Temperature-dependent Current-Voltage Characteristic of GaAsBi/GaAs Multiple Quantum Wells for Solar Cell Applications

GaAsBi has the potential to become a 1eV solar cell for the multi-junction solar cell application. GaAsBi possessed a large band gap bowing coefficient in GaAs material. It reduces the band gap's energy by 70-90 meV per unit strain for each 1% incorporation of Bismuth (Bi) into the GaAs material and produces good electron mobility properties. Research has shown its capability to extend the absorption edge above 1000 nm, higher than InGaAs junction solar cell. The previous study mostly reported the characteristic of GaAsBi p-i-n at room temperature. However, the practical operating temperature of the solar cell during sunlight is more than 60 oC. The solar cell temperatures are getting hotter as the devices are operated under concentrated sunlight. Therefore, the investigation of temperature-dependent properties for GaAsBi will contribute to providing the characteristic performance of GaAsBi solar cells at high temperatures.

The study comprises three main parts. Firstly, is to investigate the dark current performance of the GaAsBi in bulk and multiple quantum well structure devices. The dark current is important to verify the conventional current diode behaviour and quality of the growth devices. Growing the GaAsBi at optimum growth temperature is important to obtain good solar cell performance. Besides, MQW devices perform lower dark currents than bulk series devices. The second observation is to model and estimate the MQW GaAsBi under a monochromatic light source. Based on photocurrent measurement at different temperatures, several mathematical processes are conducted to produce solar cell parameters at different temperatures. The devices were also tested under a solar simulator to observe the overall performance. The third outcome is to study the carrier trapping thermal escape time of the hole carrier under the illumination of light bias at a lower temperature. The hole carrier has a longer thermal escape time than the electron carrier due to the increment of the valance band for bandgap reduction.

The results suggest many opportunities to improve the performance of GaAsBi multiple quantum. Obtaining optimum performance of GaAsBi at high temperatures, especially under solar contractor application, requires several areas of improvement, such as the growth process, number of optimum quantum well and temperature effect. GaAsBi can become a potential 1eV junction solar cell in future.