Effect of Gallium Content on Diode Characteristics and Solar Cell Parameters of Cu(In1-xGax)(Se0.98Te0.02)2 Thin Film Solar Cells Produced by Three-stage Co-evaporation at Low Temperature

Abstract

In this study, Cu(In1-xGax)(Se0.98Te0.02)2 thin film solar cells with x values of 0.17, 0.20, 0.23, and 0.26 were successfully produced by three-stage co-evaporation technique at low temperatures. The diode characteristics and solar cell parameters of thin film chalcopyrite solar cells with the structure of SLG/Mo/Cu(In1-xGax)(Se0.98Te0.02)2/CdS/ZnO/ITO/Ni-Al-Ni were investigated by current-voltage measurements. The ideality factor, series resistance, and barrier height were obtained by the Cheung-Cheung method using the current-voltage results measured in the dark at room temperature. Open-circuit voltage, short-circuit current density, fill factor, and the power conversion efficiency of the thin film solar cells were derived from the current-voltage measurements realized by a four-point measurement setup under AM1.5G standards at room temperature. It was found that the increase in the gallium content first decreased the ideality factor, however, it increased again after exceeding the x value of 0.23. While the amount of gallium was increasing, fluctuations were observed in the series resistance values. The barrier height first increased with the increasing amount of gallium and decreased after exceeding the x value of 0.23. The solar cell parameters increased by increasing the x value up to 0.23 and decreased after exceeding this point. It was found that the diode parameters have an effect on each other but the most effective diode parameter was the ideality factor. The efficiency of the Cu(In1-xGax)(Se0.98Te0.02)2 thin film solar cells was increased from 3.7% to 6.3% by increasing the x value from 0.17 to 0.23.