Figure - available from: Journal of Materials Science: Materials in Electronics
This content is subject to copyright. Terms and conditions apply.
a Actual thin film samples; b the schematic photoresponse measurement system, where conductive channel is length (L) = 1 mm and width (W) = 100 μm, and the arbitrary waveform generator produces pulse control signal to control the 405 nm laser on and off
Source publication
We proposed the preparation of the compound thin film of CsPb2Br5 and CsPbBr3 perovskites via thermal evaporation method with post-annealing. The optical absorption, energy gap, and photoresponse properties of the compound thin films were investigated. Over 90% transmittance in visible region of 550–700 nm was obtained, and the energy gap of thin f...
Citations
... The absorption coefficient (α), photon energy (hν) and the optical energy gap are related through the known Tauc relation [30,31]: ...
Thin films of Bi2Te3 alloy were grown by vacuum thermal evaporation (VTE) and pulsed laser deposition (PLD) techniques. The growth was conducted on clean substrates of non-conductive glass. X-ray diffraction (XRD) analysis was used to study the materials crystal structure. The XRD patterns revealed the crystalline nature of the prepared films. Surface morphology was investigated by the atomic force microscopy (AFM) showing that the films are formed of crystallites bounded by twin boundaries oriented in the c-axis in a way that perpendicular to the substrate plane. The samples shown to be stoichiometric and of good morphology. Transmission and reflection spectral have been obtained at room temperature using a double beam Jasco spectrophotometer. Absorption coefficient, extinction coefficient and refractive index were determined. The optical band gap was evaluated by measuring the fundamental absorption and extrapolation of the linear portion of (αhν)² versus hν plots. The plots indicated direct allowed transition. Comparison between all optical parameters of the films prepared by the two different methods has been performed.
The CsPbX3 perovskites have demonstrated promising applications in the field of X-ray detection. Appropriate element doping to substitute Pb in CsPbX3 not only improves the photoresponse performance of the resulting material but also reduces the Pb content for achieving environmental protection. Herein, X-ray detectors based on Sr-doped CsPb1-x Sr xBr3 thick films were developed. The effects of Sr doping concentration were investigated. The incorporation of Sr increased the density of the CsPbBr3 thick film and modulated the bandgap of the materials. CsPb1-x Sr xBr3 exhibited good optical responses at different bias voltages and X-ray doses. The X-ray response improved as the Sr-doping concentration increased. Therefore, the partial substitution of Sr into CsPbBr3 is suitable for reducing the Pb content in X-ray detectors. Furthermore, the development of CsPb1-x Sr xBr3 thick films provides a new strategy for the detection of X-rays.
Aims
This work reported a 405 nm photodetector based on the thermal evaporated CsPbBr3-CsPb2Br5 compound thin film.
Background
The post-annealing process of the CsPbBr3-CsPb2Br5 compound thin film prepared by thermal evaporation method has been improved in this work. To enhance the crystallization and photoresponse properties of the thin films, dimethyl sulfoxide (DMSO) steam was used in post-annealing process, instead of using the previous way that increased the annealing temperature.
Methods
The CsPbBr3-CsPb2Br5 compound powder was deposited directly on surface glass substrate by thermal evaporation to form CsPbBr3-CsPb2Br5 compound thin film. The thin films were post-annealed at 150 oC for 15 min to crystallize. The DMSO liquid was dropped on the substrate, and then the liquid would be evaporated completely to become DMSO steam during 150 oC post-annealing. The DMSO steam would cover the thin film completely to help the crystallization. Finally, the gold electrodes were deposited on surface of thin films with a conductive channel of 1 mm * 100 µm.
Result
Results showed that the crystalline quality of the thin film after DMSO steam annealing was greatly improved compared with that of thin film without DMSO steam annealing. The energy gap was between 2.355 eV and 2.293 eV, which was similar to the previous report. In addition, under 405 nm excitation, the photocurrent of the thin film annealed in DMSO steam showed the rapid response (35 ms), good light radiation power dependence of the photocurrent and the improved responsivity. Especially, the responsivity at 3 V bias of the thin film annealed in DMSO steam increased to 1.5 times that of the thin film without DMSO steam annealing and even 4.5 times that of as-deposited film.
Conclusion
A 405 nm photodetector based on the thermal evaporated CsPbBr3-CsPb2Br5 compound thin film was prepared successfully. The newest report has improved the preparation process of CsPbBr3-CsPb2Br5 compound thin films, where low annealing temperature with the DMSO steam assisted post-annealing process was used. The thin film annealed in DMSO steam possesses high crystalline quality and enhanced photoresponse performances, compared with thin film without DMSO steam annealing.
