Photoluminescence study of disordering in the cation sublattice of Cu2ZnSnS4

In this study we investigated the influence of the degree of disordering in the cation sublattice on low temperature photoluminescence (PL) properties of Cu₂ZnSnS₄ (CZTS) polycrystals. The degree of disordering was changed by using different cooling rates after post-annealing at elevated temperatures. The results suggest that in the case of higher degree of cation sublattice disorder radiative recombination involving defect clusters dominates at T = 10 K. These defect clusters induce local band gap energy decrease in CZTS. The concentration of defect clusters can be reduced by giving more time for establishing ordering in the crystal lattice. As a result, radiative recombination mechanism changes and band-to-impurity recombination involving deep acceptor defect with ionization energy of about 200 meV starts to dominate in the low temperature PL spectra of CZTS polycrystals.     

Cd掺杂的Cu_2ZnSnS_4光伏材料的发光光谱及其太阳能电池器件特性

利用溅射-硫化法制备了一系列不同Cd含量掺杂的铜锌锡硫薄膜材料,并获得了转换效率最高达10.65%的薄膜太阳能电池。利用扫描电子显微镜、变温光致发光谱、变激发密度发光光谱对材料进行了表征,分析了电池器件的电容-电压、电流-电压特性。材料的发光峰峰值显示出反常的温度依赖性,载流子表现出强烈的局域化特征。Cd的适当掺入可以抑制较深缺陷的形成并减小发光峰值和带隙值之间的能量差,从而减小了器件开路电压的损失,有利于器件效率的提升。     

Photoluminescence of the layered compound CdInGaS4

Summary The photoluminescence of the layered compound CdInGaS₄ was measured and analysed. The broad emission band at about 1.95 eV was found to be composed of three bands peaking at 2.16, 1.98 and 1.76 eV at 4.8K. These bands are due to free-to-bound or donor-to-acceptor transitions. We have found a new emission band peaking at 2.38 eV. This band shows that peak intensity markedly depends on the position in the crystal and is related to localized centres. The origin of the centres is discussed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Comprehensive loss modeling in Cu2ZnSnS4 solar cells

Thin film solar cells based on Cu₂ZnSnS₄ (CZTS) absorber material suffers from performance issues arising due to the presence of a non-optimal back contact barrier, low carrier lifetime, acceptor/donor point defects in bulk, interface defects at the absorber-buffer junction and grain boundaries within the absorber. We perform comprehensive simulations enumerating the impact of these performance limiting factors on CZTS solar cells. These simulations capture the experimentally observed anomalies in current-voltage (I–V) characteristics and the open-circuit voltage (V_OC) pinning in CZTS solar cells. These cause-effect relationships as elaborated in the findings are expected to be of great interest to the experimentalists working in this field.     

Raman scattering and disorder effect in Cu2ZnSnS4

The Raman spectra of surface regions of bulk Cu₂ZnSnS₄ (CZTS) samples with different Cu and Zn cation content were obtained and the differences in the spectra are attributed to statistical disorder effects in the cation sublattice. This disorder in the Cu and Zn sublattices may initiate a change of the crystal symmetry from kesterite‐type $({I\bar 4})$ to $({I\bar 42m})$ space group. The investigated CZTS crystals grown at high temperature are characterised by the co‐existence of regions with different composition ratio of Cu/(Zn + Sn) which results in kesterite and disordered kesterite phases. The presence of a disordered phase with ${I\bar 42m}$ symmetry is reflected in the appearance of a dominant broadened A‐symmetry peak at lower frequency than the peak of the main A‐symmetry kesterite mode at 337 cm^–1. We suppose that due to a small energy barrier between these phases the transition from one phase to the other can be stimulated by optical excitation of Cu₂ZnSnS₄. The analysis of the Raman spectra measured under different excitation conditions has allowed obtaining first (to our knowledge) experimental evidence of the existence of such optically induced structural transition in CZTS. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopy of defects in irradiated alpo 4 and GaPO 4 crystals

The time-resolved luminescence spectra in energy region of 2.0-6.0 v eV, as well as the excitation spectra (4-35 v eV), reflectivity and the decay kinetics were studied at T =10 v K and 295 v K using selective vacuum ultraviolet excitation in nominally pure crystals as well as crystals with intrinsic defects and radiation defects induced by fast electrons.     

