Although research on lead halide perovskites has skyrocketed during the past two decades, the quest for lead-free alternatives has led to the emergence of chalcogenide perovskites (CPs) as optoelectronic materials. Within the CP class, BaZrS₃ stands out as having a highly stable perovskite structure comprised of naturally abundant elements and better environmental compatibility with potential for large-scale manufacturing. Furthermore, BaZrS₃ has a direct bandgap of 1.7 – 1.9 eV and its absorption coefficient reaches 10⁵ cm^-1, characteristics suitable for a large generation of electron-hole pairs upon illumination in a PV tandem device. However, device development is at an early stage, with efforts focusing primarily on the optimization of the BaZrS₃ processing conditions. To advance in device designing, it is crucial to understand the charge transfer mechanisms occurring at the interfaces by the investigation of the band alignment and the band matching with other materials. An effective way of achieving surface and interface knowledge is through utilizing photoelectron spectroscopy (PES).

In this presentation, we will report our advances in the understanding of the novel material BaZrS₃, a potential candidate for a new generation of photovoltaic devices. The investigation of the samples combined both bulk analyses (XAS, XRD, PL, EDX) and surface techniques (PES, with soft and hard X-rays). The BaZrS₃ thin films synthesized at different annealing temperatures were investigated in terms of temperature-evolution of local geometry around the Zr atoms, improved crystallinity, crystallite growth and photoluminescence signal [1,2]. A correlation of these techniques allowed us to get a detailed knowledge of structural and functional properties (Fig 1(a)). The surface analysis was employed for understanding the interfaces, essential for device integration. With soft and hard X-ray PES [3], we could probe into several nm from the surface, which revealed a structured surface. Furthermore, we compared our electronic measurements to DFT calculations (Fig 1(b)), showing a good agreement, and we could experimentally evaluate the valence band maximum, useful for functional applications. The comprehension of the material’s properties is key for its advance towards the device fabrication, and towards the design of devices as efficient as the lead perovskite-based solar cells.