Cs₂PtI₆ is a promising photoabsorber with a direct bandgap of 1.4 eV and a high carrier lifetime; however, the cost of Pt inhibits its commercial viability. Here, we performed a cost analysis and experimentally explored the effect of replacing Pt with earth-abundant Ni in solution-processed Cs(Pt_xNi_1−x)(I,Cl)₃ thin films on the properties and stability of the perovskite material. Films fabricated with CsI and PtI₂ precursors result in a perovskite phase with a bandgap of 2.13 eV which transitions into stable Cs₂PtI₆ with a bandgap of 1.6 eV upon annealing. The complete substitution of PtI₂ in films with CsI + NiCl₂ precursors results in a wider bandgap of 2.35 eV and SEM shows two phases—a rod-like structure identified as CsNi(I,Cl)₃ and residual white particles of CsI, also confirmed by XRD and Raman spectra. Upon extended thermal annealing, the bandgap reduces to 1.65 eV and transforms to CsNiCl₃ with a peak shift to higher 2-theta. The partial substitution of PtI₂ with NiCl₂ in mixed 50-50 Pt-Ni-based films produces a bandgap of 1.9 eV, exhibiting a phase of Cs(Pt,Ni)(I,Cl)₃ composition. A similar bandgap of 1.85 eV and the same diffraction pattern with improved crystallinity is observed after 100 h of annealing, confirming the formation of a stable mixed Pt-Ni phase.

Cs2PtI6 is a promising photoabsorber with direct bandgap of 1.4 eV and high carrier lifetime, however, the cost of Pt inhibits its commercial viability. Here, we explore the effect of replacing Pt with earth-abundant Ni in solution-processed Cs(PtxNi1-x)(I,Cl)3 thin-films on the properties and stability of the perovskite material. Films fabricated with CsI and PtI2 precursors result in perovskite phase with bandgap of 2.13 eV which transitions into stable Cs2PtI6 with a bandgap of 1.6 eV upon annealing. Complete substitution of PtI2 in films with CsI + NiCl2 precursors results in a wider bandgap of 2.35 eV and SEM shows 2 phases- a rod-like structure identified as CsNi(I,Cl)3 and residual white particles of CsI, also confirmed by XRD and Raman spectrum. Upon extended thermal annealing, the bandgap reduces to 1.65 eV and transforms to CsNiCl3 with a peak shift to higher 2-theta. Partial substitution of PtI2 with NiCl2 in mixed 50-50 Pt-Ni-based films produces a bandgap of 1.9 eV exhibiting a phase of Cs(Pt,Ni)(I,Cl)3 composition. A similar bandgap of 1.85 eV and the same diffraction pattern with improved crystallinity is observed after 100 hours of annealing, confirming the formation of a stable mixed Pt-Ni phase.