Electrical and photoelectric properties of polycrystalline textured CdTe

The temperature dependences of the resistivity and photoconductivity spectra of polycrystalline coarse-grained stoichiometric CdTe purified in the process of repeated recrystallization at temperatures two times lower than melting point were studied; CdTe ingots were synthesized from starting components subjected profound purification. It is shown that the main characteristics of polycrystals (resistivity, and the lifetime and mobility of carriers) are determined by composite complexes formed as a result of interaction between extended and point defects. The values of the product of mobility multiplied by lifetime are determined.     

Problems of efficiency of photoelectric conversion in thin-film CdS/CdTe solar cells

The available data are generalized and new results of investigation of losses of photoelectric energy conversion in CdS/CdTe thin-film solar cells are reported. The requirements concerning the electrical characteristics of the material, for minimizing the electric losses and providing effective radiation absorption in the active region of the diode structure, are discussed and refined. It is shown to what extent the incomplete collection of photogenerated charge carriers is determined by recombination both at the CdS/CdTe interface (based on the continuity equation taking into account the surface recombination) and in the space-charge region (based on the Hecht equation). The comparison of the calculated and experimental results shows that, in general, both types of recombination losses are important but can be virtually eliminated by the choice of parameters of both the barrier structure and the material used. The limiting values of the short-circuit current density and efficiency of the CdS/CdTe solar cell are discussed.     

Fabrication and photoelectric properties of oxide/CdTe structures

A new technological process is proposed for forming an energy barrier in cadmium telluride crystals, and rectifying photosensitive anisotype and isotype structures are obtained. The photoelectric properties of the obtained structures and their dependence on the geometry of illumination with natural or linearly polarized light were investigated and are discussed. The new technology can be applied to the fabrication of different kinds of photoconversion structures based on cadmium telluride.     

Heterojunction solar cells of SnO2/Si

Heterojunction solar cells (HJSC’s), fabricated by electron beam evaportaion of SnO₂ films onto monocrystalline and polycrystalline Si substrates, show conversion efficiencies as high as 9.9%, fill factors of 0.64, and open circuit voltages of 525 mV under AMI simulated irradiation. The SnO₂, an n-type semiconductor, acts as a transparent window to solar irradiation and as an antireflection coating of the Si, and it provides the band bending in the Si necessary for photovoltaic conversion. The SnO₂ films, nominally 50 nm thick, have conductivities of the order of 10³(Ω-cm)⁻¹ so that the film makes a good electrical contact between the junction and the metallic front contacts. Measurements of C⁻²-V and I-V characteristics are consistent with heterojunction theory, and the data imply an electron affinity of the SnO₂ of approximately 0.8 eV greater than the electron affinity of Si. This value limits the open circuit voltage of HJSC’s made on p-type substrates to values too small for useful photovoltaic conversion. The predominant dark current mechanism of units of n-type substrates at room temperature and forward bias in the range of 0.3−0.5 V is electron-hole recombination in the transition region. The experimentally determined activation energy is 0.51 eV, approximately E_g/2. At forward voltages below 0.3 V, multistep tunneling via interband states predominates. The photocurrent apparently depends on interface states through which the photogenerated holes in the Si recombine with electrons in the SnO₂.     

A novel CdCl2 treatment for glass/SnO2/CBD-CdS/CdTe solar cell

Residual CdCl₂ in chemical bath deposited (CBD) CdS layer was utilized to observe grain growth in CdTe layer for glass/SnO₂/CBD-CdS/CdTe structures. The above as-deposited composite films were subjected to rapid thermal annealing (RTA) for observing grain growth and subsequent cell fabrication. The films were characterized by studying their microstructural and compositional properties. Interfacial mixing behavior was studied by secondary ion mass spectroscopy (SIMS) measurements which showed a slight interfacial diffusion of the CdS layer into the CdTe layer. Performance of a photovoltaic (PV) cell structure with non-optimized thickness of the CdTe and CdS layers obtained by this technique was studied. Carrier life time was obtained from V_oc decay measurement. Photoinduced charge separation observed in this glass/SnO₂/CBD–CdS/CdTe structure was associated with an increase in the dielectric constant and a decrease in the device resistance.     

