Evaluation of electrical and optical characteristics of ZnO/CdS/CIS thin film solar cell

In this study, device modeling and simulation are conducted to explain the effects of each layer thickness and temperature on the performance of ZnO/CdS/CIS thin film solar cells. Also, the thicknesses of the CIS and CdS absorber layers are considered in this work theoretically and experimentally. The calculations of solar cell performances are based on the solutions of the well-known three coupling equations: the continuity equation for holes and electrons and the Poisson equation. Our simulated results show that the efficiency increases by reducing the CdS thickness. Increasing the CIS thickness can increase the efficiency but it needs more materials. The efficiency is more than 19% for a CIS layer with a thickness of 2 μm. CIS nanoparticles are prepared via the polyol route and purified through centrifugation and precipitation processes.Then nanoparticles are dispersed to obtain stable inks that could be directly used for thin-film deposition via spin coating.We also obtain x-ray diffraction(XRD) peak intensities and absorption spectra for CIS experimentally. Finally, absorption spectra for the CdS window layer in several deposition times are investigated experimentally.     

真空热蒸发制备CdS/ZnS核/壳异质结纳米线

将传统的真空热蒸发镀膜实验加以改进,先以催化剂辅助蒸发制备出CdS纳米线,再将其作为模板,以ZnS为蒸发源物质,二次蒸发包覆ZnS层,成功制备出大量的CdS/ZnS核/壳异质结纳米线.经X射线衍射、X射线能量色散谱、透射电镜分析表明,所得CdS/ZnS异质结纳米线的核心部分为CdS单晶纳米线,外层为ZnS多晶层.本文的实验方法简便易行,所得纳米结构在光电纳米器件领域有一定应用前景.     

化学水浴法制备大面积CdS薄膜及其光伏应用

采用化学水浴法制备了大面积CdS多晶薄膜,研究了薄膜的形貌、结构和光学性质,结果表明,大面积CdS多晶薄膜具有良好的均匀性,通过优化CdS多晶薄膜,制成了不同CdS窗口层厚度的CdTe小面积太阳电池,减薄CdS薄膜可有效提高器件的短路电流,改善器件性能.随后,在面积30cm×40cm的衬底上制备了全面积为993.6cm²的CdTe太阳电池组件,其27个集成单元的电学性质较为均匀,太阳电池组件的光电转换效率8.13%. 关键词： 化学水浴法(CBD) CdS薄膜 CdTe太阳电池 CdTe太阳电池组件     

CdS thin films growth by fast evaporation with substrate rotation

CdS thin films were grown by fast evaporation technique combined with substrate rotation. The source evaporation temperature was maintained at 600 °C and the substrate temperature at 350 °C with background pressure of 1.0 m Torr. The substrates were corning glass 2947 with dimension of 1 in. × 1 in. rotate at 500 rpm during the growth. In order to verify the quality of the CdS films, the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical measurements. The films shown a flat uniformity thickness with growth rate of ∼3.5 nm/s, the orientation was in the cubic-(1 1 1) and hexagonal-(0 0 2) plane in dependence of the growth time, grain size ∼5 nm, roughness uniformity ∼2.7 nm, transmittance in the visible region spectrum ∼80%, energy band gap between 2.39 and 2.42 eV and short circuit photocurrent density (J_SC) losses in the CdS films of 4.7 mA/cm².     

热沉积法制备纳米二硫化钼薄膜及其光电特性研究

以M oS2粉末为原料,以氩气为携载气体,在400～600℃温度范围内利用热蒸发方法在硅衬底表面制备了不同厚度的M oS2薄膜．利用X射线衍射和扫描电子显微镜分析了M oS2薄膜的结构和表面形貌,发现M oS2薄膜由多晶M oS2粒子组成,颗粒均匀,平均纳米颗粒尺寸约为60 nm ．利用紫外可见光光谱仪测量了其吸收特性,发现样品在720 nm附近有很强的吸收．应用霍尔效应和伏安法研究了M oS2/Si样品的接触特性和电子的运输特性,发现该异质结具有良好的整流特性,即正向电压下电流随电压呈指数增长,而在反向偏压下漏电流很小,电子迁移率可达到6．730×102 cm2/（V · s）．实验结果表明MoS2薄膜具有良好的电学特性,可用来制备晶体管和集成电路等器件．     

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15nm)/a-Si:H(10nm)/ epitaxial c-Si(47μm)/epitaxial c-Si(3μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer S d (Sd =PH3 /(PH3 +SiH4 +H2 )) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35mA/cm2 , a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

