InGaP-based Quantum Well Solar Cells

Quantum well structures hold tremendous potential in taking next step beyond current photovoltaic structures in achieving solar conversion efficiencies beyond 50%. In this paper we investigate p-i-n InGaP solar cells incorporating InGaAsP/InGaP strain balanced multiple quantum wells (SBMQWs) to tune the absorption threshold beyond the In0.49Ga0.51P cut-off (similar to 1.85 eV). The effects of quantum well number and thickness on the optoelectronic properties of InGaAsP/InGaP SBMQWs are investigated. Specifically, we investigate the bandgap tunability of these SBMQW devices by varying well and barrier thickness. Spectral response measurements reveal that longer excitonic absorption with efficient carrier transport can be realized if proper materials compositions and thicknesses are realized. In addition, InGaP p-i-n solar cells including various numbers of InGaAsP/InGaP SBMQWs with an effective bandgap of 1.65 eV in the intrinsic (i) layer were fabricated and characterized. With up to 30 quantum wells, spectral response and light I-V measurements reveal an improvement in the excitonic absorption and short circuit current in comparison to the standard device. The promising results in this work provide an alternative path for realizing 1.5-1.8 eV subcells in next-generation multi-junction solar cells.