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The search for Pb-free perovskite materials continues with limited success to find a suitable replacement for Pb with outstanding optoelectronic properties. Here we report Pb-free inorganic halide perovskite Cs 2 PtI 6 with excellent absorption coefficient, long minority carrier lifetime and optical bandgap of 1.4 eV. Atmospheric precursor based solution processing results in high quality Cs 2 PtI 6 with absorption coefficient of 4 10 � �� for photon energies > 1.5 eV and high minority carrier lifetimes of > 2 s indicating low defect density in the material. Superstrate n-i-p solar cells processed with the structure F:SnO 2 /CdS/Cs 2 PtI 6 /carbon/Cu show promising device efficiency of 13.88%. These planar devices processed under atmospheric conditions show low V oc deficit (< 0.3 V) without any hysteresis in forward and reverse scans indicating low trap densities. Pt offers an excellent model system for replacement of Pb due to high atomic number, oxidation resistance and stability. Cs 2 PtI 6 is an atmospherically stable phase under AM1.5G and 65 C upto 1000 hours.Organic-inorganic hybrid halide perovskite solar cells (HPSCs) have attracted immense attention because of excellent optoelectronic properties and record power conversion efficiency (PCE) has reached 25.2% from 3.8% within a few years. [1][2][3][4][5][6] Despite the very high efficiency already attained by HPSCs (ABX 3 ; A = MA, FA, Cs; B = Pb, Sn; X=I, Br, Cl) resulting from high absorption coefficient and electron-hole diffusion lengths; toxicity of Pb and stability of these materials are veritable issues. Replacing MA + and FA + with PEA + , BA + , Cs + has shown to enhance the stability of hybrid perovskite solar cells against thermal and moisture related degradation. [7][8][9][10][11] The superior optoelectronic properties of Pb-based halide perovskites are attributed to the inactive Pb 6s orbitals, and can be replaced by Ge 2+ , Sn 2+ , Sb 3+ , Bi 3+ , Cu 2+ with inactive s orbitals. Replacement of Pb 2+with Sn 2+ and Ge 2+ seems to be a logical solution for addressing the toxicity issues and results in excellent optoelectronic properties such as high absorption coefficient, high hole mobility resulting Accepted Article replacement for Pb with outstanding optoelectronic properties.

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Optoelectronic properties of organic-inorganic halide perovskites are exceptional with solar cells showing efficiency comparable with conventional photovoltaic technologies. However, with issues of material stability and toxicity of Pb, it is important to understand if Pb can be replaced while maintaining the high power conversion efficiencies of (FA,MA,Cs)Pb(I,Br) 3. Herein, practical efficiency limits of Pb and Pb-free perovskite absorbers are analyzed using a 1D simulator for n-i-p or p-in device structures. SCAPS-1D baseline models for perovskite absorber materials with and without Pb are developed to numerically reproduce the experimental current density-voltage (JV) and external quantum efficiency (EQE) of champion devices from literature. From these baseline models, the efficiency limits are determined based on optimizing the interface band alignments, reduction in midgap defect density, increased absorption coefficient, and no parasitic losses. SCAPS-1D simulations suggest that 1) theoretically determined efficiency limit of Cs 2 PtI 6 perovskites is comparable with (FA,MA,Cs)Pb(I,Br) 3 perovskites, 2) FA 4 GeSbCl 12 is a promising photoabsorber; and 3) for efficient photoconversion with Sn-, Ge-, Ti-, or Ag-based compounds, a reduction of defect density and increase in absorption coefficient is needed.