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All-inorganic lead halide perovskite nanocrystals (NCs) have been widely investigated as highly promising optical gain materials due to their compelling electrical and optical properties. Although many efforts have been carried out, a deep understanding of perovskite NC vertical-cavity surface-emitting lasers (VCSELs) is elusive, which is very important in the development of photoelectronic integrated circuits. Along these lines, in this work, a low lasing threshold (22 μJ/cm2) single-mode VCSEL consisting of CsPbBr3 NCs film and two distributed Bragg reflectors was successfully constructed. The CsPbBr3 NCs were synthesized by using the supersaturated recrystallization method. Interestingly, benefiting from the strong coupling between the active layer and the optical field in the cavity, a single-mode lasing at 527 nm was demonstrated under femtosecond optical pumping. The carrier dynamics of the perovskite NC VCSEL was also thoroughly investigated by performing pump intensity-dependent time-resolved photoluminescence measurements. The typical gain-switching phenomenon was observed with an ultrafast decay of the laser pulse of ∼10 ps. Our work provides valuable insights for the implementation of the CsPbBr3 NC VCSEL for various optoelectronic applications.

Antimony sulfide (

The local breakdown behavior may be harmful to solar cells and could possibly permanently damage the cell. Therefore, understanding the breakdown mechanisms in commercially competitive photovoltaic devices such as monocrystalline silicon (Si) solar cells is of great importance. Here, by using the reverse-biased electroluminescence (ReBEL) imaging technique, we observed three types of breakdown phenomena in monocrystalline Si solar cells: defect-induced breakdown, avalanche breakdown, and early breakdown. We have applied a variety of methods to diagnose each breakdown mechanism. The positions of defect-induced breakdown were first determined by combining EL and ReBEL imaging. An innovation method, the distributed circuit modeling was further introduced to trace the formation of different defect-induced breakdown sites. It is firstly applied this approach in the analysis of the breakdown mechanism. Then, avalanche breakdown was demonstrated by the temperature coefficient. The origin of its emission spectra was analyzed by the Si energy band structure combined with Baraff theory. Moreover, the characteristic of early breakdown was found to be consistent with the Zener effect, which may be caused by the metal stains such as aluminum (Al) during the manufacturing process.

In this paper, Sb2S3 thin-film solar cells are fabricated by the vapor transport deposition (VTD) method. The effect of the source-substrate proximity on the performance of Sb2S3 thin-film solar cells has been investigated and comparative studies of different source-substrate proximity are carried out. The device efficiency is improved from 0.83 to 3.02% by optimizing the source-substrate proximity with the augment of open-circuit voltage, short-circuit current density and fill factor. X-ray diffraction and scanning electron microscopy studies indicate that the deposited Sb2S3 films can achieve optimal grain orientation, high crystallinity, and compact morphology. Moreover, the current transport mechanism is analyzed in detail from dark current density–voltage (J-V) measurements and shows the optimal sample to be least affected by Shockley-Read-Hall recombination and space-charge-limited current (SCLC). Meanwhile, temperature and light intensity-dependent open-circuit voltage measurements reveal the carrier recombination rates are lowest for the optimal cell in all regions, including the CdS/Sb2S3 interface, the space-charge region (SCR), and the quasi-neutral region (QNR). These can account for the efficiency enhancement of the optimal cell and can be used to facilitate the further development of Sb2S3 thin-film solar cells.

Despite many successful realizations of laser operations in various micro/nanostructured lead halide perovskites (LHPs), the electron–hole plasma (EHP) lasing dynamics has only rarely been reported...

In this paper, we demonstrate numerical evidence that interfacial passivation in the Sb2Se3 solar cell forming the configuration of indium tin oxide (ITO)/SnO2/CdS/Sb2Se3/Au is beneficial for suppr...

