Performance improvement in CdTe solar cells by modifying the CdS/CdTe interface with a Cd treatment

The performance of n-CdS/p-CdTe solar cells is often degraded under light soaking or thermal stress, even though the technology of CdTe solar cells is close to a commercial level. The Cu diffusion from a Cu back contact to a CdS window layer might degrade the cell's performance. To prevent the Cu diffusion, a very-thin intrinsic CdTe layer was introduced at the n-CdS/p-CdTe interface by depositing a very-thin Cd metal layer on the CdS film and converting the Cd metal into intrinsic CdTe during p-CdTe deposition at high temperature. By the Cd treatment on CdS surface, pinholes or voids were eliminated at the CdS/CdTe and the intermixing of Te and S at the interface was much suppressed. The depletion width was much increased and the intensity of LTPL peak was increased. The analysis suggested that an intrinsic CdTe interlayer was formed and the surface recombination rate was suppressed by the intrinsic interlayer. As a result, the short circuit current of the CdTe solar cell was significantly increased due the increased current gain in the blue wavelength region. The thermal stability of the CdTe solar cell was also greatly improved and the Cu diffusion was retarded by the intrinsic CdTe interlayer at the n-CdS/p-CdTe.     

肖特基势垒对CdS/CdTe薄膜电池J-V暗性能的影响

采用数学模拟方法分析了不同背接触势垒高度(φ_b) 对于CdS/CdTe薄膜电池的J-V(电流密度-电压)方程的影响, 得出了势垒高度与roll-over的变化对应关系. 采用相应Cu/Mo背电极的CdS/CdTe薄膜电池在220-300 K的变温J-V曲线的数值分析与理论分析相对照, 分析了背势垒对于J-V曲线拟合参数的影响. 修正了φ_b 与反向饱和电流(J_b0)关系式, 理论与实验符合得非常好. 关键词： CdS/CdTe薄膜 伏安特性 肖特基势垒 roll-over     

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%.     

Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at E_v+0.128~eV, originates from the vacancy of Cd (V_Cd. The electron trap E1, found at E_c-0.178~eV, is considered to be correlated with the interstitial Cu_i⁼ in CdTe.     

不同温度下制备的CdTe薄膜对太阳电池光电性能的影响

在不同温度下用近空间升华法（CSS）制备了CdTe多晶薄膜,结合I-V,C-V特性及深能级瞬态谱研究了不同温度制备的CdTe薄膜对CdS/CdTe太阳电池性能的影响.结果表明,制备温度对电池组件的开路电压影响不大,对短路电流和填充因子有影响,CdTe薄膜的深中心对温度和频率的响应基本一致.580℃制备的样品暗饱和电流密度最小,载流子浓度较高,光电特性较好,而且空穴陷阱浓度较低,深中心复合作用较小.在此研究基础上制备出了面积为300 mm×400 mm 关键词： 制备温度 CdTe薄膜 深能级瞬态谱（DLTS） CdS/CdTe太阳电池     

CdS/CdTe薄膜太阳电池的深能级瞬态谱和光致发光研究

用深能级瞬态谱和光致发光研究了无背接触层的CdS/CdTe薄膜太阳电池的杂质分布和深能级中心.得到了净掺杂浓度在器件中的分布.确定了两个能级位置分别在E_V+0365 eV和E_V+0282 eV的深中心,它们的浓度分别为167×10¹² cm^-3和386×10¹¹ cm^-2,俘获截面分别为143×10^-14cm²和153×10^-16cm².它们来源于以化学杂质形式存在的Au和（或）Te_Cd^-复合体,或与氩氧气氛下沉积CdTe时的氧原子相关. 关键词： 深能级瞬态谱 光致发光 CdS/CdTe太阳电池     

碲化镉薄膜太阳电池中的关键科学问题研究

文章对CdTe薄膜太阳电池中的4个关键科学问题进行了讨论,并对电池器件的性能进行了研究,其中包括高质量硫化镉薄膜、背接触层、CdS/CdTe界面和CdCl2热处理性能的研究。文章作者研究了背电极接触层中Cu掺杂含量对电池性能的影响,通过改变背接触层中Cu的含量,可以改变Cu与Te反应产生的物相成分,从而发现以Cu1.4Te为主导的背接触缓冲层能有效地减少电池I—V 曲线中的“翻转”(roll-over)现象,同时能有效地降低背接触势垒。此外,还研究了CdS/CdTe界面的CdCl2热处理反应,发现当热处理温度高于350℃时,CdS与CdTe之间的互扩散开始发生,此温度对应于CdS由立方相转变为六方相;而在550℃热处理后,S 和Te 互扩散形成的CdSxTe1-x 化合物,其x 值高达11%。通过优化电池制备工艺,获得了在AM1.5标准光源下高达14.6%的CdTe电池转换效率。     

