Semiconductor to metallic transition under induced pressure in Cs2AgBiBr6 double halide perovskite: a theoretical DFT study for photovoltaic and optoelectronic applications

Effective bandgap narrowing and enhanced optoelectronic performance of Cs2PtBr6 double perovskites by pressure engineering

Tuning the structure-property relations of perovskites by pressure engineering holds great promise for discovering materials with favorable properties. The newly synthesized Cs2PtBr6 double perovskite exhibits excellent water resistance and chemical stability. Yet its photoelectric conversion efficiency is limited by its intrinsic wide-bandgap nature. In this work, based on density functional theory calculations, we demonstrate the bandgap narrowing of Cs2PtBr6 via pressure engineering and maintain its structural stability. Strikingly, upon applying pressure up to 12 GPa, the bandgap value decreases to 1.34 eV, which exactly reaches the optimal bandgap required by the Shockley-Queisser efficiency limit. Moreover, optical calculation analysis shows that the optical absorption of Cs2PtBr6 exhibits a significant improvement within the visible range. Therefore, the potential of Cs2PtBr6 as a photovoltaic material by pressure engineering is improved. This work is useful for designing and synthesizing new perovskite materials with enhanced performance.

First-principles study on structural, electronic and optical properties of halide double perovskite Cs2AgBX6 (B = In, Sb; X = F, Cl, Br, I)

All-inorganic halide double perovskites (HDPs) attract significant attention in the field of perovskite solar cells (PSCs) and light-emitting diodes. In this work, we present a first-principles study on structural, elastic, electronic and optical properties of all-inorganic HDPs Cs₂AgBX₆ (B = In, Sb; X = F, Cl, Br, I), aiming at finding the possibility of using them as photoabsorbers for PSCs. Confirming that the cubic perovskite structure can be formed safely thanks to the proper geometric factors, we find that the lattice constants are gradually increased on increasing the atomic number of the halogen atom from F to I, indicating the weakening of Ag-X and B-X interactions. Our calculations reveal that all the perovskite compounds are mechanically stable due to their elastic constants satisfying the stability criteria, whereas only the Cl-based compounds are dynamically stable in the cubic phase by observing their phonon dispersions without soft modes. The electronic band structures are calculated with the Heyd-Scuseria-Ernzerhof hybrid functional, demonstrating that the In (Sb)-based HDPs show direct (indirect) transition of electrons and the band gaps are decreased from 4.94 to 0.06 eV on going from X = F to I. Finally, we investigate the macroscopic dielectric functions, photo-absorption coefficients, reflectivity and exciton properties, predicting that the exciton binding strength becomes weaker on going from F to I.

Phase stability and electronic structure of CsPbCl3 under hydrostatic stress and anion substitution

Perovskites based on CsPbX₃ (X = Cl, Br, I) have promising applications in solar cells, light-emitting diodes, and photodetectors. In this paper, the phase stability of inorganic metal halide perovskite CsPbCl₃ under hydrostatic pressure and anion substitution is studied using density functional theory (DFT), and this modification is explained by the interaction of the octahedrons and transformation of the bond-orbital coupling. In addition, two space groups, P4/mbm and Amm2, which are stable under stress, are subjected to anion substitution; then, the structural stability and band gap change of CsPbCl_3-yX_y (X = Br, I; y = 0, 1, 2, 3) are analyzed after applying stress; finally, the electronic structures and optical properties of the six most stable components are presented. The effect of stress and anions on the components' optoelectronic properties is closely linked with the crystal's structural alteration mechanism. These results show that stress and anion modulation can significantly change the optoelectronic properties of materials, which make these materials have broad application prospects. Furthermore, stress can be used as an effective tool for screening the most stable material structure.

Thermochromic Cs2 AgBiBr6 Single Crystal with Decreased Band Gap through Order-Disorder Transition

Lead-free Cs₂ AgBiBr₆ double perovskite is considered to be a promising alternative to the traditional lead-based analogues due to its long carrier lifetime, high structural stability, and non-toxicity. However, the large band gap limits its absorption of visible light, which is not conducive to further optoelectronic applications. Herein, a thermochromic strategy is reported to decrease the band gap of Cs₂ AgBiBr₆ by approximately 0.36 eV, obtaining the smallest reported band gap of 1.69 eV under ambient conditions. The experimental data indicate that after annealing the Cs₂ AgBiBr₆ single crystals at 400 °C, the silver (Ag) and bismuth (Bi) atoms occupy the B-site in a random way and form a partially disordered configuration. The formation of the antisite defects broadens the band edges and decreases the band gap. This work offers new insights into the preparation of narrow band gap lead-free double perovskites, and a deep understanding of their structural and electronic properties for further development in photoelectric devices.

Air processed Cs2AgBiBr6 lead-free double perovskite high-mobility thin-film field-effect transistors

This study focuses on the fabrication and characterization of Cs₂AgBiBr₆ double perovskite thin film for field-effect transistor (FET) applications. The Cs₂AgBiBr₆ thin films were fabricated using a solution process technique and the observed XRD patterns demonstrate no diffraction peaks of secondary phases, which confirm the phase-pure crystalline nature. The average grain sizes of the spin-deposited film were also calculated by analysing the statistics of grain size in the SEM image and was found to be around 412 (± 44) nm, and larger grain size was also confirmed by the XRD measurements. FETs with different channel lengths of Cs₂AgBiBr₆ thin films were fabricated, under ambient conditions, on heavily doped p-type Si substrate with a 300 nm thermally grown SiO₂ dielectric. The fabricated Cs₂AgBiBr₆ FETs showed a p-type nature with a positive threshold voltage. The on-current, threshold voltage and hole-mobility of the FETs decreased with increasing channel length. A high average hole mobility of 0.29 cm² s⁻¹ V⁻¹ was obtained for the FETs with a channel length of 30 µm, and the hole-mobility was reduced by an order of magnitude (0.012 cm² s⁻¹ V⁻¹) when the channel length was doubled. The on-current and hole-mobility of Cs₂AgBiBr₆ FETs followed a power fit, which confirmed the dominance of channel length in electrostatic gating in Cs₂AgBiBr₆ FETs. A very high-hole mobility observed in FET could be attributed to the much larger grain size of the Cs₂AgBiBr₆ film made in this work.

The effect of metal substitution in CsSnI3 perovskites with enhanced optoelectronic and photovoltaic properties

Non-toxic lead-free halide metal perovskites have gained significant interest in photovoltaic and optoelectronic device applications. In this manuscript, we have studied the structural, electronic, mechanical, and optical properties of eco-friendly cubic CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) perovskites applying first-principles pseudopotential-based density functional theory (DFT). Cu-doped CsSnI₃ has a large impact on the band gap energy viz. the transition of direct band gap towards the indirect band gap. The mechanical properties demonstrate that the pristine and Cu-doped CsSnI₃ samples are mechanically stable and their ductility is enhanced by Cu doping. The mechanical stability and ductility favors the suitability of pure and Cu-doped samples in the thin film industry. The absorption edge of Cu-doped CsSnI₃ moves towards the lower energy region in comparison with their pure form. In addition, the high dielectric constant, high optical absorption, and high optical conductivity of Cu-doped CsSnI₃ materials suggests that the studied materials have a broad range of applications in optoelectronic devices, especially solar cells. A combined analysis of the structural, electronic, mechanical and optical properties suggests that CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) samples are a suitable candidate for photovoltaic as well as optoelectronic device applications.