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%.     

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.     

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。     

Degradation analysis of thin film photovoltaic modules

Five thin film photovoltaic modules were deployed outdoors under open circuit conditions after a thorough indoor evaluation. Two technology types were investigated: amorphous silicon (a-Si:H) and copper indium gallium diselenide (CIGS). Two 14 W a-Si:H modules, labelled Si-1 and Si-2, were investigated. Both exhibited degradation, initially due to the well-known light-induced degradation described by Staebler and Wronski [Applied Physics Letters 31 (4) (1977) 292], and thereafter due to other degradation modes such as cell degradation. The various degradation modes contributing to the degradation of the a-Si:H modules will be discussed. The initial maximum power output (P_MAX) of Si-1 was 9.92 W, with the initial light-induced degradation for Si-1 ∼30% and a total degradation of ∼42%. For Si-2 the initial P_MAX was 7.93 W, with initial light-induced degradation of ∼10% and a total degradation of ∼17%. Three CIGS modules were investigated: two 20 W modules labelled CIGS-1 and CIGS-2, and a 40 W module labelled CIGS-3. CIGS-2 exhibited stable performance while CIGS-1 and CIGS-3 exhibited degradation. CIGS is known to be stable over long periods of time, and thus the possible reasons for the degradation of the two modules are discussed.     

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     

The In2O3/CdTe interface: A possible contact for thin film solar cells?

Transparent conductive In₂O₃ films were deposited by reactive evaporation of In and analyzed in-situ with photoelectron spectroscopy. The interface formation of In₂O₃ with evaporated CdTe has been investigated using the same technique. A valence band offset ΔE_VB=2.1±0.1 eV is determined, resulting in a negligible conduction band offset. However, In₂O₃ will not provide an Ohmic contact to n-CdTe, due to the Fermi level position at the interface.     

Synthesis of the wheat-like CdSe/CdTe thin film heterojunction and their photovoltaic applications

We report on the fabrication of wheat-like CdSe/CdTe thin film heterojunction solar cells made using a simple electrochemical deposition method and close-spaced sublimation technology on indium tin oxide (ITO) substrates. Structural, optical, and electrical properties of the wheat-like CdSe/CdTe thin film junctions were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS), ultraviolet–visible (UV–vis) absorption spectrum and Keithley 2400 analysis. A significant red-shift of the absorption edge is observed in this heterojunction. The heterostructure is composed of the wheat-like CdSe array and CdTe thin film, showing optical properties typical of type II heterostructures that are suited for photovoltaic applications. A photocurrent density of 8.34 mA/cm² has been obtained under visible light illumination of 100 mW/cm². This study demonstrates that the electrochemical deposition and the close-spaced sublimation technology, which are easily adapted to other chemical systems, are promising techniques for large-scale fabrication of low-cost heterojunction solar cells.     

The role of CdCl2 treatments and annealing in the formation of sintered CdTe nanocrystal solar cells

Solution processing of CdTe nanocrystals is a promising approach for the fabrication of low cost photovoltaic devices at low process temperatures. However despite the inherent advantages of this approach, the nanoscale physical mechanisms underlying the fabrication process are not well understood. Here we demonstrate that chemical treatment of CdTe nanoparticles leads to the production of a deep valence band edge. However, the removal of ligands also introduces sizable quantities of excess oxygen into the films in the form of TeO₂, as proved by XPS. Thermal annealing of the CdTe films in air removes this excess oxygen and the TeO₂ signal. Annealing further increases the energy of the valence band edge, decreases the energy of the conduction band edge, and is responsible for the p-type conductivity observed in NC CdTe films resulting in enhanced photovoltaic performance. Importantly, the presence of oxygen during the annealing step is crucial because it leads to an increase in hole concentrations needed for high performance devices.     

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     

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.     

Observation of multiferroic properties in a CdTe:Mn thin film grown by pulsed laser deposition techniques

We report multiferroic properties in a 3% Mn-doped CdTe (CdTe:Mn or CTM) thin film grown in a co-deposition system constituting pulsed laser deposition and radio frequency (RF) sputtering, in which the Mn concentration was tuned by the sputtering rate of Mn. We observed a clear ferroelectric hysteresis loop in the CTM thin film with remanent polarization of 3.5 μC/cm² and ferromagnetism in the film at a temperature lower than the Curie temperature of 15 K. Both features show direct evidence of multiferroics in the CTM thin film.     

Interface photoluminescence of the SnO2:F/CdS:In/CdTe thin film solar cells prepared partially by the spray pyrolysis technique

CdS/CdTe solar cells were built by depositing a 200 nm layer of SnO₂:F on glass substrates by the spray pyrolysis (SP) technique, a 500 nm CdS:In layer by the same technique and a 1–1.5 μm CdTe layer by vacuum evaporation. The cells were CdCl₂ heat-treated in nitrogen atmosphere for 30 min at 350 °C. The photoluminescence (PL) spectra were measured at the CdS/CdTe interface for two cells with different values of the CdTe layer's thickness at the temperature T=60 K. A deconvolution peak fit was performed from which it is found that the peaks are characteristic of the solid solution CdS_xTe_1?x. The parabolic relation that relates the bandgap energy with the composition was used to estimate x, where x is [S]/([Te]+[S]) and [Te], [S] are the concentrations of Te and S atoms, respectively. The results show that the interface is smooth and the change of the bandgap occurs gradually. The solar cell of the thicker CdTe layer showed more interdiffusion at the CdS/CdTe interface and better photovoltaic characteristics.     