Superstrate ITO/CdS/Sb2Se3/Au thin-film solar cells were fabricated with a CdS film produced by a radio-frequency (RF) magnetron-sputtering method as the buffer layer. The effect of the CdS layer thickness (70–120 nm) on the properties of Sb2Se3 thin films and the performance of the solar cells was investigated. The optimal CdS thickness was 90 nm, which led to the best power conversion efficiency of 5.91%; to the best of our knowledge, this is the highest efficiency for Sb2Se3 solar cells with a sputtered CdS buffer layer to date. X-ray diffraction and scanning electron microscope results indicated that the Sb2Se3 films grown on 90-nm-thick CdS layers had the optimal grain orientation and the best morphology. The current–voltage (J–V) and admittance results indicated that the Sb2Se3 cell with a 90-nm-thick CdS layer had the lowest saturation current and the smallest defect densities. Moreover, temperature- and light intensity-dependent open-circuit (Voc) measurements revealed that the carrier recombination rates at the CdS/Sb2Se3 interface, space-charge region (SCR), and quasi-neutral region (QNR) all achieved the smallest value for the Sb2Se3 cells with a 90-nm CdS buffer layer. These data account for the optimal cell performance and offer new research directions for solving challenges of chemical bath deposition of CdS in Sb2Se3 solar cells.

Electronic transport mechanisms in Sb2Se3 thin-film solar cells were investigated using temperature-dependent current-voltage (J-V) measurements. Sb2Se3 thin films were deposited via the vapor transporting deposition method using a double-temperature-zone tubular furnace system, and comparative studies were performed for Sb2Se3 films formed on substrates located at three different positions away from the furnace center. The device efficiency varied from 3.83 to 6.24%. First, structural properties obtained by X-ray diffraction, Raman and scanning electron microscopy measurements verified the optimal Sb2Se3 film quality for the cell with the highest efficiency. Then, temperature-dependent saturation current and open-circuit voltage (Voc) measurements revealed that the dominant carrier recombination occurred in the CdS/Sb2Se3 interface region, which possibly influenced the Voc for all cells: the highest Voc for the optimal Sb2Se3 cell was at least partly due to it having the lowest CdS/Sb2Se3 interface recombination rate. Finally, the reverse bias current relationship revealed that non-ohmic shunt current (space-charge-limited current, SCLC) plays an important role in affecting the performance of solar cells, as lower-efficiency cells had higher non-ohmic shunt current.

A two-dimensional distributed resistance model has been used to simulate the measured dark current-voltage (J-V) curve and the absolute electroluminescence (EL) images of a GaAs solar cell, with the deviation between the simulated and experimental results smaller than 5%. The effects of different kind of defects on the EL distributions with various current densities were also analyzed, and it has been demonstrated that it was possible to identify the defects by analyzing the current-density dependent EL distributions and also by analyzing the current-density dependent voltage difference (ΔV) between the defects and normal points.

This study reports ultraviolet picosecond random lasing (RL) based on multiphoton absorption in zinc oxide (ZnO) nanopowders with a mean size of ∼100 nm under femtosecond optical excitation. Upconversion random lasing is achieved with an excitation wavelength increasing from 600 to 1800 nm, corresponding to a five-photon excitation. The RL threshold has a slight positive relationship with excitation wavelength, except for a significant increase with four-photon excitation at 1200–1300 nm, demonstrating promising upconversion lasing properties of ZnO nanopowders. A remarkably lower RL threshold is observed at long excitation wavelengths ranging from 1500 to 1800 nm than that for four-photon pumping (1200–1300 nm) processes. Defect states in ZnO are suggested to be the reason that results in the excitation wavelength dependence of random lasing. Transient RL characteristics are investigated using time-resolved photoluminescence measurements, with the RL pulse delay time and pulse width observed to decrease ...

Aluminum doped ZnO thin films (AZO), which simultaneously transmit light and conduct electrical current, are widely applied in photovoltaic devices. To achieve high performance AZO thin films, the effects of RF magnetron sputtering conditions on the optical and electrical properties of the films has been explored. The optimized AZO thin films exhibit strong (002) orientated growth with hexagonal wurtzite structure. The minimum resistivity of 0.9Í10-3 Ω·cm, the highest carrier concentration of 2.8Í1020 cm-3, the best Hall mobility of 22.8 cm2·(V·s)-1 and average transmittance above 85% can be achieved at the optimum deposition condition of 0.2 Pa, 120 W and 200 °C. Considering the single parabolic band model, the bandgap shift by carrier concentration of the films can be attributed to the Burstein-Moss effect. The results indicate that RF magnetron sputtered AZO thin films are promising for solar cell applications relying on front contact layers.

