Mixed Pt-Ni Halide Perovskites for Photovoltaic Application.

CsPtI 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(PtNi)(I,Cl) thin films on the properties and stability of the perovskite material. Films fabricated with CsI and PtI precursors result in a perovskite phase with a bandgap of 2.13 eV which transitions into stable CsPtI with a bandgap of 1.6 eV upon annealing. The complete substitution of PtI in films with CsI + NiCl precursors results in a wider bandgap of 2.35 eV and SEM shows two phases-a rod-like structure identified as CsNi(I,Cl) 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 CsNiCl with a peak shift to higher 2-theta. The partial substitution of PtI with NiCl in mixed 50-50 Pt-Ni-based films produces a bandgap of 1.9 eV, exhibiting a phase of Cs(Pt,Ni)(I,Cl) 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.