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

International audienceAbsolute electroluminescence and photoluminescence measurements have been carried out on strain-balanced quantum well solar cells (SB-QWSCs). Over a range of bias, 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 5 well SB-QWSCs, confirming previous results on strained Single Quantum Well (SQW) and Double Quantum Well (DQW) cells. The photoluminescence spectra at open-circuit voltage when illuminating 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. When a p-n junction solar cell is illuminated and/or biased the Fermi level splits into electron and hole quasi Fermi Levels at least over the depletion region of the device