Electron tunneling dynamics in asymmetric coupled triple InGaN/GaN quantum wells (ACQWs) with different well thicknesses of 3.0 nm (QW1), 2.5 nm (QW2), and 2.0 nm (QW3) were quantitatively investigated based on the time- and spectrally-resolved photoluminescence (PL) measurements and the rate-equation theory. Under weak excitation, only the emission peak of the widest well was observed at room temperature due to the effective electron tunneling from a wide to a narrow well, while all three emission peaks of the distinct wells were obtained at a high excitation level. The PL-intensity ratios of the wells in the initial transient spectra differed from those in the time-integrated spectra. With a set of rate equations and the experimental results of PL ratios and decay times, a 2 ns tunneling time from QW2 to QW1 was extracted and was decreased to 0.5 ns with increasing excitation, while the one from QW3 to QW2 was extracted to be ∼ 170 p s . The extracted tunneling times are in good qualitative agreement with the data from the exponential fitting of the PL decay traces, which can be interpreted by the energy mismatches between relevant energy levels in the ACQWs. These results provide not only a better understanding of the carrier recombination and tunneling processes in the ACQW systems but also a useful guidance for high-performance ACQW-based optoelectronic and functional devices.

The photoluminescence spectra of the InP/ZnS quantum dots (QDs) and the composite structure of the InP/ZnS QDs coupled with Au nanorods are investigated in this paper. In the luminescence spectra of the two samples, the recombination of the bright–dark doublet exciton states and an upper bright exciton state are observed at the temperature 11–130 K. The temperature dependence of the main emission peaks of the InP/ZnS QDs and the composite structure can be expressed by the Varshni expression in the temperature range of 11–300 K. The coupling between the QDs and the surface plasmon resonance (SPR) states has a great effect on the exciton recombination and the defect recombination. Because of the coupling, the variation range of the main emission peak of the composite structure is about 28 meV more than the pure QDs with the temperature from 11 K to 300 K. The red shift of the defect emission with increasing temperature is coincident with the red shift of the SPR energy with increasing temperature. The experimental results confirm that the energy transfer from the SPR states is the main source of the defect emission.

Hybrid organic–inorganic metal halide perovskites are currently arousing enthusiasm and stimulating huge activity across several fields of optoelectronics due to their outstanding properties. In this study, we present the incoherent random lasing (RL) emissions from CH3NH3PbBr3 perovskite thin films on both planar fluorine-doped tin oxide (FTO) substrates and patterned sapphire substrates (PSSs). A detailed examination of the spectral evolution indicates that inelastic exciton–exciton scattering called P-emission is the most plausible mechanism accounting for the lasing emissions. The RL threshold of the perovskite films on PSSs is found to be effectively reduced by more than one order of magnitude from 2.55 to 0.15 μJ per pulse compared to that on FTO substrates. The giant threshold reduction is ascribed to the enhanced random scattering of light and the photon recycling induced by the multireflection processes at the perovskite/PSS interface, which increases the likelihood that the inoperative random rays will re-enter the possible optical loops formed among the perovskite particles, resulting in considerable optical resonance enhancement. The simulation results reveal that the light extraction efficiency on the top facet of the perovskites is significantly increased by approximately 155% by utilizing the PSS instead of the FTO substrate. Moreover, the first direct experimental observation of the multireflection phenomenon of light, as well as the dynamic processes of photon propagation in the composite PSS structure, is presented by Kerr-gate-based time-resolved photoluminescence. Our results provide an effective strategy to achieve high-performance perovskite random lasers and novel light-emitting devices for speckle-free full-field imaging and solid-state lighting applications, by introducing ingeniously designed periodic nano-/microscale optical structures.

