Close space sublimation of perovskite materials for PV applications

Tandem perovskite-silicon solar cells have attracted tremendous attention due to their performances with certified efficiencies above 34% at laboratory scale. These outstanding performances have been achieved using solution-based processes, which may be a hint towards industrialization, because of the inherent limitations of the liquid processes (solution waste management, scalability and conformal deposition on textured Si bottom cells).To overcome these issues, vacuum based processes have been developed recently, such as co-evaporation or Close Space Sublimation (CSS). The CSS designation is however used in literature for very different processes with only the common feature of a short source-to-substrate distance. This designation actually covers:- CSS deposition: a method to deposit material from a single source material (eg. CsPbBr3)- CSS impregnation: a method to impregnate inorganic material with an organic compound (eg. using FAI to transform PbI2 to FAPbI3).Both approaches are relevant for PV applications and can be used depending on the material to be synthesized. In this contribution we explore the potentiality of the CSS technique to fabricate perovskite-silicon tandem cells, using:- CSS deposition of inorganic perovskite materials (CsPb(I,Br)3) have been explored as absorbers for tandem devices.- CSS deposition of inorganic precursors (CsBr + PbI2) has been used as a first stage for the synthesis of hybrid CsFAPb(I,Br)3 photovoltaic absorbers- CSS impregnation of inorganic precursors with FAI and FABr for the synthesis of hybrid CsFAPb(I,Br)3 photovoltaic absorbersThis contribution will focus on the potential, advantages and drawbacks of the CSS synthesis method (both deposition and impregnation strategies) for PV absorbers deposition with a particular attention paid on the physical mechanism underlying the CSS deposition process. Understanding the CSS deposition method is a prerequisite to determine the applicability of such a method and to be able to optimize device performances. This demonstration will be supported by solar cells fabrication and performances analysis.