Fabrication of Cd-free In2S3/Cu3SnS4 Heterojunction Thin Film Solar Cells


Akçay N., Buskıs K. P., Özen Y., Gremenok V. F., Zaretskaya E. P., Özçelik S.

See Future PV Latsis Symposium on Earth-Abundant Materials for Future Photovoltaics (EPFL), Lausanne, Switzerland, 22 - 24 June 2022, pp.105-106

  • Publication Type: Conference Paper / Summary Text
  • City: Lausanne
  • Country: Switzerland
  • Page Numbers: pp.105-106
  • Gazi University Affiliated: Yes

Abstract

In recent years, I-IV-VI ternary semiconductor compound Cu2SnS3 (CTS), which is composed of earth-abundant and nontoxic elements, has been intensively studied by the researchers as a promising absorber material owing to its suitable optoelectronic properties such as direct band gap ranging from 0.8 eV to 1.7 eV, high optical absorption coefficient in the order of 104 cm-1 and p-type conductivity [1]. The record efficiency value reported for CTS-based solar cells that have CdS buffer layer and pure CTS absorber is ~4.3% up to now [2]. This value is still so far from Schockley-Queisser efficiency limit of ~30% estimated for a single junction solar cell based on CTS [3]. Here, we present the studies on the growth of Cu3SnS4 thin film absorbers by a two-step approach including the deposition of precursor stacks and subsequently their sulfurization, and the development of thin film solar cells with In2S3 buffer layer. At first, we show the effect of sulfurization time on the structural and morphological properties of the films by using X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy and secondary ion mass spectroscopy (SIMS) techniques in detail. We discuss on the co-existence of different structural polymorphs of CTS and the phase transformation from CTS to Cu3SnS4 depending on sulfurization time by considering both the findings in previously reported studies and our study and the discrepancies in the literature. Then, we report an efficiency value of ~3% obtained from a solar cell device that have Cu3SnS4 absorber and In2S3 buffer layers and indicate a slight increase in the efficiency over a thermal annealing process of the device. To the best of our knowledge, only one study was reported on the photovoltaic behaviour of Cu-rich films among the members of Cu-Sn-S family up to now [4]. In that study, an efficiency value of 2.34% was obtained from a solar cell structure of Mo/Cu4SnS4/In2S3/TiO2/FTO glass. In this context, we report photovoltaic property of Cu3SnS4 absorber in a In2S3/Cu3SnS4 heterojunction structure for the first-time. Furthermore, we show that diffusion of In element from the In2S3 buffer layer into the absorber occurs up to a certain depth independent of the thermal annealing process of the solar cells by SIMS analysis. We think that this might be leaded to the partial substitution of In atoms by Sn atoms in the crystal structure. However, more detailed studies are needed to fully understand it.