Impact of GaAsSb Capping Layer on the performance of InAs Quantum Dots Solar Cells

Quantum dot solar cells (QDSCs), based on semiconductor materials, hold potential for improved performance by capturing a broader portion of the solar spectrum. In particular, InAs quantum dots (QDs) covered with a thin GaAsSb capping layer are promising for enhancing GaAs solar cell efficiency. Despite their advantages over standard InAs QDs, the carrier transport and recombination mechanisms in these modified QD structures are not yet fully understood. This Master Thesis conducts an optoelectronic analysis of solar cells containing various GaAs1-xSbx/InAs QD structures to understand the transport and recombination mechanisms and evaluate performance under diverse conditions. The study is divided into two parts. Firstly, the properties of solar cells at room temperature are analysed, focusing on the effect of Sb concentration in the capping layer on recombination mechanisms, absorption edges, energy conversion efficiency, and unintentional doping concentrations. The second phase involves temperature-dependent measurements from 330 K to 25 K to explore carrier dynamics and efficiency loss mechanisms. Various illumination conditions are assessed. Current – voltage (IV) characteristics were measured under dark conditions, 1 sun AM1.5G, and 2 suns AM1.5G illumination. IV measurements under 1 sun AM1.5G with a GaAs filter were also performed to isolate the contribution of the multilayers chosen samples made up by 10 QDs layers in the GaAs p-i-n junction. The results indicate that low concentrations of Sb can enhance efficiency, while high concentrations of Sb can cause non-radiative recombination losses. The study also shows that transport phenomena vary with temperature. Additionally, QD presence and their specific band structures, influenced by the capping layer composition, lead to higher efficiencies under increased power due to saturation of the nanostructures. This comprehensive optoelectronic analysis allows to assess QDSCs for applications as single junction solar cells, multi-junction solar cells, concentrator solar cells and in-space devices, where high efficiency, lightweight design, and resilience to extreme conditions are critical.