Physics of Cu(In, Ga)Se₂ solar cells in high injection regime

Cu(In, Ga)Se₂ (CIGS) thin film microcells, operating under concentrated illumination, are studied. The advantages of such devices in terms of increased efficiency and material saving are experimentally evaluated. CIGS microcells, have diameters varying from 5 μm to 500 μm. Their optoelectronic properties are studied under laser concentrated illumination, in order to evaluate the gains that can be anticipated from operating CIGS thin film solar cells. Various experiments, such as photoluminescence, modulated photocurrent, quantum efficiency measurements are performed to gain insight into the physical properties of CIGS under concentration. The microcell structure yields significant advantages over standard thin film solar cells. Due to the reduced size of the microcells, the resistive and thermal losses are drastically decreased, enabling the use of high concentration (> 1000 suns). A significant gain in terms of material consumption is expected, which is particularly important for the CIGS technologies, relying on rare materials such as indium. A 4% absolute efficiency increase on microcells at 100 suns is observed. The open circuit voltage is increasing up to several thousand suns, to reach over 850 mV. The temperature increase is limited to less than 20°C over the ambient at concentration around 1000 suns. Devices are also tested up to ultrahigh concentrations (75000 suns), leading to current densities over 500 A/cm². Features of the high injection regime on CIGS, such as decreasing absorber series resistance, are also highlighted and modeled.