. The role of phonons is also presented, and supported within the framework of a theoretical model that includes the various phononic processes and their temperature dependent contribution to the PL. This work is supported by the National Science Foundation Grant ECCS #1610062 [1] Esmaielpour, Hamidreza, Vincent R. Whiteside, Louise C. Hirst, Joseph G. Tischler, Chase T. Ellis, Matthew P. Lumb, David V. Forbes, Robert J. Walters, and Ian R. Sellers. Progress in Photovoltaics: Research and Applications (2017).