Energies (May 2023)

Effect of the ZnSnO/AZO Interface on the Charge Extraction in Cd-Free Kesterite Solar Cells

  • Carla Gobbo,
  • Valerio Di Palma,
  • Vanira Trifiletti,
  • Claudia Malerba,
  • Matteo Valentini,
  • Ilaria Matacena,
  • Santolo Daliento,
  • Simona Binetti,
  • Maurizio Acciarri,
  • Giorgio Tseberlidis

DOI
https://doi.org/10.3390/en16104137
Journal volume & issue
Vol. 16, no. 10
p. 4137

Abstract

Read online

Cu2ZnSnS4 (CZTS) is a promising absorber material to produce thin film solar cells thanks to its high absorption coefficient, low cost and low toxicity. CdS is commonly used as a buffer layer for CZTS solar cells but, beyond its toxicity, it has a nonoptimal band alignment with CZTS. ZnxSn1−xO (ZTO), based on earth-abundant and nontoxic elements and with a large and tunable band gap, is a suitable alternative buffer layer. In this paper, the atomic layer deposition (ALD) of ZTO was employed by testing different compositions and thicknesses. ALD not only leads to very compact and homogenous ZTO layers (enabling tuning the stoichiometry of the ZTO so prepared) but also makes the i-ZnO layer (usually sandwiched between the buffer layer and the transparent contact) redundant and detrimental. Through SCAPS simulation and impedance measurements, the ZnSnO/AZO interface impact on the Cd-free kesterite solar cells’ performances has been investigated, highlighting its leading role in achieving an effective charge extraction and the detrimental effect of the i-ZnO layer. With this approach, a solar cell based on an architecture simpler and more eco-friendly than the conventional one has been produced with comparable efficiencies.

Keywords