CdTe Photovoltaics in Superstrate Geometry–Back-Contact Materials: A Review

Cadmium telluride (CdTe) and copper–indium–gallium diselenide are the only commercialized cells among the various thin-film photovoltaic devices. While checking the ability of CdTe, we can identify the untapped potential of this material from the difference in the theoretical and practical limits of the photoconversion efficiency (PCE). One of the main reasons behind this untapped potential is the difficulty in developing a proper quasi-ohmic back contact because most commonly used conductors tend to develop a Schottky barrier at the CdTe/metal interface. Even though the presence of copper boosts the device's efficiency, it also depletes the long-term stability of the device by diffusing it into the main body of the device. The non-cupric back contacts introduced did not produce the expected outcome because they also showed some instability and did not enhanced the PCE. The weakness must be identified and appropriately addressed, with advancements occurring as time passes to strengthen the performance of CdTe solar cells. Hence, in this review, we try to identify the issues related to the CdTe thin-film solar cells and the materials used as a back contact in the superstrate configuration to benefit further research.