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

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.