Air Stable, High‐Efficiency, Pt‐Based Halide Perovskite Solar Cells with Long Carrier Lifetimes

Abstract

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.

Ultralow Lattice Thermal Conductivity in Double Perovskite Cs2PtI6: A Promising Thermoelectric Material

“…When taking spin−orbit coupling (SOC) into account, the triple degenerated bands at the valence band maxima split with 0.08 eV, the valence band becomes more dispersive along the Γ−X direction, and the band gap reduces by 0.18 eV. The reported band gap, with HSE (HSE-SOC), of 1.40 eV (1.22 eV) agrees well with the experimental value of 1.40 eV 15 and is appropriate for solar cells operating near the visible region of the light spectrum. As can be seen from the density of states (DOSs) in Figure 2, the valence band has its main contribution from the I p states, followed by a small contribution from the Pt d states.…”

“…The Cs atoms are situated at the 8c Wyckoff positions and (0.25, 0.25, 0.25) coordinates, Pt atoms at 4a Wyckoff positions and (0, 0, 0) coordinates, and I atoms at 24e Wyckoff positions and (x, 0, 0) coordinates, where x value is around 0.20. 25 The optimized lattice constant is listed in Table 1, including the comparison with the previously reported theoretical 7 and experimental 15 values. We have found Cs 2 PtI 6 to be an indirect band gap material, as can be seen from the calculated band structure in Figure 2, considering the high symmetry points Γ(0, 0, 0), X(0.5, 0, 0.5), U(0.625, 0.25, 0.625), K(0.375, 0.375, 0.75), L(0.5, 0.5, 0.5), and W(0.5, 0.25, 0.75).…”

“…14 Very recently, airstable and high-quality Cs 2 PtI 6 was synthesized in the cubic phase (space group Fm3̅ m) by atmospheric solution processing, and it was shown to have excellent absorption coefficient (4 × 10 5 cm −1 ), high hole mobility (62.6 cm 2 /(V s)), and high minority carrier lifetimes (>2 μs). 15 The potential application of Cs 2 PtI 6 in thermoelectrics is yet to be explored as neither experimental nor theoretical investigation exists. Since the DFT, combined with the semiclassical Boltzmann transport theory, has been successfully employed in predicting thermal transport for a wide variety of materials, 16−18 we have conducted a comprehensive study to probe the thermoelectric properties of Cs 2 PtI 6 by taking into account both electronic and phonon contributions.…”

“…In particular, its nontoxic nature is advantageous compared to, for example, the organic CH 3 NH 3 PbX 3 (X = Cl, Br, and I) halides in photovoltaics and inorganic Bi 2 Te 3 in thermoelectric . Very recently, air-stable and high-quality Cs 2 PtI 6 was synthesized in the cubic phase (space group Fm 3̅ m ) by atmospheric solution processing, and it was shown to have excellent absorption coefficient (4 × 10 5 cm –1 ), high hole mobility (62.6 cm 2 /(V s)), and high minority carrier lifetimes (>2 μs) . The potential application of Cs 2 PtI 6 in thermoelectrics is yet to be explored as neither experimental nor theoretical investigation exists.…”

Additive-Assisted Optimization in Morphology and Optoelectronic Properties of Inorganic Mixed Sn-Pb Halide Perovskites

“…The procedure and instruments for films fabrication and testing follow our previous work, reported by Schwartz et al [ 40 ]. Perovskite films were fabricated via precursor-based solution processing under the atmospheric condition, as demonstrated in Figure 1 .…”