Investigation and Mitigation of Sputter Damage on Co‐Evaporated Cu(In,Ga)Se2 Absorbers for Photovoltaic Applications

Abstract

Herein, the detrimental impact of radio frequency (RF)‐sputtering on bare Cu(In,Ga)Se2 photovoltaic absorbers in view of vacuum‐deposited buffer layers is evaluated, and the possible mitigation strategies are explored. Carrier lifetimes are measured using time‐resolved photoluminescence before and after buffer deposition and exposure to the plasma environment. When directly applied on bare Cu(In,Ga)Se2 absorbers, RF‐sputtering is severely limiting the device performance, with oxygen ions emanating from the target having a stronger effect than argon ions from the process gas. The possibilities to avoid sputter damage by atomic layer deposited Zn1−xMgxO and chemical bath deposited CdS buffer layers are shown, and the ability of the latter to restore damaged surfaces is highlighted. Absorber performance is also investigated for absorbers stored in air, N2, or ultra‐high vacuum. The reduction in carrier lifetime is reflected in the reduced open‐circuit voltage of solar cells. SCAPS simulations are used to investigate possibilities to minimize the effect of sputter damage. Finally, options on how to minimize sputter damage during buffer deposition as well as on how to modify the absorber to be less sensitive are discussed.