Project description:Structure and properties of an inorganic perovskite Cs2SnI6 demonstrated its potential as a light-harvester or electron-hole transport material; however, its optoelectronic properties are poorer than those of lead-based perovskites. Here, we report the way of light tuning of absorption and transport properties of cesium iodostannate(IV) Cs2SnI6 via partial heterovalent substitution of tin for indium. Light absorption and optical bandgaps of materials have been investigated by UV-vis absorption and photoluminescent spectroscopies. Low-temperature electron paramagnetic resonance spectroscopy was used to study the kind of paramagnetic centers in materials.
Project description:In the present study, the structural, mechanical, electronic and optical properties of all-inorganic vacancy-ordered double perovskites A2Sn1-xTixY6 (A = K, Rb, Cs; Y = Cl, Br, I) are explored by density functional theory. The structural and thermodynamic stabilities are confirmed by the tolerance factor and negative formation energy. Moreover, by doping Ti ions into vacancy-ordered double perovskite A2SnY6, the effect of Ti doping on the electronic and optical properties was investigated in detail. Then, according to the requirement of practical applications in photovoltaics, the optimal concentration of Ti ions and the most suitable halide element are determined to screen the right compositions. In addition, the mechanical, electronic and optical properties of the selected compositions are discussed, exhibiting the maximum optical absorption both in the visible and ultraviolet energy ranges; thus, the selected compositions can be considered as promising materials for application in solar photovoltaics. The results suggest a great potential of A2Sn1-xTixY6 (A = K, Rb, Cs; Y = Cl, Br, I) for further theoretical research as well as experimental research on the photovoltaic performance of stable and toxic-free perovskite solar cells.
Project description:Recently, lead-free double perovskites have emerged as a promising environmentally friendly photovoltaic material for their intrinsic thermodynamic stability, appropriate bandgaps, small carrier effective masses, and low exciton binding energies. However, currently no solar cell based on these double perovskites has been reported, due to the challenge in film processing. Herein, a first lead-free double perovskite planar heterojunction solar cell with a high quality Cs2AgBiBr6 film, fabricated by low-pressure assisted solution processing under ambient conditions, is reported. The device presents a best power conversion efficiency of 1.44%. The preliminary efficiency and the high stability under ambient condition without encapsulation, together with the high film quality with simple processing, demonstrate promise for lead-free perovskite solar cells.
Project description:Lead-free organic-inorganic halide perovskites have gained much attention as nontoxic alternatives to CH3NH3PbI3 in next-generation solar cells. In this study, we have examined the geometric and electronic properties of methylammonium germanium iodide CH3NH3GeI3 using density functional theory. Identifying a suitable functional to accurately model the germanium halide perovskites is crucial to allow the theoretical investigation for tuning the optoelectronic properties. The performance of various functionals (PBE, PBE+D3, PBEsol, PBEsol+D3, HSE06, and HSE06+D3) has been evaluated for modelling the structure and properties. The calculation of electronic properties was further refined by using the quasiparticle GW method on the optimized geometries, and that has an excellent agreement with the experiment. We report from our GW calculations that the characteristic of the density of states for CH3NH3GeI3 resembles the density of states for CH3NH3PbI3 and the effective masses of the charge carriers of CH3NH3GeI3 are comparable to the effective masses of CH3NH3PbI3 as well as silicon used in commercially available solar cells.
Project description:Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2 AgBiBr6 , shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2 AgBiBr6 under ambient conditions. The band-gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag-Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band-gap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable band gaps for optoelectronic applications.
Project description:We report the synthesis and characterization of nanocrystals of a novel fully inorganic lead-free zero-dimensional perovskite, Cs4SnBr6. Samples are made of crystals with an average size of ∼20 nm with green emission centered around 530 nm. Interestingly, both colloidal suspensions and thin films show an enhanced air stability with respect to that of any other previous tin-based nanocrystalline system, with emission persisting for tens of hours under laboratory air.
Project description:Development of lead-free inorganic perovskite material, such as Cs2AgBiBr6, is of great importance to solve the toxicity and stability issues of traditional lead halide perovskite solar cells. However, due to a wide bandgap of Cs2AgBiBr6 film, its light absorption ability is largely limited and the photoelectronic conversion efficiency is normally lower than 4.23%. In this text, by using a hydrogenation method, the bandgap of Cs2AgBiBr6 films could be tunable from 2.18 eV to 1.64 eV. At the same time, the highest photoelectric conversion efficiency of hydrogenated Cs2AgBiBr6 perovskite solar cell has been improved up to 6.37% with good environmental stability. Further investigations confirmed that the interstitial doping of atomic hydrogen in Cs2AgBiBr6 lattice could not only adjust its valence and conduction band energy levels, but also optimize the carrier mobility and carrier lifetime. All these works provide an insightful strategy to fabricate high performance lead-free inorganic perovskite solar cells.
