Quantum Well Solar Cells: Principles, Recent Progress, and Potential

Quantum well solar cells, as a promising approach for next-generation photovoltaic technology, have received great attention in the last few years. Recent developments in materials growth and device structures of quantum wells have opened up new avenues for the incorporation of quantum well structures in next-generation III/V multi-junction solar cells. In this paper, the advantages and challenges of growing quantum wells in the unintentionally doped (i) region of p-i-n solar cells are reviewed. We focus on the recent progress in 1.1-1.3 eV strain-balanced InCaAs/GaAsP, 1.6-1.8 eV strain-balanced and lattice-matched InGaAsP/InGaP, and >2.1 eV strained InGaN/GaN quantum well solar cells, including optimization of the quantum well growth conditions and improving the solar cell structure. For each material system, the challenges associated with materials growth and device performance such as critical layer thickness constraints, strain balance, bandgap tunability, and carrier transport limitations, are discussed. The performance of each quantum well solar cell is compared with bulk absorber operating in the same bandgap range, with the advantages of each being highlighted. The effect of the unintentional background doping on carrier collection (by drift) is presented through modeling and recent experimental results. The recent strategies to enhance the electric field distribution across the quantum well region are reviewed. The potential of incorporating quantum well structures in next-generation multi junction devices is also discussed.