对超声波作用下的化学浴沉积方法制备CdS薄膜的谱学分析

用化学浴沉积法制备了CdS薄膜 ,并研究了加超声波对CdS薄膜生长过程的影响。利用卢瑟福背散射 ,X 射线粉末衍射和扫描电子显微镜对薄膜的厚度、晶相和表面形貌进行了表征。结果表明施加超声波的作用能有效地改善薄膜的质量 ,制备出均匀、致密的有较好的晶体结构CdS薄膜。同时 ,通过时间的控制可以精确地控制薄膜在 5 0nm左右 ,以满足制备太阳能电池的特殊要求。     

Effect of emitter layer doping concentration on the performance of silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15 nm)/a-Si:H(10 nm)/ epitaxial c-Si(47 μm)/epitaxial c-Si(3 μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot-wire chemical vapour deposition. The effect of the doping concentration of emitter layer S_d (S_d=PH₃/(PH₃+SiH₄+H₂)) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S_d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S_d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm², a fill factor of 63.3%, and a conversion efficiency of 7.9%.     

Enhancing the performance of thin film CdS/PbS photovoltaic solar cells

This work investigates dependence of the short-circuit current density, open-circuit voltage, fill factor and efficiency of a thin film CdS/PbS solar cell on thickness of transparent conductive oxide (TCO) layer, thickness of window layer (CdS), concentration of uncompensated acceptors (width of space-charge region), carrier lifetime in PbS and the reflectivity from metallic back contact. The effect of optical losses, front and rear recombination losses as well as the recombination losses on space-charge region are also considered in this study. As a result, by thinning the front contact layer indium tin oxide from 400 to 100 nm and window layer (CdS) from 200 to 100 nm it is possible to reduce the optical losses from 32 to 20%. The effect of electron lifetime on the internal and external quantum efficiency can be neglected at high width of the space-charge region. The maximum current density of 18.4 mA/cm² is achieved at wide space-charge region (concentration of uncompensated acceptors = 10¹⁵ cm^?3) and the longest lifetime (τ_n = 10^?6 s) where the optical and recombination losses are about 55%. The maximum efficiency of 5.17%, maximum open-circuit voltage of 417 mV and approximately fixed fill factor of 74% are yielded at optimum conditions such as: electron lifetime = 10^?6 s; concentration of uncompensated acceptors = 10¹⁶ cm^?3; thickness of TCO = 100 nm; thickness of CdS = 100 nm; velocity of surface and rear recombination = 10⁷ cm/s and thickness of absorber layer = 3 μm. When the reflectance from the back contact is 100%, the cell parameters improve and the cell efficiency records a value of 6.1% under the above conditions.     

基于氧化镍背接触缓冲层碲化镉薄膜太阳电池的研究

采用电子束蒸发法制备了NiO薄膜,并对其作为碲化镉薄膜太阳电池背接触缓冲层材料进行了相关研究.NiO缓冲层的加入使得碲化镉太阳电池开路电压显著增大.通过X射线光电子能谱测试得到的NiO/CdTe界面能带图表明NiO和CdTe的能带匹配度很好.NiO是宽禁带P型半导体材料,在电池背接触处形成背场,减少了电子在背表面处的复合,从而提高电池开路电压.通过优化NiO薄膜厚度,制备得到转换效率为12.2%、开路电压为789 mV的碲化镉太阳电池.研究证实NiO是用来制备高转换效率、高稳定性碲化镉薄膜太阳电池的一种极有前景的缓冲层材料.     

Spectroscopic analysis of CIGS2/CdS thin film solar cell heterojunctions on stainless steel foil

This paper presents a spectroscopic analysis of the interface between a CuIn_1−xGa_xS₂ (CIGS2) absorber and a CdS buffer layer on stainless steel foil by Auger electron spectroscopy (AES), inverse photoemission spectroscopy (IPES) and photoelectron spectroscopy (PES) such as X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). By combining these spectroscopic techniques, detailed information about the electronic and chemical properties of the CIGS2 surface and the CdS/CIGS2 interface can be obtained. The gallium concentration in CIGS2 films was found to increase continuously towards the Mo back contact. XPS analysis showed the presence of KCO₃ on the surface of CdS, deposited on etched and un-oxidized samples indicating diffusion of potassium. No potassium was observed on oxidized as well as samples having thicker CdS (50 nm) indicating the effectiveness of oxidation and chemical bath deposition (CBD) process in cleaning the sample surface effectively. In addition, investigation of the electronic level alignment at the interface has been carried out by combining PES and IPES. Conduction band offset of −0.45 (±0.15) eV and a valence band offset of −1.06 (±0.15) eV were measured. These unfavorable conditions limit efficiency of CIGS2 thin film solar cells.     

