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Electrically Tunable Liquid-Crystala??Polymer Composite Laser with Symmetric Sandwich Structure
摘要： This study investigates and develops for the first time an electrically tunable liquid-crystal?polymer composite laser with a symmetric sandwich structure. This structure includes two identical polymer-stablized cholesteric liquid-crystal (PSCLC) layers, and a dye-doped nematic LC (DDNLC) layer is sandwiched between them. The PSCLC and DDNLC layers act as distributed Bragg reflectors and half-wave plate with a gain medium, respectively. The entire cell behaves as an optical cavity, where the resonant modes occur at the maxima of the cell’s transmission spectrum. Through the competition among the resonant modes by considering the gain and loss, the resonant mode with the lowest lasing threshold can be sieved out for lasing occurrence. When the same voltage is applied to the two PSCLC layers, the pitch gradients are simultaneously formed through the two layers because of the electrically induced ion-concentration gradients. When the voltage increases, the pitch gradients increase, thereby leading to the expansion of the cell photonic band gap (PBG) and blue shift of the lasing wavelength. The sandwich cell PBG can expand from 55 nm to over 170 nm, and the tuning range of the lasing wavelength is as high as 70 nm, which is the widest ever achieved in LC-related sandwich systems. The proposed configuration of the sandwich sample presents new insights into tunable LC PBG and laser devices, thereby providing potential applications in the form of sensors, medical imaging, displays and lighting, among others.
关键词： distributed Bragg reflectors,electrically tunable,dye-doped nematic LC,photonic band gap,liquid-crystal?polymer composite laser,optical cavity,symmetric sandwich structure,half-wave plate,lasing wavelength,polymer-stablized cholesteric liquid-crystal
更新于2025-09-19 17:13:59
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Tunnel oxide passivating electron contacts for high‐efficiency n‐type silicon solar cells with amorphous silicon passivating hole contacts
摘要： Organic photovoltaics (OPVs) consisting of a wide bandgap polymer donor and a nonfullerene acceptor (NFA) have received attention because they can effectively overcome the weaknesses of efficiency and stability for fullerene-based OPVs. One of the NFAs, ITIC, shows an excellent power conversion efficiency, as well as controllable solubility, absorption, crystallinity, and energy level. Thus, high-efficiency OPVs could be achieved by developing polymer donors appropriate for use with ITIC-based OPVs. In this study, the synthesized polymer donor, PBDTT-8ttTPD, containing alkylthieno[3,2-b]thiophene as π-bridge and thieno[3,4-c]pyrrole-4,6(5H)-dione (ttTPD) shows strong absorption with a sharp peak edge at around 700 nm. In addition, the high hole mobility and face-on oriented polymer structures in the blend films make ttTPD the best candidate for the donor in NFA-based OPVs. Notably, the molecular weight of the face-on preferred polymer donor is crucial for determining the power conversion efficiency (PCE) of the NFA-based devices. A high molecular weight improves the π?π stacking ordering, absorption, and nanomorphology of the blend films, resulting in a dramatic PCE improvement from 5.76% to 11.05% compared with that of the fullerene-based OPV device (7.86%).
关键词： organic photovoltaics,nonfullerene acceptors,molecular weight,TPD-based polymer,wide band gap donnor polymer
更新于2025-09-19 17:13:59
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A Review on Energy Band‐Gap Engineering for Perovskite Photovoltaics
摘要： Metal halide perovskites are attractive for highly efficient solar cells. As most perovskites suffer large or indirect bandgap compared with the ideal bandgap range for single-junction solar cells, bandgap engineering has received tremendous attention in terms of tailoring perovskite band structure, which plays a key role in light harvesting and conversion. In this Review, various reported bandgap engineering strategies are summarized. The recently widely used two main strategies including impurity and pressure as well as their underlying mechanisms are reviewed comprehensively. In addition, intermediate band and external electric field for bandgap engineering are also investigated. Moreover, future research directions are outlined to guide the further investigation.
关键词： band-gap engineering,pressure,photovoltaics,impurity alloy,perovskites
更新于2025-09-19 17:13:59
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Light controlled (super) cascode, LC(S)C, a power device with optical turn-on and -off
摘要： The proposed light-controlled cascode is a power electronic device (or circuitry) which can be turned-on and -o? by optical excitation. In contrast to the light-triggered thyristor, which can optically be turned-on but not -o?, the proposed device allows optical turn-on and -o?. Also, it allows a scalability of the blocking voltage by the extension to a light-controlled supercascode [1] which is also shown. After a brief theoretical consideration experimental set-ups will be presented and measurements are shown. Due to the di?culty to buy appropriate devices required for the experimental set-ups some compromises were necessary. Therefore, these ?rst experiments show a very slow switching behaviour. However, this could become speeded up by an optimized photodiode made from wide band gap semiconductor material. In spite of these compromises pulses with a power of 1 kW were turned-on and – o? by the experimental set-up. However, this device is far away from being ready for series production but the feasibility is demonstrated and the potentials are shown.
