Novel HIT Cell Design: GaAs/Ge Stacked Solar Cell

Abstract

The massive growth in the energy consumption and in the CO2 emission arise the need of the world to clean and renewable sources of energy such as solar energy. Many researches approved the strong potential of Abu Dhabi for solar energy capture which led to many successful solar energy projects such as Masdar city. However, the high cost of photovoltaic reduces its effectiveness when compared to fossil fuels. Therefore, to achieve the grid parity with the fossil fuels, maximizing the conversion efficiency with minimal cost is needed. Heterojunction with intrinsic thin layer (HIT) thin film solar cell is one of the effective solutions to the high cost of crystalline silicon (c-Si) photovoltaic. The thin intrinsic layer of hydrogenated amorphous silicon (a-Si:H) passivates the substrate layer (c-Si); however, interface trap density (Dit) are formed in the a-Si:H/c-Si interface. In the first part of this work, we used Physics Based TCAD Simulations to study how the quality of the a-Si:H/c-Si interface (Dit) could affect the change of the solar cell performance with the change of the main design parameters. The results have showed the dependency of the open circuit voltage (Voc) and the independency of the short circuit current (Jsc) on the interface quality. Also, the susceptibility to change of the HIT cells performance rises as the quality of the interface of the HIT solar cell increases. In the second part of the thesis, we designed a GaAs/Ge single junction stacked thin-film solar cell and studied the performance in different cases of doping levels and thicknesses. Due to the limitation of the bandgap (Eg) of the semiconductors materials, the solar cell with a single junction can merely absorb the solar radiation equal to or higher than its bandgap. Tandem solar cell is one of the successful techniques that have been used to widen the utilized spectrum by combining different materials with different bandgaps. Comparing to the structure of a single junction of GaAs thin film cell, the results show an increase in (Voc) and (Jsc) up to 7% and 12% respectively, which enhanced the absolute efficiency by 4% with the Ge layer.

Date of Award	Jul 2014
Original language	American English
Supervisor	Ammar Nayfeh (Supervisor)