Progress and Challenges in Multijunction Solar Cells Utilizing Ternary and Quaternary Semiconductor Alloys

Abstract

Multijunction solar cells have emerged as a promising approach to overcome the efficiency To bypass this efficiency constraint of single-junction PV cells, a new type of cell has been developed called multijunction PV cells that can absorb multiple portions of the solar spectrum with various semiconductor layers whose bandgaps have been engineered appropriately. In this study, the development and limitations of ternary and quaternary semiconductor alloys for PV applications will be discussed and their focus will be on the heterojunction solar cells based on CuInTe₂ (ternary alloy) and Cu₂ZnSnS₄ (quaternary alloy). The devices were fabricated by electrodeposition method, where CdS was used as a buffer layer, and by optimized controlled annealing treatments to achieve the best structural and optoelectronic properties. Among the devices, the device based on CuInTe₂ achieved a maximum power conversion efficiency of ~4.13%, Voc of 480 mV, Jsc of 20 mA/cm2 and FF of 43%. The study emphasizes the key advantages of ternary alloys: high optical absorption and relatively easy composition; and quaternary alloys: high compositional flexibility and earth abundant components for low cost PV applications. But both types of materials are hampered by serious problems, including recombination losses, series resistance, interface mismatch, compositional disorder, and secondary phase formation. They can cause severe hindrance for integration in high-efficiency multijunction architectures. The results indicate that there is a need for further advances in the engineering of the interfaces, the reduction of defect densities and the tuning of the band gaps for the realization of efficient and scalable multijunction solar cells using ternary and quaternary semiconductor alloys.