用光电子能谱研究CdTe太阳电池的背接触特性

CdTe太阳电池的背电极须采用高功函数金属。通过采用光电子能谱(XPS)分析了高功函数金属Au和Ni分别作为背电极的CdTe太阳电池背接触特性,发现在背电极剥离后,Au在ZnTe/ZnTe∶Cu背接触层表面以Au单质形式存在,扩散深度较浅;Ni扩散到ZnTe/ZnTe∶Cu复合层的深度比Au大,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。在两样品中还发现,不论是Te的峰还是Zn的峰,其峰的位移变化都很小,说明两样品中Te和Zn的存在形式没有发生变化。     

CdTe薄膜太阳电池背接触的研究

用近空间升华法制备了CdTe多晶薄膜，用硝酸-磷酸(NP)混合液对薄膜表面进行了腐蚀.经SEM观测，腐蚀后的CdTe薄膜晶界变宽，XRD测试发现，经NP腐蚀后，在CdTe薄膜表面生成了一层高电导的富Te层.在腐蚀后的CdTe薄膜上分别制备了Cu，Cu/ZnTe：Cu，ZnTe：Cu，ZnTe/ZnTe：Cu四种背接触层，比较了它们对太阳电池性能的影响.结果表明，用ZnTe/ZnTe：Cu复合层作为背接触层的效果较好，获得了面积为0.5cm²，转换效率为13.38%的CdTe多晶薄膜太 关键词： 硝磷酸腐蚀 背接触层 CdTe太阳电池     

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.     

新型硒化锑薄膜太阳电池背接触优化

硒化锑(Sb₂Se₃)具有低毒、原材料丰富和光电性能优异等优点,被认为是最具有发展潜力的薄膜太阳电池光吸收层材料之一.但目前Sb₂Se₃薄膜太阳电池光电转换效率与碲化镉、铜铟镓硒和钙钛矿等太阳电池相比仍存在较大差距.限制Sb₂Se₃薄膜太阳电池光电转换效率进一步提升的关键因素之一是,太阳电池结构中Mo背电极和Sb₂Se₃薄膜构建的背接触界面处容易形成较高的势垒,降低载流子的抽取效率.本工作则对Mo背电极进行热处理生成缓冲层MoO₂薄膜,发现缓冲层MoO₂的引入,可有效地促进Sb₂Se₃薄膜的择优取向生长,同时实现太阳电池Mo/MoO2/Sb₂Se₃背接触势垒降低,相应的填充因子、开路电压和短路电流密度均获得显著提高,构建的太阳电池光电转换效率从5.04%提升至7.05%.     

CdTe太阳电池中起因于Cu的深能级

在CdTe太阳电池中,易引入并形成Cu深能级中心. 本文采用深能级瞬态谱测试法研究了ZnTe背接触和石墨背接触CdTe太阳电池的部分深能级中心. 研究中运用密度泛函相关理论,分析闪锌矿结构CdTe,Cd空位体系和掺Cu体系的电子态密度,计算得出T_d场和C_3v场下Cu²⁺ d轨道的分裂情况. 计算结果表明,CdTe太阳电池中的E_v+0206 eV和E_v+0122 eV两个深中心来源于Cu替代Cd原子. 计算结果还表明,掺入Cu可降低CdTe体系能量. 关键词： 深能级瞬态谱 第一性原理 CdTe Cu杂质     

沉积条件对ZnTe/ZnTe:Cu薄膜结构及CdTe电池性能的影响

用共蒸发法沉积了ZnTe/ZnTe:Cu复合多晶薄膜,通过XRD,XPS,C-V,I-V等研究了沉积温度对薄膜结构、Cu浓度分布及电池性能的影响.结果表明,沉积温度对薄膜的结构影响不明显,薄膜呈立方相,经185 ℃退火后出现了六方相.对薄膜的剖析发现,Cu浓度分布呈现先上升到一极大值而后快速下降的趋势, 100 ℃沉积的ZnTe/ZnTe:Cu薄膜,ZnTe层起到了阻止Cu扩散作用,用这种薄膜制作的太阳电池X_D较大 关键词： ZnTe多晶薄膜 沉积温度 薄膜结构 器件性能     

稀土掺杂CdTe太阳电池背接触层ZnTe的第一性原理研究

结合CdS/CdTe太阳电池背接触层的制备要求考虑, 利用基于密度泛函理论平面波超软赝势方法和广义梯度近似, 计算了未掺杂ZnTe、稀土Y、Gd掺杂ZnTe的能带和电子态密度, 得到了不同体系下系统总能和晶格常数. 研究表明, 稀土Y和Gd掺杂后ZnTe结构的稳定性均提高, 掺杂Y使ZnTe与CdTe的晶格匹配更好. 计算表明, 掺杂可使载流子发生简并, 掺Y比掺Gd电子有效质量小, 掺Y与掺Gd的载流子浓度数量级相同. 根据计算结果分析了稀土掺杂对ZnTe背接触层的影响. 关键词： ZnTe 稀土掺杂 第一性原理 太阳电池背接触层     

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AMl.5标准光源下高达14.6％的CdTe电池转换效率.     