CdTe,核-壳型CdTe/CdS及CdTe/ZnS量子点的合成及表征

在水相中制备了半导体CdTe纳米晶,核 壳型CdTe/CdS和CdTe/ZnS纳米晶（即量子点;QDs）.利用扫描隧道显微镜（STM）和荧光光谱(FS)对合成的纳米晶量子点进行了研究,并且根据FS的数据进行了量子效率的计算.STM的结果表明合成的量子点直径约为3 nm并且分布良好.为了提高量子效率,对Cd2+浓度和Cd2+∶S2－比例等反应条件进行了研究,结果表明随着回流时间的增加,核 壳型量子点CdTe/CdS的量子效率总体上呈下降趋势.CdTe/CdS在pH8.5,Cd2+∶S2－=10∶1（摩尔比）时可获得80.0%的最大量子效率.同时制备了核 壳型量子点CdTe/ZnS,其最大发射波长由551 nm（CdTe）红移到635 nm（CdTe/ZnS）表明量子点的尺寸在增长,但是量子效率下降到14.4%. 当前研究的量子点可适用于生物标记,生物成像,以及基于共振能量转移的生物传感研究.     

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     

CdTe/CdS核壳结构量子点超快载流子动力学

在水相合成CdTe以及CdTe/CdS核壳结构量子点基础上, 利用基于抽运-探测技术的瞬态差分透射技术研究了CdTe量子点以及不同CdS壳层厚度的CdTe/CdS量子点的最低激子能态的超快激发与弛豫动力学. 研究表明:相比于CdTe,CdTe/CdS量子点的电子空穴由于空间分离,其所需的激发时间要长于电子空穴空间重叠态所需要的激发时间.随着壳层厚度的增加, 量子点表面的钝化有效地减少了表面态相关弛豫机理,并延长相对应的弛豫时间.     

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.     

CdTe/CdS太阳电池I-V，C-V特性研究

测量了CdTe太阳电池器件从50kHz至1MHz频率范围的电容-电压特性，计算了吸收层的载流子浓度和空间电荷区的位置，电容-电压特性测试结果出现两个峰，峰特征与测试频率有关，用多结模型进行模拟分析，解释了实验结果.测量了电池从220K至300K的变温暗电流-电压特性，得出电池的反向暗饱和电流密度J₀和二级管理想因子A，分析了J₀，A随测量温度的变化,并讨论了电池器件的电流特性. 关键词： CdTe太阳电池 电流-电压特性 电容-电压特性     

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.     

Electronic properties and deep level transient spectroscopy of CdS/CdTe thin film solar cells

It is well known that preparing temperatures and defects are highly related to deep-level impurities. In our studies, the CdTe polycrystalline films have been prepared at various temperatures by close spaced sublimation (CSS). The different preparing temperature effects on CdS/CdTe solar cells and deep-level impurities have been investigated by I--V and C--V measurements and deep level transient spectroscopy (DLTS). By comparison, less dark saturated current density, higher carrier concentration, and better photovoltaic performance are demonstrated in a 580oC sample. Also there is less deep-level impurity recombination, because the lower hole trap concentration is present in this sample. In addition, three deep levels, E_v+0.341 eV(H4), E_v+0.226 eV(H5) and E_C-0.147 eV(E3), are found in the 580oC sample, and the possible source of deep levels is analysed and discussed.     

ZnS/CdS复合窗口层对CdTe太阳能电池短波光谱响应的影响

采用磁控溅射法制备了ZnS/CdS复合窗口层,并将其应用于CdTe太阳能电池。对所制备薄膜的形貌和结构等进行了研究。测试了具有不同窗口层的CdTe太阳电池的量子效率和光Ⅰ-Ⅴ特性,分析了ZnS薄膜制备条件对CdTe电池器件性能影响;研究了CdS薄膜厚度和ZnS/CdS复合窗口层对短波区透过率以及CdTe太阳电池的光谱响应的影响。着重研究了具有ZnS/CdS复合窗口层的CdTe太阳电池的短波光谱响应。结果表明,CdS窗口层厚度从100 nm减至50 nm后,其对短波区光子透过率平均提高了18.3%,CdTe太阳电池短波区光谱响应平均提高了27.6%。衬底温度250 ℃条件下制备的ZnS晶粒尺寸小于室温下制备的ZnS。具有ZnS/CdS复合窗口层的CdTe电池中,采用衬底温度250 ℃沉积ZnS薄膜来制备窗口层的电池器件,其性能要优于室温下沉积ZnS制备窗口层的电池器件。这说明晶粒尺寸的大小对电子输运有一定影响。在相同厚度CdS的前提下,具有ZnS/CdS复合窗口层的CdTe电池比具有CdS窗口层在短波的光谱响应提高了约2%。这说明ZnS/CdS复合窗口层能够做到减少对短波光子的吸收,从而使更多的光子被CdTe电池的吸收层吸收。     

