Observation of reduced radiative recombination in low-well-number strain-balanced quantum well solar cells

Absolute electroluminescence and photoluminescence measurements were carried out on strain-balanced quantum well solar cells. Over a range of bias, a reduced radiative recombination in the wells was observed compared to a model assuming a constant quasi-Fermi level separation (QFLS) over the device thickness. This was interpreted as a QFLS suppression in the wells relative to the bulk of 18 and 5 meV, respectively, for the single and five well strain-balanced quantum well solar cells, consistent with previous results on strained single quantum well and double quantum well devices. The photoluminescence spectra at open-circuit voltage under illumination in the well agreed with the electroluminescence spectra in the light in contrast to some theoretical predictions. Generation of hot carriers in the wells could be the thermodynamically compensating phenomenon for the QFLS reduction.