Design and performance analysis of an efficient GaAs/AlGaAs heterojunction bipolar transistor solar cell

Abstract

In this work, we propose a highly efficient three-terminal heterojunction bipolar transistor solar cell. We have chosen GaAs/AlGaAs material system in this regard for its excellent optoelectronic properties. Rigorous optical and electrical performance analysis through computer simulation has been carried out to characterize the designed device. Usually, the efficiency of the solar cell depends on material composition, absorption of light, carrier transport, recombination etc. In our proposed structure, we have optimized these parameters to enhance the efficiency to a maximum value of 35.6%. We have determined the optimum layer thickness for the designed cell by varying the layer thickness of different regions of the structure and calculating efficiency through optoelectronic simulation. We have also changed the doping of three regions and found out the doping concentration for which the efficiency is maximized. We further investigated the effect of different loss mechanisms (recombination) that occur inside the solar cell and find out the dominant loss mechanism. We have also examined the role of photon recycling effect on the performance of designed solar cell. Finally, we have compared our result with conventional heterojunction solar cell and shown that this novel three-terminal device yields higher efficiency. The analysis and results presented in this thesis would provide a clear guideline for designing HBT based photovoltaic devices.