Antimony selenide (${\text{Sb}_2}{\text{Se}_3}$Sb

The defect properties of

Sb2Se3 thin films prepared by vapor transport deposition (VTD) method have been treated by post annealing process at 200 °C in vacuum condition for 1 h, and the comparative studies between the post annealing treatment (PAT) and without the treatment were carried out. The device efficiency was improved from 4.89% to 5.72% by PAT via the augment of open-circuit voltage and fill factor. Electrical properties from dark J-V and C-V measurements, structural properties from X-ray diffraction, Raman and scanning electron microscope measurements, defect properties from admittance measurements have been compared for the two cell samples. The Sb2Se3 cell sample with PAT was found to own less parallel current pathways, larger built-in voltage, better crystalline and lower defects densities, which may account for the efficiency enhancement.

Admittance measurements were performed on Sb2Se3-based thin-film solar cells with energy conversion efficiencies from 3.85% to 5.91%. Three defects located at different energy levels above the valence band maximum (VBM) in the ranges of 0.3–0.4, 0.2–0.6 and 0.5–0.6 eV were identified for all cells and denoted D1, D2 and D3, respectively; the exact energy level of each defect within these ranges varied between cells. Correlations between the defect properties and the cell efficiencies were investigated and it was found that the activation energies of both D1 and D2 increased with decreasing efficiencies, the capture lifetime of holes increased with increasing efficiencies for both D1 and D2, and no obvious relationship with efficiency was found for D3. This indicated that D1 and D2 may play more important roles that affect the efficiencies in the measured samples. DC reverse bias-dependent admittance measurements enabled identification of D1 and D2 as bulk-type defects while D3 was identified as an interface or near-interface type defect. Finally, large parasitic series resistance and inductance effect, instead of defects, were considered to dominate the admittance spectra in the high frequency range (> 105 Hz).

Externally induced strain effect was investigated in GaAs thin-film solar cells by electroluminescence (EL) imaging method. The strained regions demonstrated not only enhancement of local EL intensity but also redshift of the EL emission peaks. The observations were explained well by a gradient quantum-well (GQW) model correlated with tensile strain in the GaAs thin films. External biaxial strain was considered in this model which was accordingly obtained from the energy shift of the EL spectra. Finally, the spatially resolved strain in GaAs thin-film solar cells was obtained from the EL images by relating the EL emission intensity to the shift of the EL spectra. This work provides a potential standard method for diagnosis of externally induced strain in thin-film solar cells by EL measurements.

Organometallic halide perovskites have been demonstrated to be very promising for nonlinear optics and practical frequency upconversion devices in integrated photonics. In this work, high quality o...

High power pulsed lasers with tunable pulse widths are highly favored in many applications. When combined with power amplification, gain-switched semiconductor lasers driven by broadband tunable electric pulsers can meet such requirements. For this reason, we designed and produced a low-cost integrated CMOS pulse generator with a minimum pulse width of 80 ps and a wide tuning range of up to 270 ns using a 40-nm microelectronic process technique. We used this pulser to drive a 1.3-µm semiconductor laser diode directly, and thereafter investigated the gain-switching properties of the laser system. The optical pulses consist of a spike followed by a steady state region. Tuning the width of the electrical pulse down to approximately 1.5 ns produces optical pulses consisting only of the spike, which has a minimum pulse-width of 100 ps. Moreover, the duration of the steady state can be tuned continuously by tuning the electrical pulse width, with a peak power of approximately 5 mW. The output voltage of the electric pulser has a tuning range of 0.8–1.5 V that can be used to directly drive semiconductor laser diodes with wavelengths in the near-infrared spectrum, which are suitable for power amplification with rare-earth doped fiber amplifiers.

