Back contacts materials used in thin film CdTe solar cells-A review

CdTe is the leading commercial thin film photovoltaic technology with current record laboratory efficiency (22.1%). However, there is much potential for progress toward the Shockley-Queisser limit (32%). The best CdTe devices have short-circuit current close to the limit but open-circuit voltage has much room for improvement. Back contact optimization is likely to play a key role in any improvement. Back contact material choice is also influenced by their applicability in more complex architectures such as bifacial and tandem solar cells, where high visible and/or near-infrared transparency is required in conjunction with their electrical properties. The CdTe research community has employed many back contact materials and processes to realize them. Excellent reviews of back contacts were published by McCandless and Sites (2011) and Kumar and Rao (2014). There have been numerous publications on CdTe back contacts since 2014. This review includes both recent and older literature to give a comprehensive picture. It includes a categorization of back contact interface materials into groups such as oxides, chalcogenides, pnictides, halides, and organics. The authors attempt to identify the more promising material groups. Attention is drawn to parallels with back contact materials used on other thin film photovoltaics such as perovskites and kesterites.

Automated summary

CdTe is currently the leading commercial thin film photovoltaic technology, but there is much potential for progress towards the Shockley-Queisser limit. Back contact optimization and material choice are critical factors in improving efficiency. Research has explored various back contact materials and processes to identify the most promising groups for further development. Comparisons are drawn with back contact materials used in other thin film photovoltaics like perovskites and kesterites.