Lead halide perovskites (LHPs), have attracted considerable attention across various applications owing to their exceptional optoelectronic properties. However, the main challenge hindering the broad adoption of lead halide perovskites lies in their stability and toxicity. In this review, we summarize the outstanding properties of platinum (Pt) halide perovskites, with a particular focus on the stability and applications of Cs₂PtI₆ and its derivatives. Cs₂PtI₆ has shown promising efficiency for photovoltaic devices, as well as photoelectrochemical water splitting with stable behavior in acid or basic conditions. Cs₂PtI₆ also shows promise in gas sensing and thermoelectric devices. The emergence of 2D Pt (II) halide perovskites opens up new avenues for environmentally friendly materials for photonic and optoelectronic devices like room temperature phosphoresce and triplet‐triplet annihilation (TTA) based up‐conversion. image

Solar-driven hydrogen generation is one of the promising technologies developed to address the world’s growing energy demand in an sustainable way. While, for hydrogen generation (otherwise water splitting), photocatalytic, photoelectrochemical, and PV-integrated water splitting systems employing conventional semiconductor oxides materials and their electrodes have been under investigation for over a decade, lead (Pb)- halide perovskites (HPs) made their debut in 2016. Since then, the exceptional characteristics of these materials, such as their tunable optoelectronic properties, ease of processing, high absorption coefficients, and long diffusion lengths, have positioned them as a highly promising material for solar-driven water splitting. Like in solar photovoltaics, a solar-driven water splitting field is also dominated by Pb-HPs with ongoing efforts to improve material stability and hydrogen evolution/generation rate (HER). Despite this, with the unveiling potential of various Pb-free HP compositions in photovoltaics and optoelectronics researchers were inspired to explore the potential of these materials in water splitting. In this current review, we outlined the fundamentals of water splitting, provided a summary of Pb HPs in this field, and the associated issues are presented. Subsequently, Pb-free HP compositions and strategies employed for improving the photocatalytic and/or electrochemical activity of the material are discussed in detail. Finally, this review presents existing issues and the future potential of lead-free HPs, which show potential for enhancing productivity of solar-to-hydrogen conversion technologies.

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.

Platinum-based halide perovskites exhibit promising optoelectronic properties along with merits of low-temperature processing and stability. Current research on Pt halide perovskites is limited to 0D A2BX6 structure as the ABX3 3D structure is thermodynamically unstable. Herein, we report the stabilization of the ABX3 structure into a 2D layered phase, CsPtI3(DMSO), that is stable up to 181.5 C. The 2D phase shows an excitonic peak at the absorption edge of 600 nm, indicating quantum confinement. It also exhibits a large Stokes shift due to intersystem crossing (ISC), with a quenched singlet excitonic fluorescence at 610 nm and strong triplet emission at 852 nm. Pt(II) co-ordinates with dimethyl sulfoxide (DMSO) via -donation of S lone-pair electrons and - back donation from Pt to S, stabilizing CsPtI3(DMSO) layered structure. The strong electronic interaction between DMSO and Pt(II) and orbital mixing lead to spin-orbit-coupling, facilitating ISC and singlet-to-triplet exciton energy transfer. The interaction of Pt and DMSO is further confirmed by addition of thioacetamide (TAA), a strong S-donor, which retards the formation of 2D layered structure, and directly results in Cs2PtI6 and Pt.

Platinum halide perovskites offer an environmentally friendly alternative to lead halide perovskites, demonstrating remarkable stability and optoelectronic properties. Here, the impact of dimensional engineering on optoelectronic properties of platinum halide perovskites, specifically 2D and 0D , has been explored. The 2D phase shows p‐type behavior and exhibits significant Stokes shift with broad emission around 850 nm. Strong short‐range electron–phonon (EP) coupling in the layered 2D structure results in self‐trapped excitonic emission as confirmed by low emission lifetime and Huang–Rhys factor of S = 16.8. In contrast, in this study, 0D exhibits n‐type behavior and no significant emissions under laser excitation, attributed to short‐range EP coupling leading to nonradiative recombination. Additionally, the mixed phase resulting from thermal decomposition of 2D behaves as a p‐type semiconductor. This observation aligns with first principles simulations, which suggest that low formation energy Pt interstitial defects in will tune the pristine n‐type into a slightly p‐type conductivity. These findings underscore the profound influence of dimensional engineering on the properties of platinum halide perovskites, offering valuable insights for developing stable and environmentally friendly perovskite materials for advanced optoelectronic applications.