Cu2ZnSnS4类四元硫族半导体的理论研究——以二元、三元、四元半导体的演化为思路

在过去60多年中,人们对半导体的研究集中在一元、二元和三元半导体方面,最近,出于寻找新型廉价、环保、高效光伏转换材料的需要,Cu2ZnSnS4类Ⅰ2-Ⅱ-Ⅳ- Ⅵ4型四元硫族半导体吸引了人们越来越多的关注,它在光催化和热电等多方面的应用也不断被发掘.然而,对于这类四元半导体的基本性质,如晶体结构和电子结构,人们知之甚少,很多研究还停留在经验阶段.文章首先简要回顾了这类半导体的由来和在应用方面的最新进展,然后详细介绍了文章作者对这类四元半导体的第一性原理计算研究工作的进展,其中包括:系统研究了这类硫族半导体在从二元向三元再向四元的演化过程中晶体结构和电子能带结构变化的规律,总结了元素成分对其影响的一般趋势,并结合实验结果分析了这类四元半导体晶格结构表征和带隙测量中易于出现的混淆;文章作者还以Cu2ZnSnS4为例,考察了这类四元化合物相对二元、三元化合物的相稳定性和本征缺陷性质.文章介绍的研究结果将为一系列Ⅰ2-Ⅱ-Ⅳ- Ⅵ4型四元半导体的深入研究提供基础.     

Photoluminescence and luminescence excitation spectra in ZnSiP2

Summary Measurements of photoluminescence and luminescence excitation spectra of ZnSiP₂ have been performed at 4.2K and two results were obtained. One is the observation of a new sharp emission line at 1.980 eV, due to the bound exciton associated with the pseudodirect gap. The other is the observation of another new series of absorption lines in the luminescence excitation spectrum of an emission line, at 1.984 eV, in addition to those reported previously. These results indicate that in ZnSiP₂ radiative transitions occur at both the indirect and the pseudodirect gaps. Paper presented at the ?V International Conference on Ternary and Multinary Compound?, held in Cagliari, September 14–16, 1982.     

Cu2ZnSnS4 类四元硫族半导体的理论研究——以二元、三元、四元半导体的演化为思路

在过去60多年中,人们对半导体的研究集中在一元、二元和三元半导体方面,最近,出于寻找新型廉价、环保、高效光伏转换材料的需要,Cu2ZnSnS4 类 I2-II-IV-VI4型四元硫族半导体吸引了人们越来越多的关注,它在光催化和热电等多方面的应用也不断被发掘. 然而,对于这类四元半导体的基本性质,如晶体结构和电子结构,人们知之甚少,很多研究还停留在经验阶段. 文章首先简要回顾了这类半导体的由来和在应用方面的最新进展,然后详细介绍了文章作者对这类四元半导体的第一性原理计算研究工作的进展,其中包括：系统研究了这类硫族半导体在从二元向三元再向四元的演化过程中晶体结构和电子能带结构变化的规律,总结了元素成分对其影响的一般趋势,并结合实验结果分析了这类四元半导体晶格结构表征和带隙测量中易于出现的混淆;文章作者还以Cu2ZnSnS4 为例,考察了这类四元化合物相对二元、三元化合物的相稳定性和本征缺陷性质. 文章介绍的研究结果将为一系列I2-II-IV-VI4型四元半导体的深入研究提供基础.     

Optically induced structural transformation in disordered kesterite Cu2ZnSnS4

The kesterite-structured semiconductor Cu₂ZnSnS₄ is one of the most promising compound for earth-abundant low-cost solar cells. One of the complex problem on this way deals with its stoichiometry. In this work Raman spectra of Cu-rich Cu₂ZnSnS₄ crystals are discussed in connection with the non-stoichiometric composition and disordering within the cation sublattice of the kesterite. The shift of the main A-peak from 338 to 331 cm^?1 and its broadening are attributed here to transition from the kesterite (I $\bar 4$ symmetry) to the disordered kesterite structure (I $\bar 4$ 2m symmetry). It is shown that this transition may also be driven by an intense light, which could stimulate transformation of Cu⁺-ion to Cu²⁺-ions and facilitates generation of Cu_Zn-defects on 2d-crystalographic positions.     

Enhancement of photosensitivity in bismuth doped Cu2ZnSnS4 thin films

In this paper, the effect of bismuth doping on the structural, morphological, optical and electrical properties of Cu₂ZnSnS₄ (CZTS) films has been investigated. The undoped and bismuth doped CZTS films (0, 0.5, 1, 1.5 and 2 mol%) were deposited on glass substrates by solution based method. The XRD result shows a significant improvement in the crystallinity of the films with increase in bismuth concentration. The Raman spectra of the films show the dominant peak at 334 cm^–1 corresponding to A₁ vibrational mode of CZTS kesterite phase. The FESEM micrographs of the films show an enhancement in the grain size and densification with the addition of bismuth ion concentration. The optical bandgap of the films was found to vary (1.59–1.40 eV) with the doping of bismuth ions. The I –V characteristics indicate twofold increment in the photoconductivity for the bismuth doped CZTS films under 100 mW/cm² illumination suggesting their potential application in photovoltaic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications

First-principles calculations of the band offsets between Cu(2)ZnSnS(4) (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.     