模拟分析少子复合速率及吸收层对HIT太阳电池性能的影响

采用AMPS-1D程序模拟分析了前后接触少子复合速率以及吸收层的厚度和少子迁移率对非晶硅/单晶硅异质结太阳电池光伏性能的影响.模拟发现,与太阳电池的前接触少子复合速率相比,背接触少子复合速率对太阳电池光伏性能的影响更为显著.吸收层单晶硅的厚度对太阳电池光伏性能的影响要受到单晶硅隙间缺陷态密度以及背接触少子复合速率的制约.当背接触复合占主要地位时,吸收层越厚电池的转换效率越高;当吸收层隙间缺陷复合占主要地位时,电池的转换效率在某一厚度处达到峰值.吸收层的少子迁移率对太阳电池性能的影响,也要受到背接触少子复合速率的制约.当背接触复合速率较低时,少子迁移率越大,电池的转换效率越高;当背接触复合速率较高时,少子迁移率越小,电池的转换效率越高.     

模拟分析少子复合速率及吸收层对HIT太阳电池性能的影响

采用AMPS-1D程序模拟分析了前后接触少子复合速率以及吸收层的厚度和少子迁移率对非晶硅/单晶硅异质结太阳电池光伏性能的影响.模拟发现,与太阳电池的前接触少子复合速率相比,背接触少子复合速率对太阳电池光伏性能的影响更为显著.吸收层单晶硅的厚度对太阳电池光伏性能的影响要受到单晶硅隙间缺陷态密度以及背接触少子复合速率的制约.当背接触复合占主要地位时,吸收层越厚电池的转换效率越高;当吸收层隙间缺陷复合占主要地位时,电池的转换效率在某一厚度处达到峰值.吸收层的少子迁移率对太阳电池性能的影响,也要受到背接触少子复合速率的制约.当背接触复合速率较低时,少子迁移率越大,电池的转换效率越高;当背接触复合速率较高时,少子迁移率越小,电池的转换效率越高.     

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.     

Development of ZnTe film with high copper doping efficiency for solar cells

Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which reduces the valence band discontinuity and can be used as the electron back reflection layer to inhibit interface recombination. The conductivity of ZnTe:Cu film is improved by applying RF-coupled DC sputtering and post-deposition heat treatment. The doping efficiency is computed as the ratio of free hole density and copper concentration, which can be correlated with performance for CdTe-based solar cell. The higher doping efficiency means that more copper atoms substitute for Zn sites in ZnTe lattices and less mobilized copper atoms remain which can enter into the CdTe absorber layer. Copper atoms are suspected as dominant element for CdTe-based cell degradation. After optimizing the ZnTe:Cu films, a systematic study is carried out to incorporate ZnTe:Cu film into CdTe solar cell. The EQE spectrum is kept relatively stable over the long wavelength range without decreasing. It is proved that the conduction band barrier of device with ZnTe:Cu/Au contact material has an effect on the EQE response, which works as free electron barrier and reduces the recombination rate of free carrier. According to the dark J—V data or the light J—V data in the linear region, the current indicates that the intercept gives the diode reverse saturation current. The results of ideality factor indicate that the dominant recombination occurs in the space charge region. In addition, the space charge density and depletion width of solar cell can be estimated by C—V profiling.     

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.     

Optical properties of Cd1−xZnxTe thin films fabricated through sputtering of compound semiconductors

Cd_1−xZn_xTe thin film fabrication is necessary for its photovoltaic and imaging applications in large scale. Thermally annealed and thereby interdiffused r.f. sputtered multilayers comprising of CdTe and ZnTe have been utilized here for the fabrication of Cd_1−xZn_xTe thin films. Photoluminescence and change of resistance of the multilayer under illumination were studied using different annealing temperatures and varying number of repetitions. It was found that three number of repetitions annealed at 300 °C exhibited the best results.     

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.