Spin-coating processing of an oriented Sb2S3 layer for PV applications: effect of the precursors and device architecture

Abstract

Sb₂S₃ stands out as a low-toxicity, promising material for photovoltaic applications because of its unique optoelectronic properties such as a suitable band gap (1.4–1.8 eV), a high absorption coefficient (10⁵ cm⁻¹), appreciable thermal and chemical stability, and a high tolerance to defects. In the first part of this study, Sb(Ac)₃ and SbCl₃ are compared as antimony precursors for the formation of the Sb₂S₃ photoactive film. The Sb(Ac)₃/thiourea (TU) precursor solution allows the formation of films with higher coverage and uniformity compared to films obtained from SbCl₃/TU. In terms of PV efficiencies, Sb(Ac)₃/TU and SbCl₃/TU based layers respectively lead to 4.9% and 4.8% efficiencies. Indeed, the band gap of the Sb₂S₃ layer obtained from Sb(Ac)₃/TU (1.75 eV) is less favorable than that from SbCl₃/TU (1.65 eV). In addition, the [hk1] crystalline orientation of Sb₂S₃ is more favorable for efficient charge transfer in the devices and is more prevalent in the SbCl₃/TU films. In the second part, the incorporation of a mesoporous TiO₂ network is considered to improve charge transport at the Sb₂S₃/TiO₂ electron transport layer interface and hence enhance the efficiency of the devices. However, the PV efficiencies are significantly lower in the case of the mesoporous architecture, which is mainly attributed to a [hk0] misorientation of the crystals in the mesoporous architecture leading to poor charge transfer. By studying the impact of the antimony precursor and the nature of the TiO₂ electron transport underlayer (dense or mesoporous) on the properties of the Sb₂S₃ photoactive film, we highlight that a combination of three factors is crucial to boost device efficiencies: uniformity/coverage, adequate bandgap, and more importantly crystalline orientation.