Evidence of suppressed hot carrier relaxation in type-II InAs/AlAs_1-xSb_x quantum wells

Hot carrier solar cells (HCSCs) have been proposed as devices, which can increase the conversion efficiency of a single junction solar cell above the Shockley-Queisser limit. For practical implementation of such systems, solar cells operating with efficient hot carrier extraction must circumvent two fundamental challenges: 1. Find an absorber material in which hot carriers are sustained either via inhibiting or circumventing phonon relaxation pathways; 2. Implement energy selective contacts in which only a narrow range of energy within the hot carrier distribution is extracted; thereby, reducing cooling losses in the contacts. Here, type-II InAs/AlAs_0.16Sb_0.84 quantum-wells are investigated as a candidate system for hot carrier absorbers. Continuous wave power and temperature dependent photoluminescence measurements are presented that indicate: a transition in the dominant hot carrier relaxation process from conventional phonon-mediated carrier relaxation-below 90 K-to a regime where inhibited radiative recombination dominates the hot carrier relaxation-at higher temperatures¹. The reduction in the PL efficiency is strongly coupled to an increase in the hot carrier temperature extracted from the measurements. This behavior is attributed to a build-up of electrons in the QWs, which appears to inhibit electron-phonon relaxation².