Slightly Mn and Mg co-doped BiFeO 3 films (BiFeO 3 , BiFe 0.95 Mg 0.01 Mn 0.04 O 3 , BiFe 0.94 Mg 0.02 Mn 0.04 O 3 and BiFe 0.93 Mg 0.03 Mn 0.04 O 3 , xBFMMO, x = 0, 0.01, 0.02 and 0.03) have been grown on Si (1 0 0) substrates by sol-gel technique. Rhombohedral lattice structure and phase transition is confirmed by X-ray diffraction and Raman spectroscopy. The improved surface morphology and decreased grain size of films can be observed in SEM micrographs due to the influence of Mn and Mg co-doping. Blue emissions of xBFMMO films can be found in Photoluminescence spectra, meanwhile the nonlinear shift of emission peaks imply the variation of bandgap. Room-temperature magnetization versus magnetic field ( M - H ) curves exhibit enhanced saturation magnetization compared with parental BiFeO 3 , which can attribute to destroyed spin cycloid and released locked magnetization. These properties offer a great potential on the multiferroic information storage application.

We studied the material and photovoltaic properties of Sb

Perovskite nanocrystals (PNCs) have emerged as highly promising optical gain materials for laser applications. Despite the recent surge of reports on their lasing performance, it remains a challenge to achieve PNCs-based single-mode vertical cavity surface emitting lasers (VCSELs) because of their inhomogeneous gain saturation. Here, we successfully demonstrate high performance single-mode VCSELs using CsPbBr3 PNCs that were synthesized via a facile ligand-assisted reprecipitation strategy. The optical gain medium with wide crystal size range was fabricated, and the dense assembly of each individual PNCs was expected to offer a homogeneous optical continuum to reduce gain saturation inhomogeneity. The fabricated VCSELs exhibit excellent single-mode lasing at ~541 nm without mode hopping and high spontaneous emission coupling factor of ~0.24, which is one order of magnitude higher than those of nitride-based VCSELs. Through streak camera direct observations, the stimulated emission of the laser device exhibits an ultrafast decay of ~10 ps, and the electron hole plasma (EHP) mechanism is considered responsible for stimulated emission in the VCSELs. This work paves the way toward next-generation high performance PNC-based single-mode laser devices with reduced fabrication cost for practical application.

The combination of lasers and solar cells has potential applications in many areas. Therefore, investigating the laser induced damage and defect formation in such cells is crucial. In this study, a Cu(In, Ga)Se2 solar cell was irradiated with a 532 nm continuous wave laser beam. The damage threshold power density with irradiation for 10 s was found to be approximately 5000 W/cm2 by analyzing the light current density–voltage curves and the variation of the solar cell efficiency after laser exposure. Further, absolute electroluminescence (EL) imaging with distributed circuit modeling was used to determine the laser induced defects. By simulating the measured injection current dependent EL intensities of the defect spots, the defects created by exposure to laser power densities less than 5000 W/cm2 could be mainly attributed to increased series resistance or increased transparent conductive oxide layer resistance, whereas those created by exposure to laser power densities greater than 5000 W/cm2 could be mainly attributed to decreased shunt resistance.

Current defect inspection methods for photovoltaic (PV) devices based on electroluminescence (EL) imaging technology lack juggling both labor-saving and in-depth understanding of defects, restricting the progress towards yield improvement and higher efficiency. Herein, we propose an adaptive approach for automatic solar cell defect detection and classification based on absolute EL imaging. Specifically, we first develop an unsupervised algorithm to automatically detect defects referring to the defect features in EL images. Then a diagnosis approach is proposed, which statistically classifies the detected defects based on the electrical origin. To the best of our knowledge, the proposed method is the first effort to integrate automatic defect detection with fine-grained classification. Experimental results on multiple types of solar cells show that the proposed method can achieve the average uncertainty of 5.15% at the minimum, with by up to 98.90% optimization ratio compared with two conventional methods. The proposed method is expected to provide more guiding feedback in both practical design and reliability diagnosis of the PV industry.

