Native oxide growth on polycrystalline undoped CdSeTe/CdTe surfaces and its impact on solar cell performance

Abstract

Ambient air exposure between the absorber (CdTe) and back contact (Te layer) deposition was varied to control the native oxide formation on CdTe surface. A short air exposure period (~ 30 min) led to an improvement in open-circuit voltage (Voc) by 60 mV as compared to the device with minimal ambient air exposure, and enabled power conversion efficiency (PCE) reaching > 17.5 % in devices with no intentional doping (undoped). In contrast, 1-day exposure resulted in a kink in the J-V, indicating a barrier formation. X-ray Photoelectron Spectroscopy (XPS) analysis verified a native oxide formation on the absorber surface. One month air exposure post acid etch did not exhibit an s-kink in the J-V but severe kink was observed for unetched surface exposed under identical conditions. Notably, XPS analysis indicates an oxide layer on etched as well as unetched surface. This suggests that nature of the oxides formed on these surfaces may not be identical.