关键词： optical isolation,wide band gap,supercascode
更新于2025-09-19 17:13:59
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Optimization of Zn Concentration in Chemically Deposited (Cdx-Zn1-x)S Nanocrystalline Films for Solar Cell Applications
摘要： Optimization of Zn Concentration in Chemically Deposited (Cdx-Zn1-x)S Nanocrystalline Films for Solar Cell Applications. An attempt has been made to optimize the Zn concentration in chemically deposited (Cdx-Zn1-x)S (x = 0.2, 0.4, 0.6, 0.8) films on ITO substrate by varying the Cd/Zn composition ratio to enable them to absorb a sizable fraction of solar photons. The phase purity and nano-crystalline character of as-deposited films are established by XRD. Lattice parameters and band-gap values are found to change almost linearly with Cd/Zn composition ratio. The surface morphology supports the nano-crystalline nature of deposited films. The Eg values for (Cdx-Zn1-x)S nanocrystalline films estimated from absorption spectra and corresponding Tauc’s plots range from 2.63 eV to 2.81 eV. The optical behavior in terms of absorption and PL spectra suggests that these films are suitable for application in photovoltaic devices. The electrical resistivity of different (Cdx-Zn1-x)S films has been measured as a function of Zn concentration. The efficiency of resultant CdTe/(Cdx-Zn1-x)S cell is calculated to be approximately 11%.
关键词： Nanocrystalline films,CBD,(Cdx-Zn1-x)S /ITO,solar cell,wide band-gap,window material
更新于2025-09-19 17:13:59
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Structural and spectroscopic studies on the concentration dependent erbium doped lithium bismuth boro tellurite glasses for optical fiber applications
摘要： High gain and better optical properties are the key requirement for the optical fibers and amplifiers to meet the current technological demand. In this regard, in the present investigation, erbium doped lithium bismuth boro tellurite glasses are prepared using melt-quenching technique. The prepared glasses were extensively characterized through, XRD, DSC, UV–Vis-NIR and also Luminescence and Decay techniques to study the concentration dependent structural, optical and luminescence properties. Prepared glasses are amorphous in nature and the corresponding band gap energy decreases with erbium concentration indicates increase of metallicity of the glasses. FTIR studies show different vibration modes majorly borate groups. In addition, Judd-Oflet theory is employed to derive different optical parameters such as intensity parameters, oscillatory strength, branching ratio, stimulated emission cross section and time decay to validate the experimental results of prepared glasses towards optical fiber applications. Estimated values of Stimulated emission, effective band width and gain band width values found higher when compared with other host glasses. Results also show that, 100% branching ratio is obtained for the highest intense peaks corresponds to the transition 4I13/2 → 4I15/2 in NIR luminescence spectra for 1.53 μm broad band. For power dependent 980 nm excitation, up-conversion spectra shows two transitions, namely 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 at 541 and 655 nm corresponds to green and red emission respectively. From the McCumber’s theory, the absorption and emission cross section more comaprable values are obtained for 1 mol% erbium doped glass. About 40% population inversion is obtained with C band from 1500 to 1550 nm. The results suggests that, the prepated glasses are the potential candidates for optical fiber applications.
关键词： Band gap energy,Judd-Oflet,NIR emission,Optical fibers,Boro-tellurite glasses
更新于2025-09-19 17:13:59
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Investigation of Photophysical Properties of Ternary Zn–Ga–S Quantum Dots: Band Gap versus Sub-Band-Gap Excitations and Emissions
摘要： Highly luminescent ternary Zn?Ga?S quantum dots (QDs) were synthesized via a noninjection method by varying Zn/Ga ratios. X-ray diffraction and Raman investigations demonstrate composition-dependent changes with multiple phases including ZnGa2S4, ZnS, and Ga2S3 in all samples. Two distinct excitation pathways were identified from absorption and photoluminescence excitation spectra; among them, one is due to the band-gap transition appearing at around 375 and 395 nm, whereas another one observed nearby 505 nm originates from sub-band-gap defect states. Photoluminescence (PL) spectra of these QDs depict multiple emission noticeable at around 410, 435, 461, and 477 nm arising from crystallographic point defects formed within the band gap. The origin of these defects including zinc interstitials (IZn), zinc vacancies (VZn), sulfur interstitials (IS), sulfur vacancies (VS), and gallium vacancies (VGa) has been discussed in detail by proposing an energy-level diagram. Further, the time-dependent PL decay curve strongly suggests that the tail emission (appear around 477 nm) in these ternary QDs arises due to donor?acceptor pair recombination. This study enables us to understand the PL mechanism in new series of Zn?Ga?S ternary QDs and can be useful for the future utilization of these QDs in photovoltaic and display devices.
