Proton Irradiation on Cesium‐Fluoride‐Free and Cesium‐Fluoride‐Treated Cu(In,Ga)Se2 Solar Cells and Annealing Effects under Illumination

Abstract

Several studies have been performed on proton irradiation onto alkali‐metal untreated Cu(In,Ga)Se2 (CIGS) solar cells. However, there are almost no studies describing similar effects on alkali‐treated CIGS solar cells. With this motivation, this work investigates proton irradiation and annealing effects under illumination on cesium‐fluoride‐free (CsF‐free) and CsF‐treated CIGS solar cells. Both CsF‐free and CsF‐treated CIGS solar cells degrade under proton irradiation. External quantum efficiency measurements show degradation in long wavelengths after the treatment. The experimental data are fitted with a simulation, which show that proton‐irradiated degradation is more severe at high fluence. Capacitance–voltage measurements show a broadening of the depletion region after proton irradiation, which is due to the decreased net carrier concentration. It is proposed that proton irradiation at low fluence generates shallow‐type defects, whereas high‐fluence protons generate deep defects. However, it is observed that room‐temperature storage of the proton‐irradiated solar cells causes partial recovery. Thermal annealing under illumination treatments is found to be beneficial to the drastic recovery of the performance of solar cells irradiated at low fluence. High‐fluence proton‐irradiated solar cells undergo minor recovery.