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Abstract 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 Cs₂PtI₆and its derivatives. Cs₂PtI₆has shown promising efficiency for photovoltaic devices, as well as photoelectrochemical water splitting with stable behavior in acid or basic conditions. Cs₂PtI₆also 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. 

Halide perovskite solar cells (HPSCs) are promising photovoltaic materials due to their excellent optoelectronic properties, low cost, and high efficiency. Here, we demonstrate atmospheric solution processing and stability of cesium tin-lead triiodide (CsSnPbI3) thin films for solar cell applications. The effect of additives, such as pyrazine and guanidinium thiocyanate (GuaSCN), on bandgap, film morphology, structure, and stability is investigated. Our results indicate the formation of a wide bandgap (>2 eV) structure with a mixed phase of tin oxide (SnO2) and Cs(Sn, Pb)I3. The addition of pyrazine decreases the intensity of SnO2 peaks, but the bandgap does not change much. With the addition of GuaSCN, the bandgap of the films reduces to 1.5 eV, and a dendritic structure of Cs(Sn, Pb)I3 is observed. GuaSCN addition also reduces the oxygen content in the films. To enable uniform film crystallization, cesium chloride (CsCl) and dimethyl sulfoxide (DMSO) additives are used in the precursor. Both CsCl and DMSO suppress dendrite formation with the latter resulting in uniform polycrystalline films with a bandgap of 1.5 eV. Heat and light soaking (HLS) stability tests at 65 °C and 1 sun for 100 h show all film types are stable with temperature but result in phase segregation with light exposure. 

Abstract 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 A₂BX₆structure as the ABX₃3D structure is thermodynamically unstable. Herein, the study reports the stabilization of the ABX₃structure 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 σ‐donation of S lone‐pair electrons and π‐ 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 Cs₂PtI₆and Pt. 

Air‐stable p‐type SnF₂:Cs₂SnI₆with a bandgap of 1.6 eV has been demonstrated as a promising material for Pb‐free halide perovskite solar cells. Crystalline Cs₂SnI₆phase is obtained with CsI, SnI₂, and SnF₂salts in gamma‐butyrolactone solvent, but not with dimethyl sulfoxide andN,N‐dimethylformamide solvents. Cs₂SnI₆is found to be stable for at least 1000 h at 100 °C when dark annealed in nitrogen atmosphere. In this study, Cs₂SnI₆has been used in a superstrate n–i–p planar device structure enabled by a spin‐coated absorber thickness of ≈2 μm on a chemical bath deposited Zn(O,S) electron transport layer. The best device power conversion efficiency reported here is 5.18% withV_OCof 0.81 V, 9.28 mA cm⁻²J_SC, and 68% fill factor. The dark saturation current and diode ideality factor are estimated as 1.5 × 10⁻³ mA cm⁻²and 2.18, respectively. The devices exhibit a highV_OCdeficit and low short‐circuit current density due to high bulk and interface recombination. Device efficiency can be expected to increase with improvement in material and interface quality, charge transport, and device engineering.