High-Bandgap Perovskite Materials for Multijunction Solar Cells

High-bandgap (>1.7 eV) mixed halide perovskites for multijunction solar cells are usually affected by photoinduced phase segregation, which triggers subbandgap defects that are detrimental to the open-circuit voltage. While this effect may be reversed, e.g., when leaving the cells in the dark, new perovskite compositions that exhibit enhanced stability may be required. In this Perspective, the compositional space beyond the conventional methylammonium-and formamidinium-based mixed halide compounds is reviewed in light of multijunction applications. These alternative absorber compositions include: (1) layered or quasi-2D perovskites, where larger organic cations are incorporated into the structure; (2) inorganic perovskites (i.e., when the organic components are removed altogether); and (3) lead-free structures, where the toxic lead is substituted by one or more elements. The development perspectives of high-efficiency and stable perovskite materials based on these compositions are discussed in view of an integration in multijunction solar cells.