Cd-free kesterite solar cells featuring TiO2 as buffer layer

The results of the research published in ACS Materials Letters
scheme of a kesterite/titania solar cell

Among the most promising emerging photovoltaic technologies, we find sulfide-based kesterite (Cu2ZnSnS4): a p-type, environmentally sustainable semiconductor, based on earth-abundant elements, showing excellent characteristics especially in terms of absorption coefficient. However, inner defects of the material and a non-optimal band alignment with the highly toxic CdS (conventionally used as n-type semiconductor partner) limit the device performances to record efficiencies not exceeding 11%. Due to these reasons, several efforts need to be made in order to find a suitable alternative to CdS buffer layer. TiO2 has been recently suggested as a promising alternative to CdS in CZTS solar cells. Nevertheless, the research on CZTS/TiO2 is still in its infancy and the performances reported in the literature are generally very poor.

The researchers of the Department of Materials Science and of the MIB-SOLAR center of the University of Milano-Bicocca, in a study led by Dr. Giorgio Tseberlidis, Dr. Valerio Di Palma, and Prof. Simona Binetti, managed to produce an efficient and eco-friendly kesterite solar cell, in collaboration with a research group of ENEA (Rome). TiO2 thin films were obtained through O2-plasma Atomic Layer Deposition and the final solar devices showed the latest record efficiency for CZTS/TiO2 heterojunction in standard configuration with η = 3.01%, Jsc of ~16 mA/cm2 and Voc ~460 mV, comparable with the CZTS/CdS reference devices (η ~ 4%) of the same team.

The results of the study are reported in the paper “Titania as Buffer Layer for Cd-Free Kesterite Solar Cells" (DOI: 10.1021/acsmaterialslett.2c00933) published on ACS Materials Letters (Impact Factor 11.170, Journal Citation Report (Clarivate Analytics, 2021)).