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Geometry Distortion and Small Polaron Binding Energy Changes with Ionic Substitution in Halide Perovskites
摘要： Halide perovskites have demonstrated remarkable performance in optoelectronic applications. Despite extraordinary progress, questions remain about device stability. We report an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies of several experimentally relevant halide perovskites using isolated clusters. Local lattice symmetry, electronic structure, and electron-phonon coupling are interrelated in polaron formation in these materials. To illustrate this, first principles calculations are performed on (MA/Cs/FA)Pb(I/Br)3 and MASnI3. Across the materials studied, electron small polaron formation is manifested by Jahn-Teller like distortions in the central octahedron, with apical PbI bonds expanding significantly more than the equatorial bonds. In contrast, hole polarons cause the central octahedron to uniformly contract. This difference in manifestation of electron and hole polaron formation can be a tool to determine what is taking place in individual systems to systematically control performance. Other trends as the anion and cations are changed, are established for optimization in specific optoelectronic applications.
关键词： optoelectronic applications,reorganization energies,Jahn-Teller distortions,charge density,Halide perovskites,small polaron formation,electronic structure
更新于2025-09-09 09:28:46
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Crystal facet engineering induced anisotropic transport of charge carriers in a perovskite
摘要： Precise control of crystal orientations and macroscopic morphology of a perovskite crystal is crucial for various optoelectronic applications relying on charge carrier transport tuning along exposed crystal facets. Here, taking methylammonium lead bromide (CH3NH3PbBr3) as an example, and employing a novel crystal facet engineering method, we successfully construct two kinds of perovskite crystals with exposed {001} and {110} facets. We find that the free carriers’ photoluminescence lifetime on the {001} facets can be 3 times longer than that on {110} facets. The related mechanisms are investigated via fluorescence lifetime imaging microscopy and in situ transmission electron microscopy. These indicate that the different trap state density of exposed facets and crystal structure changing of CH3NH3PbBr3 under light and electron beam irradiation lead to the differences in carrier transport along different facets. By distinguishing the charge carrier transport on different CH3NH3PbBr3 exposed facets, micro-photodetectors have been constructed. A device fabricated with the {001} exposed facets exhibited two orders of magnitude higher photocurrent and half as much dark current as a {110} facet-based device. Thus, the crystal facet engineering of perovskites can be widely adopted for understanding physical/chemical properties of perovskite crystals and provides great potential for novel perovskite optoelectronic device applications.
关键词： crystal facet engineering,charge carrier transport,optoelectronic applications,photodetectors,perovskite
更新于2025-09-09 09:28:46
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Charge Mobility and Recombination Mechanisms in Tellurium van der Waals Solid
摘要： Trigonal tellurium is a small band gap elemental semiconductor consisting of van der Waals bound one-dimensional helical chains of tellurium atoms. We study the temperature dependence of the charge carrier mobility and recombination pathways in bulk tellurium. Electrons and holes are generated by irradiation of the sample with 3 MeV electrons and detected by time-resolved microwave conductivity measurements. A theoretical model is used to explain the experimental observations for different charge densities and temperatures. Our analysis reveals a high room temperature mobility of cm2V-1s-1. The mobility is thermally deactivated suggesting a band-like transport mechanism. According to our analysis charges predominantly recombine via radiative recombination with a radiative yield close to 98%, even at room temperature. The remaining charges recombine by either trap-assisted (Shockley-Read-Hall) recombination or undergo trapping to deep traps. The high mobility, near unity radiative yield and the possibility of large-scale production of atomic wires by liquid exfoliation make Te of high potential for next-generation nanoelectronic and optoelectronic applications, including far-infrared detectors and lasers.
关键词： recombination mechanisms,charge mobility,optoelectronic applications,Tellurium,van der Waals solid
更新于2025-09-04 15:30:14
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Tellurium-based Double Perovskites A2TeX6 with Tunable Bandgap and Long Carrier Diffusion Length for Optoelectronic Applications
摘要： Lead-free hybrid perovskites have attracted immense interest as environmentally friendly light absorbers. Here, we report on tellurium (Te)-based double perovskites A2TeX6 (A= MA, FA or BA, X = Br- or I-, MA= CH3NH3, FA= CH(NH2)2, BA= benzylamine) as potentially active materials for optoelectronic devices. This perovskites exhibit a tunable bandgap (1.42 eV-2.02 eV), a low trap density (～1010 cm-3), and a high mobility (～ 65 cm2 V-1 s-1). Encouragingly, the MA2TeBr6 single crystal with a bandgap of 2.00 eV possesses a long carrier lifetime of ~6 μs and corresponding carrier diffusion lengths of ~38 μm, which are ideal characteristics for a material for photodetectors and tandem solar cells. Moreover, A2TeX6 perovskites are relatively robust in ambient conditions, being stable for at least two months without showing any signs of phase change. Our findings bring to the forefront a family of lead-free Te-based perovskites for non-toxic perovskite optoelectronics.
关键词： Optoelectronic applications,Long carrier diffusion length,Tunable bandgap,Tellurium-based double perovskites
更新于2025-09-04 15:30:14