In this study, Sb2(S,Se)3 thin films are fabricated using the vapor transport deposition (VTD) method, with Sb2Se3 and Sb2S3 mixed powders as the evaporation source. The performance of the corresponding glass/ITO/CdS/Sb2(S,Se)3/Au solar cells are found to be correlated to the mass ratio between Sb2S3 and the overall powder mixture. The properties of the Sb2(S,Se)3 thin films and cell devices adopting four different Sb2S3 mass ratios (x = 0.1, 0.25, 0.5 and 0.75) are compared. Further, the electrical properties – from dark and light J-V measurements; structural properties – from X-ray diffraction and scanning electron microscope measurements; and carrier-recombination rates at the buffer/absorber interface in the space-charge region (SCR) and in the quasi-neutral region – from temperature-illumination-dependent open-circuit voltage (VOC) measurements – are compared. It is found that a Sb2(S,Se)3 solar cell with a Sb2S3 mass ratio of 0.25 had optimal crystallinity, the lowest density of deep traps and the smallest carrier-recombination rates at the interface, leading to a high efficiency of 7.31%.

BiFe1−xCrxO3 (xBFCO, x=0, 0.03, 0.06 and 0.09) polycrystalline films have been prepared on quartz substrates by a sol–gel technique. X-ray diffraction clearly reveals the crystal structure of xBFCO thin films transforms from rhombohedral to orthorhombic, moreover, inter planar spacing and grain size of xBFCO are reduced slightly. Scanning electron microscopy shows that Cr doping can improve surface morphology and reduces the average grain size of the films. The photoluminescence (PL) spectra of xBFCO thin films at room temperature show a strong emission in the blue region. With increasing x from 0.00 to 0.09, the band gap (Eg) of xBFCO films decreases and can be expressed by Eg=(2.58−0.67x) eV. Compared with BiFeO3 film, the saturation magnetization of xBFCO (x=0.03, 0.06 and 0.09) films is significantly enhanced, which provides potential applications in information storage.

All-inorganic perovskite micro/nanolasers are emerging as a class of miniaturized coherent photonic sources for many potential applications, such as optical communication, computing, and imaging, owing to their ultracompact sizes, highly localized coherent output, and broadband wavelength tunability. However, to achieve single-mode laser emission in the microscale perovskite cavity is still challenging. Herein, we report unprecedented single-mode laser operations at room temperature in self-assembly CsPbX 3 microcavities over an ultrawide pumping wavelength range of 400–2300 nm, covering one- to five-photon absorption processes. The superior frequency down- and upconversion single-mode lasing manifests high multiphoton absorption efficiency and excellent optical gain from the electron–hole plasma state in the perovskite microcavities. Through direct compositional modulation, the wavelength of a single-mode CsPbX 3 microlaser can be continuously tuned from blue-violet to green (427–543 nm). The laser emission remains stable and robust after long-term high-intensity excitation for over 12 h (up to 4.3 × 10 7 excitation cycles) in the ambient atmosphere. Moreover, the pump-wavelength dependence of the threshold, as well as the detailed lasing dynamics such as the gain-switching and electron–hole plasma mechanisms, are systematically investigated to shed insight into the more fundamental issues of the lasing processes in CsPbX 3 perovskite microcavities.

Obtaining whispering gallery mode (WGM) lasing with prominent stability and high quality optical cavities is extremely desirable but still a great challenge. Despite the recent surge of reports on microspheres, nanowires and nanoplatelets metal halide crystals, there has few reports on the morphology of Hemispheres (HSs) in the form of uniform, component-tunable microcrystals. Here, CsPbX3 (X = Cl/Br) HSs with smooth surface and regular geometry structure were synthesized on silicon substrates by chemical vapor deposition (CVD) method, and the wavelength of laser can be continuously tuned from blue to green (450–540 nm) at room temperature by varying the halide composition. WGM laser with polarization ratio of 0.70 and cavity quality factor Q of 2485 were realized in the CsPbBr3 HS cavity. Besides, the crystal cavity suggested a high photonic and thermal stability for the superb capability of continuous stable lasing output under ambient conditions. All these results illustrate that the synthesis of cesium lead halide perovskite HSs may provide an alternative solution for fundamental researches and applications in optical devices.

The effect of the Cu/Ga ratio on properties of deep-level defects in CuGaSe