Microstructural Passivation of Patterned Al₂O₃ Back Contacts on CdS/CdTe Solar Cells

Abstract Patterned aluminum oxide (Al₂O₃) back contact on cadmium telluride (CdTe) solar cells can effectively mitigate the loss of the majority carriers while retaining the passivation benefits for minority carriers. This study investigates the impact of the point‐contact geometry on cell performance, where the spacing of the microholes is systematically varied at a constant microhole diameter (≈16 µm). Microhole arrays are created on an evaporated Al₂O₃ layer (≈30 nm) on CdTe using laser‐beam lithography and selective wet etching processes. Comparative analysis indicates a significant decrease in fill factor (FF) and short‐circuit current (I_SC) when the contact fraction falls below 30%, likely due to the Al₂O₃ barrier impeding majority carriers. Above this fraction, FF and I_SC are comparable to those of baseline CdTe cells without Al₂O₃. Open‐circuit voltage (V_OC) shows a gradual decrease as Al₂O₃ coverage is reduced but exhibits a slight increase (<15 mV) when the contact fraction exceeds 30%. Cathodoluminescence (CL) characterization reveals that significantly improved radiative recombination occurs within the CdTe grain bulk with Al₂O₃, whereas this effect on grain boundaries is minimal. The findings imply complex local carrier dynamics in the patterned back‐contact region, closely tied to the microstructural properties of CdTe‐based solar cells.