液相过程制备的CdTe/Al 肖特基纳米晶太阳电池对烧结温度的依赖性研究

本文研究了烧结温度对液相过程制备的碲化镉(CdTe) 纳米晶薄膜性质的影响,以得到最优性能的CdTe/Al 肖特基纳米晶太阳电池。在AM 1.5 条件下,由350℃ 烧结的CdTe 薄膜制作太阳电池得到了2.67% 的最高效率。 当烧结温度增加到350℃ 时,薄膜中纳米晶尺寸明显增加。烧结温度在200℃ 到400℃ 范围内时,短路电流随温度增加而不断增加,但是,过度的烧结 (450℃) 处理会引起太阳电池的短路。     

Effect of window layer composition in Cd1−xZnxS/CdTe solar cells

To improve CdS/CdTe cell/module efficiencies, CdS window layer thinning is commonly applied despite the risk of increased pin‐hole defects and shunting. An alternative approach is to widen the band gap of the window layer (2.42 eV for CdS) via alloying, for example, by forming compositions of Cd_1−xZn_xS. In this study, the performance of Cd_1−xZn_xS/CdTe thin‐film solar cells has been studied as a function of x (from x = 0 to 0.9), widening the window layer band gap up to and over 3.4 eV. Optimum Cd_1−xZn_xS compositions were clearly identified to be around x = 0.7, and limitations to the achievable photocurrent and conversion efficiencies have been addressed. Copyright © 2012 John Wiley & Sons, Ltd.     

Light-induced junction modification in (Cd, Zn)S/CuInSe2solar cells

The current-voltage characteristics of illuminated (Cd, Zn)S/ CuInSe2solar cells are shifted to lower voltages than those expected from the superposition principle. The practical result is a reduced open-circuit voltage,sometimes by as much as 100 mV at room temperature. Dependence of the shift on light intensity, wavelength, temperature, and time after the light, is blocked is investigated. Thermal heating of the junction by the light is discounted in favor of optical excitation of interfacial states. A heterojunction model is proposed for both dark and light conditions. The states trap charge under illumination and approach saturation near 100 mW/cm². The result is a modified effective barrier to carrier transport. Unipolar or dipolar electric charge densities near the interface, the order of 10¹¹cm^-2are sufficient to explain the observed shift of 100 mV. The charging effect is due to a mixture of states in the CuInSe2bandgap which dominate the shift and states in the (Cd, Zn)S which result in a second-order spectral dependence. The relaxation to the equilibrium dark condition indicates that many states with long time constants are involved.     

Electrical and photoelectric properties of anisotype n-TiN/p-Si heterojunctions

Photosensitive n-TiN/p-Si heterojunctions are fabricated by the reactive magnetron sputtering of a thin titanium-nitride film with n-type conductivity onto polished polycrystalline p-Si wafers. The I–V characteristics of the heterostructures are measured at different temperatures. The temperature dependences of the potential-barrier height and series resistance of the n-TiN/p-Si heterojunction are studied. The dominant mechanisms of current transport through the heterojunction in the cases of forward and reverse bias are established. The heterostructures generate the open-circuit voltage V _oc = 0.4 V and the short-circuit current I _sc = 1.36 mA/cm² under illumination with a power density of 80 mW/cm².     

Extraction of optimized parameters for Si0.6Ge0.4 material and SPP mode propagation through Si0.6Ge0.4/Ag/Si0.6Ge0.4 waveguide

The Lorentz model and modified Debye model （MDM） parameters forSi0.6Ge0.4 are presented. A nonlinear optimiza- tion algorithm is developed. The obtained parameters are used to determine the complex relative permittivity of Si0.6Ge0.4, and compared with the experimental data for validation. Finally the obtained parameters are used to analyze the properties of symmetric surface plasmon polariton （SPP） mode propagation in a dielectric-metal-dielectric （DMD） material constructed with silver （Ag） and Si0.6Ge0.4 for further verifying the extracted parameters.     

