Halide perovskite materials are recognized as being the most promising absorber layers for tandem solar cell applications. Silicon/Perovskite tandem devices (Si/PK) are undergoing a revolution the last decade with a power conversion efficiency that surpasses the 35%. However, create a stable, reliable and attractive PV market for this type of devices remain challenging. The main issues to address in Si/PK research field are the upscaling process for the PK material deposition on textured Si wafers and the intrinsic and extrinsic stability of the tandem device.

The key features of a PK deposition process in order to consider the fabrication technique a good candidate for upscaling, are the PK good uniformity and coverage of the textured Si surface, the high deposition rate and the low power and material consumption. Based on these criteria in this talk we will first discuss the strengths and weaknesses of the main deposition categories: i) the wet processes (slot-die, Dr blade, ink jet …), ii) the fully vapor-based techniques (co-evaporation, close space sublimation …) and iii) hybrid processes (dry vapor process followed by wet coating).

We will focus on the close space sublimation (CSS) and the co-sublimation (usually called co-evaporation in the literature) techniques for the deposition of the inorganic precursors used in the two-step processes where the inorganic scaffold is deposited first and then it is converted into a perovskite during a second organic-based deposition step followed by an annealing. The two-step processes studied in our work are the hybrid process and the two-step (sequential) full-vapor process. The majority of the published articles on the vapor-based or the hybrid techniques use the co-sublimation process for the deposition of the inorganic scaffold. Hence very little is known about the CSS technique and its impact on the growth mechanism, the chemical and physical properties of the inorganic scaffold.

In these talk, we will compare the physical properties of the inorganic scaffold deposited by CSS and co-sublimation and we will discuss the critical points that influence the morphology, the crystalline structure and the homogeneity of the inorganic thin film. Our preliminary studies indicate that the choice of halogens, the substrate temperature and the composition of the CSS source has an important impact on the thermodynamic and kinetic properties of the deposited film and consequently on the morphology and crystalline structure of the inorganic scaffold. As a result, in the case of the two-step processes such as the hybrid process or the sequential full vapor process, the overall process duration, the crystalline quality, the physical and chemical properties of the final PK layer are highly influenced by the first inorganic step.

Finally we integrate the PK thin film Si/PK tandem device of 9 cm² active area using three different deposition techniques for the PK material: (i) the full wet PK deposition process on chemically polished and nano-textured Si wafer, (ii) hybrid process and (iii) two-step full vapor process using co-sublimation and CSS deposition on fully textured Si wafer. We compare the photovoltaic parameters and the stability of tandem devices and we discuss the main challenges to overcome in order to address the main stability issues and upscale drawbacks in the case of fully textured Si/PK tandem solar cells.