Dip coated TiO2 nanostructured thin film: synthesis and application

TiO₂ thin film was fabricated by dip coating method using titanium IV chloride as precursor and sodium carboxymethyl cellulose as thickening as well as capping agent. Structural and morphological features of TiO₂ thin film were characterized by X-ray diffractometer and field emission scanning electron microscope, respectively. Crystallinity of the film was confirmed with high-intensity peak at (101) plane, and its average crystallite size was found to be 28 nm. The ethanol-sensing properties of TiO₂ thin film was studied by the chemiresistive method. Furthermore, various gases were tested in order to verify the selectivity of the sensor. Among the several gases, the fabricated TiO₂ sensor showed very high selectivity towards ethanol at room temperature.     

Investigation of CdS and CdTe thin films and influence of CdCl2 on CdTe/CdS structure

CdTe/CdS heterojunction solar cell structure has been fabricated using simple, easy and low-cost methods. To fabricate this structure, CdS and CdTe thin films are deposited onto FTO-coated conducting glass substrates by chemical bath deposition (CBD) and electrodeposition method, respectively. The optimized growth conditions are chosen for both CdS and CdTe films by investigating the optical, structural and morphological properties of both the as-deposited and annealed films. Optical measurement showed that CdS films have higher transmittance and lower absorbance, and CdTe films have lower transmittance and higher absorbance in the near infrared region. The band gap of CdS films is estimated to lie in the range 2.29–2.41 eV and that of CdTe films is in the range 1.53–1.55 eV. X-ray diffraction (XRD) study reveals that CdS and CdTe films are polycrystalline with preferential orientation of (1 1 1) plane. Scanning electron microscopy (SEM) study reveals that both films are smooth, void-free and uniformly distributed over the surface of the substrate. Fabricated CdTe/CdS structure showed the anticipated rectifying behaviour, and the rectifying behaviour is observed to improve due to CdCl₂ treatment.     

Electron-capture aftereffects: The case of CdCl2

The compound CdCl₂ was investigated by TDPAC searching for aftereffects at¹¹¹Cd probes. In opposition to previous results, we do not find such effects. This confirms that, as previously suggested, the probe must be a non-isovalent impurity in the compound, so that the atomic disturbances following electron-capture persist long enough to produce detectable perturbations in the angular correlation.     

Plasma dynamics and its relationship with thin film properties of CdTe via pulsed laser deposition (PLD)

2 range). From this data, various emitting species were identified at different regions of the expanding plasma. Plasma temperatures were inferred from the continuous broad background. The velocity of one of the emitting species was calculated from time resolved data. The grown films were characterised by AES and XRD. The role of cadmium is shown to be most important considering the relationship between the plasma emission and the resulting film properties. Received: 16 May 1997/Revised version: 29 September 1997     

Er3+注入CdTe薄膜的结构和光电性能研究

采用离子注入技术对近距离升华制备的CdTe薄膜进行Er3+掺杂研究.讨论了不同掺Er3+浓度对CdTe薄膜的结构和光电性能的影响.利用X射线衍射仪、扫描电子显微镜、紫外-可见分光光度计、霍耳效应测试系统和复阻抗分析仪对样品进行测试.结果表明,适当的掺杂量可以改善CdTe薄膜的结晶性能,降低晶界势垒高度,提高其导电性能.在一定掺杂范围内掺Er3+对CdTe薄膜的光能隙影响不大.     

CdTe太阳电池前电极SnO2:F/SnO2复合薄膜性能分析

减薄CdS窗口层是提高CdS/CdTe太阳电池转换效率的有效途径之一,减薄窗口层会对器件造成不利的影响,因此在减薄了的窗口层与前电极之间引入过渡层非常必要.利用反应磁控溅射法在前电极SnO₂:F薄膜衬底上制备未掺杂的SnO₂薄膜形成过渡层,并将其在N₂/O₂=4 ∶1,550 ℃环境进行了30 min热处理,利用原子力显微镜、X射线衍射仪、紫外分光光度计对复合薄膜热处理前后的形貌、结构、光学性能进行了表征,同时分析了复     

MgB2超导薄膜的微波测量

报道了利用蓝宝石介质谐振器技术测量MgB2超导薄膜的微波表面电阻Rs、OK时的穿透深度λ(O)和超导能隙△(O)．λ(O)和△(O)的值是通过先测量样品穿透深度λ(T)的变化量△λ(T)，然后由BCS理论模型拟合△λ（T)的实验数据得到的．测试样品是利用化学气相沉积技术在MgO(111)基片上制备的c轴织构的MgB2超导薄膜，薄膜的超导转变温度和转变宽度分别为38K和0．1K．微波测试结果表明在10K，18GHz下MgB2薄膜的Rs约为100μΩ，可以和高质量的YBCO薄膜的Rs值相比拟；BCS理论拟合得到的MgB2超导薄膜的λ(0)=102nm，△(0)：1．13kTc．