Thermally evaporated CdS/CdTe thin film solar cells: Optimization of CdCl2 evaporation treatment on absorber layer

CdCl₂ treatment is crucial in the fabrication of highly efficient CdS/CdTe thin-film solar cells. This study reports a comprehensive analysis of thermal evaporated CdS/CdTe thin-film solar cells when the CdTe absorber layer is CdCl₂ annealed at temperatures from 340 to 440 °C. Samples were characterized for structural, optical, morphological and electrical properties. The films annealed at 400 °C showed better crystallinity with a cubic zinc blende structure having large grains. Higher refractive index, optical conductivity, and absorption coefficient were recorded for the CdTe films annealed at 400 °C with CdCl₂. Optimum photoactive properties for CdS/CdTe thin-film solar cells were also obtained when samples were annealed at 400 °C for 20 min with CdCl₂, and the best device exhibited V_OC of 668.4 mV, J_SC of 13.6 mA cm⁻², FF of 53.9% and an efficiency of 4.9%.     

一个非晶硅薄膜太阳能电池制备用激光刻线系统

 非晶硅薄膜太阳能电池制备过程中的激光刻线工艺要求刻线宽度在30 μm～50 μm之间,死区范围小于300 μm,刻线深度符合工艺要求。这不仅要求激光器具有较高的光束质量,而且要求光学系统具有较高的成像质量和较宽的焦深。设计了单激光器四分光路的激光刻线系统。采用设计的激光刻线装置,在1 400 mm×1 100 mm×3.2 mm玻璃基板上进行刻线试验,分别得到刻线P1,P2,P3的线宽为35 μm,50 μm和45 μm,死区范围（P1至P3的距离）为287 μm,最终深度分别为0.98 μm,0.24 μm和0.58 μm,刻线宽度和深度均符合薄膜太阳能电池制备工艺要求。     

Effect of CdS deposition temperature for thermally grown Cu(In,Ga)Se2 and two-step chalcogenized Cu(In,Ga)(S,Se)2 absorbers on solar cell performances

CdS buffer layer of varying thickness ranging from 23 to 58 nm deposited at different substrate temperature were prepared as n-type junction partner for thermally grown Cu(In,Ga)Se₂ and two-step chalcogenized Cu(In,Ga)(S,Se)₂ photovoltaic absorber films and the effect of deposition temperature and time on the CdS growth behavior and solar cell performance were evaluated. High deposition temperature resulted in a thicker CdS layer and more importantly lower density and shallower depth of open voids, which attributed to the improved open-circuit voltage and fill factor due to reduced interface recombination. The solar cell efficiency of thermally grown absorber saturated at about 30 nm thickness of CdS, while that of chalcogenized absorber gradually increased with CdS thickness up to 60 nm without significant loss of short-circuit current density.     

Nanocluster n-CdO thin film by sol-gel for solar cell applications

The nanocluster-CdO film was successfully synthesized by sol-gel method using cadmium acetate and 2-metoxyethanol as starting materials and monoethanolamine as a stabilizer. The structural properties of the CdO film were investigated by atomic force microscopy (AFM). AFM results indicate that the CdO film is consisted of nanoclusters with grain size of 75-85 nm. The optical band gap E_g of nanocluster-CdO film was found to be 2.27 eV. The heterostructure, formed from two semiconductor layers having different optical band gaps, p-Si/n-CdO is prepared as a solar cell device. The electrical properties of the device were characterized by current-voltage and capacitance-conductance-voltage methods. The photovoltaic properties of p-Si/n-CdO device have been investigated. The p-Si/n-CdO heterojunction solar cell shows the best values of V_oc = 0.41 and J_sc = 2.19 mA/cm² under AM1.5 illumination. It is evaluated that this work is useful as a basis for the search of nanomaterial CdO and more competitive p-Si/n-CdO based solar cells, despite the fact that V_oc and J_sc are lower than those reported in the literature.     

反应前驱物中n(S)∶n(Cd)对CdS薄膜结构及发光特性的影响

采用化学水浴以CdCl2·H2O、CS( NH2)2、NH4Cl、NH3·H2O和去离子水作为反应前驱物制备CdS纳米晶薄膜.采用扫描电镜( SEM)、X射线衍射(XRD)、透射光谱和稳态荧光光谱,研究了反应前驱物中不同的n(S)∶n(Cd)对所制备的CdS薄膜的形貌、结构和光学性能的影响.结果表明:反应前驱物中n(S...     

