Evaluating 1 MeV proton damage in Cu(In,Ga)Se₂ solar cells and a recovery pathway

Abstract The resilience of chalcogenide-based solar cells (SCs) in the space environment is crucial for their application in satellite power systems. In this experimental study, we investigate the effects of 1 MeV proton irradiation at fluences ranging from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>3</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mo>×</mml:mo> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> to 10 14 H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mtext>+</mml:mtext> </mml:msup> </mml:mrow> </mml:math> cm −2 on the optoelectronic properties of Cu(In,Ga)Se 2 (CIGS) based SCs. In situ and ex situ electrical characterization revealed that irradiation causes degradation of the diode parameters and the electrical performance of the device, in particular the open-circuit voltage ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>V</mml:mi> <mml:mtext>OC</mml:mtext> </mml:msub> </mml:mrow> </mml:math> ), fill factor and power conversion efficiency ( η ). Fluences above 10 13 H <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mtext>+</mml:mtext> </mml:msup> </mml:mrow> </mml:math> cm −2 caused significant degradation of the SCs. Keeping the SCs at room temperature, ambient atmosphere and in the dark did not contribute significantly to the SC recovery. The photoluminescence (PL) analysis revealed an increase in the defect density leading to the formation of deeper radiative recombination channels, as well as non-radiative ones, and an increase on the magnitude of the fluctuating potentials. In order to revert this degradation, we explored a heat-light soaking (HLS) treatment that consisted in exposing the SCs to light incidence at a temperature slightly above 90 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mo>°</mml:mo> </mml:msup> </mml:mrow> </mml:math> C. This treatment significantly restored the device’s electrical performance and the luminescence properties, demonstrating partial defect annihilation and restoration of the CIGS electronic structure. Interestingly, a non-irradiated SC subjected to the same HLS treatment showed no significant beneficial effect on the performance of the SC, which confirms the link between the observed recovery of the irradiated SCs and the annihilation of irradiation-induced defects. The findings of this work suggest that HLS is an effective, space-compatible self-healing mechanism that mitigates radiation damage in CIGS SCs, potentially enabling satellite SCs to be designed without cover glass.