Indium-dependent performance and voltage limitation in fully sputtered indium zinc oxide/CdTe solar cells

Replacing CdS as the window layer in CdTe solar cells remains a critical challenge toward environmentally benign and scalable photovoltaic technologies. In this work, we report fully sputtered IZO/CdTe solar cells by systematically varying the indium content in the IZO layer. The optimized composition (IZO-32) achieves a power conversion efficiency of 5.68%, with a high short-circuit current density of 27.5 mA·cm −2 , but a limited open-circuit voltage (V OC ≈ 0.48 V). J–V measurements are used to compare the relative performance trends among the different IZO compositions. A combined experimental and numerical approach indicates that this voltage deficit is governed not only by bulk transport but also by interface-controlled energetics. X-ray photoelectron spectroscopy (XPS) depth profiling evidences oxygen diffusion across the IZO/CdTe interface, suggesting the presence of oxygen-related CdO x /TeO x species near the IZO/CdTe transition region. This interfacial oxide is proposed to promote Fermi level pinning and to induce a metal–insulator–semiconductor (MIS)-like junction behavior. SCAPS-1D simulations incorporating a thin interfacial layer, representing the oxygen-rich transition region identified by XPS, reproduce the main experimental trends and are consistent with barrier-mediated, tunneling-assisted transport, in which photocurrent is partially preserved while the voltage output remains limited. These results suggest that the performance of all-sputtered IZO/CdTe solar cells is strongly constrained by interface chemistry rather than by bulk IZO optimization alone, providing a pathway for future interface engineering strategies.