Integration of metal oxide inorganic materials into GaAscell technology as electron selective emitter layer

In recent years, electron selective carrier contacts (ESC) have emerged as an effective alternative to doped p-n heterojunction solar cells. In this thesis study, ESC layers were integrated into a flexible thin-film GaAs solar cell fabricated by the ELO method for the first time. TiO2 and ZnO were used as ESC layers. The proposed device structure reduces the complexity and cost of epitaxially grown cells while enabling the production of high-efficiency GaAs solar cells that are easy to fabricate. Within the scope of this thesis, simulations were performed for p-GaAs/TiO2, p-GaAs/ZnO and p-GaAs/TiO2/ZnO hibride device structures. The simulation results show that the use of thin TiO2 or ZnO layers instead of n-GaAs emitter layer improves the electron selectivity in GaAs solar cells, leading to high efficiency. Even without any anti-reflection layer, calculations show that high conversion efficiencies of 29.3% for p-GaAs/TiO2, 27.2% for p-GaAs/ZnO and 28.8% for p-GaAs/TiO2/ZnO can be obtained from GaAs/ESC cells. With a good anti-reflection layer, these values can approach the 32% limit. From these theoretically calculated cell structures, flexible thin film GaAs/ESC cells were successfully fabricated and characterized for the first time. However, contrary to the theoretical expectation, very high efficiency could not be measured from these fabricated cells. The highest efficiency value obtained experimentally was 2.23%. The very low shunt and very high series resistance caused by the fabrication processes and ESC coating methods led to very low open circuit voltage and fill factors of the fabricated cells, limiting the cell performance.