关键词： photophysical properties,ternary Zn?Ga?S quantum dots,sub-band-gap defect states,donor?acceptor pair recombination,photoluminescence,band-gap transition
更新于2025-09-16 10:30:52
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Sulfur Alloying Effects on Cu(In,Ga)(S,Se)2 Solar Cell Fabricated by Using Aqueous Spray Pyrolysis
摘要： We fabricated Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells by using aqueous spray based deposition, which is low-cost and advantages in large area deposition. To apply the sprayed film to photo-absorber of solar cell, post sulfo-selenization was carried out. Through the sulfo-selenization process, we were able to fabricate various S-alloyed CIGSSe films from S/(S+Se)=0 (S-0.0) to S/(S+Se)=0.4 (S-0.4). CIGSSe solar cells were made with the S-alloyed CIGSSe absorbers. Power conversion efficiency of CIGSSe solar cell was found to be increased with S-alloying up to S-0.3, and the best efficiency of 10.89 % was obtained with S-0.3 CIGSSe absorber. Comparison study of S-alloyed CIGSSe solar cells showed that enhanced efficiency in S-0.3 solar cell is due to the increased open circuit voltage and improved fill factor, which is induced by S-alloying. In addition, admittance spectroscopy revealed that defect density of deep level was developed in the S-alloyed S-0.3 CIGSSe absorber. But defect density was observed to be rather reduced. Details of characterization and analysis results are discussed in this paper.
关键词： Band Gap Tuning,Spray Pyrolysis,Sulfur Alloying,CIGSSe,Solar Cell
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Electrical, Computer and Communication Technologies (ICECCT) - Coimbatore, India (2019.2.20-2019.2.22)] 2019 IEEE International Conference on Electrical, Computer and Communication Technologies (ICECCT) - Characterisation and performance evaluation of amorphous silicon nitride as passivation layer in thin film aSi:H solar cells
摘要： The fabrication and characterisation of amorphous silicon nitride layer is presented in this paper. The suitability of using it in photovoltaic application has been investigated. It is observed that the band gap of the nitride layers increases with increase in nitrogen content. The experimental results shows that amorphous silicon nitride alloy can be used as passivation layer in devices due to its high optical band gap. On the basis of experimental results, a thin ?lm aSi:H single junction solar cell having aSiNx as passivation layer has been proposed. Further, the behaviour of the proposed structure has been evaluated through simulation using SCAPS1D solar simulator. It is found out that the involvment of amorphous silicon nitride as passivation layer on the top part of the solar cell results in a conversion ef?ciency of 12.9 % and short circuit current density (Jsc) of 15.18 mA/cm2 which are signi?cant values as far as a single junction amorphous silicon thin ?lm solar cell has been considered. Furthermore, a comparison study on solar cell performance parameters of aSi:H solar cell with and without aSiNx passivation layer has been done.
关键词： composition pro?le,optical band gap,FTIR spectrum,passivation layer,PECVD,conversion ef?ciency
更新于2025-09-16 10:30:52
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Mg-Doped ZnO and Zn-Doped MgO Semiconductor Nanoparticles; Synthesis and Catalytic, Optical and Electro-Optical Characterization
摘要： A series of MgxZn1 – xO and ZnxMg1 – xO (mol %) were synthesized by the sol–gel method. All the synthesized nanoparticles were investigated as catalyst in the one-pot, three-component Biginelli condensation reaction of benzaldehyde, ethyl acetoacetate and urea under heterogeneous conditions. Findings revealed Mg0.007Zn0.093O (Zn7) as the best in the mentioned condensation reaction. Zn7 was characterized by FT-IR, SEM, CHN, and XRD. In addition, linear and nonlinear optical properties of MgxZn1 – xO and ZnxMg1 – xO thin films and their colloidal solutions were studied. Using an exact numerical method, some photo-physical properties of the prepared films such as dispersion curve, absorption spectrum, optical permittivity and optical band gap were attained and compared. Finally, using z-scan method at low laser irradiation, thermo-optical effect has also studied and a nonlinear refractive index due to this effect was attained. Doping effect on the optical properties was also investigated physically. It was found in both the particles groups, increasing the doping percent reduces the band gap and it suggests new optoelectronic materials with a spectrum of optical properties.
关键词： z-scan,ZnxMg1 – xO,MgxZn1 – xO,catalyst,optical band gap,nanoparticles,permittivity
更新于2025-09-16 10:30:52