Project description:Lead-free double perovskites (DPs) will emerge as viable and environmentally safe substitutes for Pb-halide perovskites, demonstrating stability and nontoxicity if their optoelectronic property is greatly improved. Doping has been experimentally validated as a powerful tool for enhancing optoelectronic properties and concurrently reducing the defect state density in DP materials. Fundamental understanding of the optical properties of DPs, particularly the self-trapped exciton (STEs) dynamics, plays a critical role in a range of optoelectronic applications. Our study investigates how Fe doping influences the structural and optical properties of Cs2AgBiCl6 DPs by understanding their STEs dynamics, which is currently lacking in the literature. A combined experimental-computational approach is employed to investigate the optoelectronic properties of pure and doped Cs2AgBiCl6 (Fe-Cs2AgBiCl6) perovskites. Successful incorporation of Fe3+ ions is confirmed by X-ray diffraction and Raman spectroscopy. Moreover, the Fe-Cs2AgBiCl6 DPs exhibit strong absorption from below 400 nm up to 700 nm, indicating sub-band gap state transitions originating from surface defects. Photoluminescence (PL) analysis demonstrates a significant enhancement in the PL intensity, attributed to an increased radiative recombination rate and higher STE density. The radiative kinetics and average lifetime are investigated by the time-resolved PL (TRPL) method; in addition, temperature-dependent PL measurements provide valuable insights into activation energy and exciton-phonon coupling strength. Our findings will not only deepen our understanding of charge carrier dynamics associated with STEs but also pave the way for the design of some promising perovskite materials for use in optoelectronics and photocatalysis.
Project description:Lead halide perovskites are prospective candidates for CO2 photoconversion. Herein, we report copper-doped lead-free Cs2AgSbCl6 double perovskite microcrystals (MCs) for gas-solid phase photocatalytic CO2 reduction. The 0.2Cu@Cs2AgSbCl6 double perovskite MCs display unprecedented CO2 photoreduction capability with CO and CH4 yields of 412 and 128 μmol g-1, respectively. The ultrafast transient absorption spectroscopy reveals the enhanced separation of photoexcited carriers in copper-doped Cs2AgSbCl6 MCs. The active sites and reaction intermediates on the surface of the doped Cs2AgSbCl6 are dynamically monitored and precisely unraveled based on the in-situ Fourier transform infrared spectroscopy investigation. In combination with density functional theory calculations, it is revealed that the copper-doped Cs2AgSbCl6 MCs facilitate sturdy CO2 adsorption and activation and strikingly enhance the photocatalytic performance. This work offers an in-depth interpretation of the photocatalytic mechanism of Cs2AgSbCl6 doped with copper, which may provide guidance for future design of high-performance photocatalysts for solar fuel production.
Project description:In recent years, vacancy-ordered halide double perovskites have emerged as promising non-toxic and stable alternatives for their lead-based counterparts in optoelectronic applications. In particular, vacancy ordered Cs2PtI6 has emerged as a star material because of its high absorption coefficient, band gap of 1.37 eV, and long minority carrier lifetime. Despite substantial experimental research on this new class of material, theoretical simulations of their device properties remain scarce. In this work, a novel n-i-p device architecture (FTO/SnO2/Cs2PtI6/MoO3/C) is theoretically investigated using a solar cell capacitance simulator (SCAPS-1D). Theoretical investigations are carried out in order to optimize the device performance structure by varying the perovskite and selective charge transport layer thickness, absorber and interface defect density, operating temperature, back contact, series and shunt resistance, respectively. The optimized device showed an impressive power conversion efficiency (PCE) of 23.52% at 300 K, which is higher than the previously reported values. Subsequent analysis of the device's spectral response indicated that it possessed 98.9% quantum efficiency (QE) and was visibly active. These findings will provide theoretical guidelines for enhancing the performance of Cs2PtI6-based photovoltaic solar cells (PSCs) and pave the way for the widespread implementation of environmentally benign and stable perovskites.