Short-circuit current improvement in CdTe solar cells by combining a ZnO buffer layer and a solution back contact

Conventional CdTe solar cells have a CdS window layer, in which an absorption loss of photons with more than 2.4 eV occurs through the CdS layer. A thinner CdS layer was applied to enhance light transmission and a ZnO buffer layer with a band gap of 3.3 eV was introduced to suppress shunting through the thinner CdS window layer. A 100-nm thick ZnO layer sputter-deposited at 300 °C had uniform coverage on a transparent conductive oxide (TCO) after a subsequent high-temperature process. The ZnO layer was effective in preventing shunting through the CdS window layer so that the open-circuit voltage and fill factor of the CdTe solar cells were recovered and the short-circuit current was enhanced over that of the conventional CdTe solar cell. In the ZnO/CdS/CdTe configuration, the short-circuit current was further improved throughout the visible wavelength region by replacing the Cu-metal contact with a Cu solution contact. As a result the short-circuit current from 21.7 to 26.1 mA/cm² and the conversion efficiency of the CdTe solar cell increased from 12 to 15% without antireflective coating. Our result indicates that the Cu solution back contact is a critical factor for achieving a higher cell efficiency in addition to ZnO buffer layer.     

碲化镉薄膜太阳能电池电学特性参数分析

用inline方式全部近空间升华方法制备n-CdS/p-CdTe取得了～11%的转换效率(AM1.5). 把其中n-CdS层采用磁控溅射方法取得了～10%的转换效率(AM1.5). 基于其电流密度-电压(J-V)曲线和外量子效率曲线, 分析了其拟合关键参数对于电池性能的影响程度, 并从理论分析上把目前器件性能参数与当今前沿性能参数以及其理论值进行比较, 指出了如何提高电池转换效率(η)的方法: 提高开路电压(V_oc)、短路电流(J_sc)和填充因子(FF). 关键词： 碲化镉电池 电流密度-电压曲线 外量子效率曲线 电学特性     

CdTe太阳电池的不同背电极和背接触层的特性研究

用Ni替代Au来作为CdTe太阳电池的背电极，比较了Ni,Ni/Au,Au/Ni及Au背电极对电池性能的影响.发现Ni作为背电极和ZnTe/ZnTe:Cu复合层接触，电池的开路电压V_oc略有降低，填充因子FF有增有减，变化幅度不大，但因短路电流I_sc有较大的提高，转换效率η平均增长4％.测试了不同背电极的CdTe太阳电池的暗I-V和C-V特性，对背电极剥离后的样品进行了XPS测试分析.结果表明，Ni扩散到ZnTe/ZnTe:Cu复合层的深度比Au多，且大多呈离子态，与ZnTe/ZnTe:Cu复合层中的富Te离子形成Ni_xTe，提高了掺杂浓度，使电池性能获得改善. 关键词： 金属背电极 复合背接触层 转换效率 CdTe太阳电池     

Preparation of water-soluble CdTe/CdS core/shell quantum dots with enhanced photostability

CdTe/CdS core/shell quantum dots (QDs) have been synthesized in an aqueous phase using thioacetamide as a sulfur source. The quantum yield was greatly enhanced by the epitaxial growth of a CdS shell, which was confirmed by X-ray photoelectron spectroscopy (XPS) results. The quantum yield of as-prepared CdTe/CdS core/shell QDs without any post-preparative processing reached 58%. The experimental results illustrate that the QDs with core/shell structure show better photostability than thioglycolic acid (TGA)-capped CdTe QDs. The cyclic voltammograms reveal higher oxidation potentials for CdTe/CdS core/shell QDs than for TGA-capped CdTe QDs, which explains the superior photostability of QDs with a core/shell structure. This enhanced photostability makes these QDs with core/shell structure more suitable for bio-labeling and imaging.