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Open circuit voltage improvement in InAs/GaAs quantum dot solar cells using reduced InAs coverage

Ten-layer InAs/GaAs quantum dot (QD) solar cells exhibiting enhanced short circuit current (Jsc) and open circuit voltage (Voc) comparable to a control GaAs p-i-n solar cell are reported. One-sun Jsc is enhanced by 3.5% compared to that of the GaAs control, while the open circuit voltage is maintained at 994 mV. Results were achieved using optimized InAs QD coverage and a modified strain balancing technique, resulting in a high QD density (3.6×1010 cm−2), uniform QD size (4 × 16 nm) and low residual strain (103 ppm). The suppression of larger, coalesced InAs islands is shown to reduce non-radiative recombination in the depletion region, reducing dark current densities. The resulting enhanced open circuit voltage is a promising result for the future of InAs QD-enhanced GaAs solar cells. The extrapolation of short circuit current density enhancement with increasing quantum dot layers is evaluated here and potential efficiencies exceed baseline GaAs values. In the final work, a twenty-period QD will be grown. The QD growth improvement used here will be applied in this case assuming a linear enhancement in Jsc and a continued suppression of voltage degradation typical of these devices. The efficiency value of this device may show the potential to exceed that of a comparable baseline GaAs cell. In order to further evaluate carrier dynamics, temperature dependent PL will be used to extract activation energies with particular focus on barrier layer material. In addition, the choice of depth placement in the i-region has been shown to give varied device results in QW solar cells. This will also be in focus for QD solar cells, as these devices continue to be studied and optimized for photovoltaic energy conversion.