Electrical and structural properties of epitaxial CdTe/HgCdTe interfaces

In this study, CdTe epilayers were grown by metalorganic chemical vapor deposition on epitaxial HgCdTe with the purpose of developing suitable passivation for HgCdTe photodiodes. Two types of CdTe layers were investigated. One was grown directly,in situ, immediately following the growth of HgCdTe. The second type of CdTe was grown indirectly, on top of previously grown epitaxial HgCdTe samples. In this case, the surface of the HgCdTe was exposed to ambient atmosphere, and a surface cleaning procedure was applied. The material and structural properties of the CdTe/HgCdTe interfaces were investigated using secondary ion mass spectroscopy, Auger electron spectroscopy, Rutherford back scattering, and x-ray double crystal diffractometry techniques. Electrical properties of the CdTe/HgCdTe heterostructure were determined by capacitance-voltage (C-V) characterization of Schottky barrier devices and metal insulator semiconductor devices. Also, a preliminary current-voltage characterization of n⁺ p photodiodes was performed. A theoretical model suitable for analysis of graded heterojunction devices was used for interpretation of C-V measurements.     

Electrical and optical properties of Gen?SnO2 photodetectors

A solid-state photodetector is proposed using an SnO2 transparent layer as a constitutive element in conjunction with a Gen substrate. Special attention is paid to the photo-conductive mode (reverse-biased diode). The electrical characteristics and optical spectral responsivity are reported, noise measurements show a typical contact effect and allow n.e.p. determination. From measured specifications, it appears that, in comparison with commercially available photodiodes, such a structure could be of interest.     

Zn缺位对Ba(Co_(0.6)Zn_(0.4))_(1/3)Nb_(2/3)O_3陶瓷性能的影响

采用传统固相反应法制备了Ba(Co0.58Y0.02Zn0.4-x)1/3Nb2/3O3(x=0,0.01,0.02,0.03,0.04,0.06)陶瓷,系统研究了Zn缺位对陶瓷的物相组成、微观结构和微波介电性能的影响。X线衍射(XRD)结果表明所有配方陶瓷的主晶相均为BaZn0.33Nb0.67O3-Ba3CoNb2O9(BCZN),并存在不同量的第二相Ba8CoNb6O24,适量的Zn缺位可提高BCZN体系的有序度,x=0.02时,其有序度最大。电镜扫描(SEM)结果表明适量的Zn缺位可促进烧结致密化,但Zn缺位过多,会使第二相增多,陶瓷的致密度恶化。随着x的增加,陶瓷的介电常数(εr)基本不变,但品质因数与频率的乘积(Q×f)得到了有效的改善,谐振频率温度系数(τf)先减小后增大。当x=0.02时,BCZN体系陶瓷的εr=35.12,Q×f=52 678GHz,τf=3.28×10-6/℃。     

SnO_2纳米线基场效应晶体管的电学性能研究

基于气-液-固生长机理和原位掺杂技术,成功制备了2%(质量分数)Sb掺杂SnO_2纳米线,所制器件可以在低压环境下工作且不受栅漏电的影响;将该纳米线作为场效应晶体管的沟道,分析了不同比例的Sb掺杂对晶体管电学性能参数的影响。结果显示:Sb质量分数由0.5%增加到2.5%时,随着Sb掺杂量的增大,晶体管的稳定性增强,但栅电压的调控能力减弱,晶体管功耗增大且对空穴和电子的迁移能力减弱。     

Electrical and photoelectric properties of n-CdO-p-InSe anisotype heterojunctions

Anisotype n-CdO-p-InSe heterojunctions are for the first time fabricated on the basis of layered InSe crystals. The temperature dependences of the current-voltage characteristics of the heterojunctions are studied and the mechanisms of charge transport across the barrier under forward and reverse biases are determined. The spectral range of photosensitivity of the heterojunctions is determined.     

