Enhancing Open-Circuit Voltage and Efficiency of Shallow InxGa1-xAs Quantum Well GaAs Solar Cells

Abstract

In this work, we present an extensive study of the varied parameters of In x Ga 1-x As quantum well (QW) GaAs solar cells. First, by optimizing the doping in the GaAs base of the solar cell we were able to demonstrate a device with triple strained coupled In 0.06 Ga 0.94 As/GaAs with open-circuit voltage (V oc ) of 1.052 V and 22.6% AM0 efficiency. We studied the performance of In x Ga 1-x As/GaAs 0.68 P 0.32 strain balanced QW solar cells with x = 6%, 8%, 10%, and 14% and an increased number of superlattice periods. The deterioration of the superlattice interface quality in the strain balanced QW structures was diagnosed with X-ray diffraction. We observed that having strain balancing was beneficial for the 3-layer shallow QW solar cells’ performance, improving the spatial uniformity and maintaining high V oc . It was noted, however, that in the cells with a 12-period In 0.10 Ga 0.90 As/GaAs 0.68 P 0.32 and In 0.14 Ga 0.86 As/GaAs 0.68 P 0.32 superlattices, adding strain balancing had a dramatic impact on their overall performance increasing the dark current by up to 3 orders of magnitude and reducing the V oc by up to 197 mV. Reduction of the V oc in strain-balanced solar cells was correlated with the morphological degradation of the QW structures caused by the excessive step bunching, and implementing 17 nm-thick GaAs 0.90 P 0.10 strain balancing allowed to partially recover the planar QW growth resulting in V oc retention over 1 V in the cells with 12 QWs.