Effect of thickness on physical properties of electron beam vacuum evaporated CdZnTe thin films for tandem solar cells

The thickness and physical properties of electron beam vacuum evaporated CdZnTe thin films have been optimized in the present work. The films of thickness 300 nm and 400 nm were deposited on ITO coated glass substrates and subjected to different characterization tools like X-ray diffraction (XRD), UV‐Vis spectrophotometer, source meter and scanning electron microscopy (SEM) to investigate the structural, optical, electrical and surface morphological properties respectively. The XRD results show that the as-deposited CdZnTe thin films have zinc blende cubic structure and polycrystalline in nature with preferred orientation (111). Different structural parameters are also evaluated and discussed. The optical study reveals that the optical transition is found to be direct and energy band gap is decreased for higher thickness. The transmittance is found to increase with thickness and red shift observed which is suitable for CdZnTe films as an absorber layer in tandem solar cells. The current-voltage characteristics of deposited films show linear behavior in both forward and reverse directions as well as the conductivity is increased for higher film thickness. The SEM studies show that the as-deposited CdZnTe thin films are found to be homogeneous, uniform, small circle-shaped grains and free from crystal defects. The experimental results confirm that the film thickness plays an important role to optimize the physical properties of CdZnTe thin films for tandem solar cell applications as an absorber layer.     

Improvement in efficiency of solar cell by removing Cu2－xSe from CIGS film surface

CIGS thin films are deposited by sputtering and selenization. The synthesis of semiconducting polycrystalline thin films and characteristics of devices based on the CIGS absorbing layers are investigated. Their microstructures are characterized by x-ray diffraction and Raman spectroscopy. The results reveal that there exist metallic Cu_2-xSe compounds in CIGS film surfaces and the compounds are thought to be responsible for the degradation of the open circuit voltage of solar cells. The optimization of selenization temperature profile and copper content in the precursor surfaces is studied, concluding that the conversion efficiency may be improved by removing metallic Cu_2-xSe compounds from the surfaces of CIGS thin films.     

Polyethylene glycol-assisted growth of Cu2SnS3 promising absorbers for thin film solar cell applications

In this paper, we report, for the first time, the results of the polyethylene glycol- (PEG) assisted preparation and characterization of high-quality and well-crystallized Cu₂SnS₃ (CTS) thin films obtained using sol–gel spin-coating method and a subsequent annealing in a sulphur atmosphere. Structural, morphological, compositional, electrical and optical investigations were carried out. The X-ray diffraction patterns of the samples proved the polycrystalline nature and preferred crystallization of the films. No peak referring to other binary or ternary phases were detected in the patterns. The intensity of the preferred orientation and crystallite size of the films increased with increasing PEG content. This trend yielded an improvement in photo-transient currents of the PEG-assisted growth of CTS films. The scanning electron microscopy images revealed that the CTS films have continuous, dense and agglomeration-like morphology. Through energy dispersive X-ray spectroscopy studies, it has been deduced that the samples consist of Cu, Sn and S of which atomic percentages were consistent with Cu/Sn and S/metal initial ratios. The agglomerated morphology of the samples has been attributed to increasing PEG content. A remarkable enhancement was observed in photo-transient currents of p-n junction of the produced films along with increasing PEG content. Through resistivity-temperature measurements, three impurity level electrical activation energy values for each film were found. Optical band gap values of the films were estimated via absorbance-wavelength behaviours and decreased with increasing PEG content. It has been revealed that PEG-assisted growth of CTS thin films is a promising way to improve its photovoltaic characteristics.     

微晶硅锗薄膜作为近红外光吸收层在硅基薄膜太阳电池中的应用

采用射频等离子体增强化学气相沉积技术,制备了具有一定晶化率不同Ge含量的氢化微晶硅锗(μcSi1-xGex:H)薄膜.通过Ⅹ射线荧光谱、拉曼光谱、X射线衍射谱、傅里叶红外谱、吸收系数谱和电导率的测试,表征了μc-Si_(1-x)Ge_x:H的材料微结构随Ge含量的演变.研究表明:提高Ge含量可以增强μc-Si_(1-x)Ge_x:H薄膜的吸收系数.将其应用到硅基薄膜太阳电池的本征层中可以有效提高电池的短路电流密度(J_(sc)).特别是在电池厚度较薄或陷光不充分的情况下,长波响应的提高会更为显著.应用ZnO衬底后,在Ge含量分别为9%和27%时,μc-Si_(1-x)Ge_x:H太阳电池的转换效率均超过了7%.最后,将μc-Si_(1-x)Ge_x:H太阳电池应用在双结叠层太阳电池的底电池中,发现μc-Si_(0.73)Ge_(0.27):H底电池在厚度为800 nm时即可得到比1700 nm厚微晶硅(μc-Si:H)底电池更高的长波响应.以上结果体现μc-Si_(1-x)Ge_x:H太阳电池作为高效近红外光吸收层,在硅基薄膜太阳电池中应用的前景.