Structural mechanisms of optimization of the photoelectric properties of CdS/CdTe thin-film heterostructures

Comparative studies of the effect of chloride treatment of CdS/CdTe thin-film heterostructures on the output characteristics of ITO/CdS/CdTe/Cu/Au solar cells and the crystal structure of their base CdTe layer are carried out. Structural mechanisms determining variation in the efficiency of photoelectric processes in ITO/CdS/CdTe/Cu/Au thin-film solar cells produced by varying the thickness of the CdCl₂ layer during the chloride treatment are suggested. It is shown for the first time by X-ray diffractometry that the metastable hexagonal CdTe phase transforms into a stable cubic modification during the chloride treatment. This circumstance provides a substantial improvement in the photoelectric properties of CdS/CdTe thin-film heterostructures.     

Deposition and doping of CdS/CdTe thin film solar cells

1% oxygen is incorporated into both CdS and CdTe layers through RF sputtering of CdS/CdTe thin film solar cells. The optical and electrical parameters of the oxygenated and O₂-free devices are compared after CdCl₂ treatment and annealing in ambient Ar and/or air. The effects of ambient annealing on the electrical and optical properties of the films are investigated using current-voltage characterization, field emission scanning electron microscopy, X-ray diffraction, and optical transmission spectroscopy. The 1% oxygen content can slightly increase the grain size while the crystallinity does not change. Annealing in ambient Ar can increase the transmission rate of the oxygenated devices.     

(Cd,Co,Nb)掺杂的SnO2压敏材料的电学性质

研究了Cd对(Co，Nb)掺杂SnO2压敏材料电学性质的影响。组分为97．65％SnO2 O．75％Co2O3 0．10％Nb2O5 1．50％CdO的压敏电阻具有最大非线性系数(a=22．2)和最高的势垒(ψB=0．761eV)．当CdO的摩尔分数从0增加到3％时，(Co，Nb)掺杂SnO2压敏电阻的击穿电压从366V／mm增大到556V／mm，1kHz时的相对介电常数从1429减小到1108。晶界势垒高度测量揭示，SnO2的晶粒尺寸的减小是击穿电压增高和介电常数减小的主要原因。对Cd掺杂量增加引起SnO2晶粒减小的根源进行了解释。     

SiO_2掺杂SnO_2-ZnO-Nb_2O_5压敏陶瓷的电学特性

研究了 Si O2 掺杂对 Sn O2 - Zn O- Nb2 O5 压敏陶瓷的影响。实验结果表明 ,Si O2 可以十分显著地影响Sn O2 - Zn O- Nb2 O5 压敏陶瓷的物理和电子性质。掺杂范围为 0 .0 5 %～ 0 .40 % (摩尔分数 )时 ,材料密度在 6.2 1～ 6.5 6g/ cm3之间变动 ,非线性系数在 7.42～ 12 .80之间。烧失率、势垒电压和非线性系数的测量均表明 :掺有x (Si O2 ) =0 .2 %的 Sn O2 - Zn O- Nb2 O5 压敏陶瓷的非线性最好 ,其势垒电压为 0 .67e V,非线性系数达 12 .80     

Efficient CdTe/CdS solar cells and modules by spray processing

Efforts have been directed toward production of efficient, large-area, low-cost photovoltaic modules based on the CdS/CdTe heterojunction, with the objective being to develop an improved materials technology and fabrication process for limited volume production of 1-ft² and 4-ft² CdS/CdTe photovoltaic modules. The present structure of the CdS/CdTe polycrystalline thin-film photovoltaic devices being produced is presented, along with its potential for efficiency improvement. Junction characterization studies are summarized. Module design is described, particularly with regard to encapsulation issue. Future developmental directions are discussed