Photoluminescence study of hydrogen donors in ZnO

A photoluminescence study of hydrogenated ZnO bulk crystals is presented. Two excitonic recombination lines at 3362.8 and 3360.1 meV are assigned to hydrogen shallow donors. Experimental evidence is presented that the corresponding donor to the line at 3362.8 meV, previously labeled I₄, originates from hydrogen trapped within the oxygen vacancy, H_O. The line at 3360.1 meV was found to be due to hydrogen located at the bond-centered lattice site, H_BC. The corresponding shallow donor has an ionization energy of 53 meV.     

Significant Enhancement of Hydrogen Production in MoS2/Cu2ZnSnS4 Nanoparticles

Hydrogen produced from water splitting is a renewable and clean energy source. Great efforts have been paid in searching for inexpensive and highly efficient photocatalysts. Here, significant enhancement of hydrogen production has been achieved by introducing ≈1 mol% of MoS₂ to Cu₂ZnSnS₄ nanoparticles. The MoS₂/Cu₂ZnSnS₄ nanoparticles showed a hydrogen evolution rate of ≈0.47 mmol g⁻¹ h⁻¹ in the presence of sacrificial agents, which is 7.8 times that of Cu₂ZnSnS₄ nanoparticles (0.06 mmol g⁻¹ h⁻¹). In addition, the MoS₂/Cu₂ZnSnS₄ nanoparticles exhibited high stability, and only ≈3% of catalytic activity was lost after a long time irradiation (72 h). Microstructure investigation on the MoS₂/Cu₂ZnSnS₄ nanoparticles reveals that the intimate contact between the nanostructured MoS₂ and Cu₂ZnSnS₄ nanoparticles provides an effective one‐way expressway for photogenerated electrons transferring from the conduction band of Cu₂ZnSnS₄ to MoS₂, thus boosting the lifetime of charge carriers, as well as reducing the recombination rate of electrons and holes.     

Photoluminescence of CuGaS2 and heterostructure formation with sputtered ZnS

Summary CuGaS₂ crystals grown by iodine transport exhibit room temperature photoluminescences at 2.45 eV and at 1.44 eV. The spectral distribution of the green emission is shown to be relatively well described by the calculated curve for a direct band-to-band transition withk-selection. The heterojunction formation has been tried between sulfur-treated CuGaS₂ crystals and low-resistivity amorphous ZnS films prepared by sputtering at room temperature. TheI–V characteristic of the diode shows rectifying behaviour, but no injection luminescence has been observed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Effects of sulfur sources on properties of Cu2ZnSnS4 nanoparticles

Three Fe(β-diketonate)₃ compounds namely Fe(tmhd)₃ (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionato), Fe(hfac)₃ (hfac = hexafluoroacetylaceto), and Fe(dbm)₃ (dbm = dibenzoylmethane) were used as substitutes to Fe(acac)₃ (acac = acetyleacetonate) in the synthesis of FePt nanoparticles. The obtained superparamagnetic nanoparticles are 4–5 nm in diameter without showing a large size variation with substituent Fe(β-diketonate)₃. The synchrotron X-ray absorption spectroscopy confirmed the energy dispersive spectroscopy that as-synthesized nanoparticles were composed of iron oxides and metallic FePt₃ alloys. By employing Fe(hfac)₃, the Fe fraction was reduced and the magnetization was modest. The use of Fe(dbm)₃ as starting materials gave rise to densely packed FePt₃/Fe₂O₃ heterodimers. The replacements of Fe(acac)₃ by Fe(tmhd)₃ led to the long-range order of nanoparticle assembly with the narrowest size distribution.     

Photoluminescence and atomic force microscopy studies on pre- and post-irradiated ruby with Fe3+ ion

Photoluminescence spectra measured for pristine ruby and its two irradiated samples with Fe³⁺ ion show R₁, R₂, N lines and a broad band. Decrease in intensities of these features is observed with irradiation of Fe³⁺ ion in ruby. Progressive structural changes and modifications on surface of irradiated rubies with Fe³⁺ ion have been observed by atomic force microscopy. Decrease in intensities is discussed in terms of pair formation.     

溶剂热法制备铜锌锡硫粉末及光学性能研究

以金属氯化物作为金属源,硫脲为硫源,乙二醇为溶剂,聚乙烯吡咯烷酮(PVP)为表面活性剂,采用溶剂热法在较低反应温度下合成了Cu2ZnSnS4(CZTS)粉末。利用X射线衍射仪(XRD)、拉曼光谱(Raman)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)对样品的结构和形貌进行表征。利用紫外-可见光谱(UV-Vis)对样品的光学性能进行研究。结果表明,180℃反应25小时的样品均为锌黄锡矿CZTS颗粒,颗粒形貌为表面花状的微球。当体系中PVP含量为0.2g时,微球尺寸约为2.5μm。当体系中PVP含量为0.3g,0.4g,0.5g时,微球尺寸大约为1.1μm。其中,PVP含量为0.4g的样品分散性较好,在可见区有明显的吸收,用外延法得到其禁带宽度约为1.45eV,与太阳能电池所需的最佳禁带宽度接近。