Thin layers of Bi2-chalcogenides, in the form of Bi2(Se1-xTex)3 films, were evaporated on glass substrates by means of the vacuum thermal evaporation. Microstructure of the as prepared layers was investigated by x-ray diffraction (XRD) analysis. Identifications of the surface morphology and roughness were determined via scanning electron microscope (SEM). Optical transmissivity spectra proved that the as prepared films have low transparency with growing trend upon increasing the wavelength beyond the infra-red region. Low transmittance was observed for the as prepared films. Heat treatment, in the form of temperature annealing, was carried out aiming at boosting the structural features and the materials transmissivity. Structural properties and surface features of the annealed films were probed also via XRD and SEM analyses. It was found that the crystal size increases while the micro-strain and the dislocation density decrease obviously due to annealing. It was also observed that the annealing process significantly enhances the materials transmission especially in the range of higher wavelengths. Optical band gap was studied after annealing at various temperatures. Notable change in the band gap value was observed as a result of annealing. The band gap of the undoped (Bi2Se3) materials showed significant rise from 0.14 to 1.79 eV due to annealing. Similarly, the Te-doped samples exhibited notable increase in their band gap values after annealing. For example, the optical band gap of the sample doped at x = 0.20 increased from 0.03 to 0.41 eV by annealing. On the other hand, transmittance was also enhanced by annealing. For samples treated at 250 °C for 3 h, their optical transmissivity is enhanced to over 99% at the visible near-IR range. Such significant enhancement can be ascribed to structural enhancements. With such enhancement in the optical transmissivity, optoelectronic applications including transparent electrode can be met.
In this chapter, we review the breakthrough of photodetectors based on perovskite quantum dots (QDs). We first give the unique features of perovskite QDs for application in photodetectors. Then, we elaborate some important photodetector performance metrics, underlying physical mechanism, and device structure for photodetectors based on perovskite QDs. Moreover, we present the recent development of photodetectors based on pure perovskite QDs sorted by response wavelength. Meanwhile, we demonstrate the photodetectors based on hybrid perovskite QDs by introducing the functional materials. The future of photodetectors based on perovskite QDs is highlighted in the last section.
In the present study, the successful fabrication, through a surfactant-free one-pot synthesis in ethanol solution, of the all-inorganic halide perovskite CsPbBr3 has been achieved. The phase formation has been obtained for the first time, using the β-diketonate complexes [Pb(hfa)2diglyme]2 and Cs(hfa) (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2-methoxyethyl ether) and Br2 as the precipitating agent. The growth of CsPb2Br5 microcrystals has been obtained and stabilized under specific synthetic conditions, by controlling the phase transition from CsPbBr3 to CsPb2Br5 as well. The entire process was operated under acid-catalyzed conditions without any need of humidity control and hazardous organic solvents. The control of the aging time and the phase stability during the heat treatment represent the key points in order to selectively and reproducibly obtain the CsPbBr3 or CsPb2Br5 phases. Structural, morphological, and compositional characterizations of the final product show the formation of square microcrystals, with a grain size of up to 3 μm, of the pure and stable perovskite CsPbBr3 phase. Finally, promising results in photocatalytic degradation tests using rhodamine B solution have been obtained under UV light (λ = 360 nm) and visible light, showing high degradation yields of up to 81.9% and 58.4% for CsPbBr3 and CsPb2Br5, respectively.
A simple solvent-free, versatile, and flexible route for material properties modulation in halide perovskite thin films has been developed using CsPbBr3 thin films. The method further enables composition and morphology control using a solid-state ion-exchange reaction in the presence of PbX2 (X= Cl, Br, I) vapor in a close-spaced sublimation deposition system. The morphology, structure, and optoelectronic properties of the resulting CsPb(Br1–xXx)3 (X = Cl, Br, I) films, as well as the performance of PN junction diodes are systematically investigated and discussed. The CsPb(Br1–xXx)3 films maintained an orthorhombic structure with increased mobility and remarkable grain growth with grains as large as 25 μm in films as thick as 8 μm. The CsPb(Br1–xXx)3 films enabled diodes with a very low leakage current (1 × 10–8 A/mm2), likely due to the large crystalline grains. The diodes were used as radiation detectors, with superior alpha particle sensing from a 210Po source. This simple, scalable, solution-free, and cost-effective perovskite annealing process can be applied in other perovskite systems to also tune their band gap in the range of 1.7–2.9 eV and tailor their transport electronic properties to further expand the application of these exceptional materials.
Herein propose a high performance dye sensitized solar cell based terbium (Tb) doped barium titanate (BaTiO3) thin films prepared by three different techniques such as chemical bath deposition method (CBD), screen printing (SP) and spray pyrolysis coating (SPC) techniques respectively. XRD, SEM and HRTEM results suggest that tetragonal phase of BaTiO3 with three different morphologies like spherical, nanosheets and nanofibers for CBD, SP and SPC assisted Tb:BTO thin films, respectively. Enhancing the visible light absorption, narrowing the band gap energy and prevent the recombination process of electron-hole pair of SPC assisted Tb:BTO thin films were also examined by UV and PL spectra analysis. Moreover, the SPC assisted Tb:BTO thin films show high surface area (102.5 m²/g) and specific porous nature (14.7 nm), studied by N2 adsorption-desorption analysis. Sandwich type DSSC was fabricated and studied the current-voltage characteristic of all the Tb:BTO thin film photoanode samples. The device utilizing in the SPC assisted Tb:BTO thin film photoanode produced the highest photo-conversion efficiency (η) of 15.15% than compared with CBD assisted Tb:BTO (6.57%) and SP assisted Tb:BTO (8.67%). This is due to highest porosity, surface area, lowest leak current and charge transfer resistance Rct of Tb:BTO photoanode. The improved mechanism of the proposed work is also discussed in detail.
