Development of indium arsenide quantum dot solar cells for high conversion efficiency
Sunlight is the largest energy source available on earth. Under clear conditions there is approximately 1,000 watts per directly incident square meter, which reaches the earth everyday. Solar cells are devices that can be used to collect such abundant form of energy and convert it into electrical energy for daily consumption. Therefore, it is important to research this subject in order to obtain high efficiency solar cells. In this thesis InAs quantum dot (QD) solar cells are studied and investigated. The theory of using QDs as an intermediate band in GaAs-based solar cells is introduced. Three samples are grown for investigation, an MBE grown GaAs control cell, an MBE grown six-stack InAs QD solar cell, and an MOCVD grown three-stack InAs QD solar cell. Inductively coupled plasma (ICP) etch without Si3N4 sidewall passivation and wet etch using Si3N4 sidewall passivation are implemented to process the solar cells, to study the effects of processing on the device performance. Spectral response measurements show photocurrents above the GaAs wavelength indicating the contribution from the InAs QDs in the structure. From the I-V measurements, efficiencies for the GaAs control cell, MBE six-stack InAs QD, and MOCVD three-stack InAs QD solar cells are 8.95%, 6.55%, and 1.33%, respectively. Wet etching with Si3N4 sidewall passivation shows slightly higher efficiency for the MBE six-stack sample. Sizing effects of the 5x5mm, 3x3mm, and 2x2mm for the MBE grown six-stack InAs QD solar cells show that the device efficiency and open circuit voltage do not change with size. The 2x2mm solar cell exhibits improvement in the ideality factor, shunt resistance, and saturation current. Some future work suggestions are given to increase the InAs QD solar cells such as multilayer structures with embedded InAs QD using different processing techniques.
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