ZnTe∶Cu薄膜的制备及其性能

用共蒸发法在室温下沉积了ZnTe∶Cu多晶薄膜.刚沉积的不掺Cu的薄膜呈立方相，适度掺Cu时为立方相和六方相的混合相.随着Cu含量的增加，六方相增加，光能隙减小.根据暗电导温度关系，结合XRD和DSC的结果，认为在110℃、170℃开始出现类CuTe、类Cu2Te相以及Cu0、Cu＋离解的结果导致电导温度关系异常，应用这种薄膜作为背接触层获得了转换效率为11.6%，面积为0.52cm2的CdS/CdTe/ZnTe∶Cu太阳电池.     

The structural,optical, and electrical properties of vacuum evaporated Cu-doped ZnTe polycrystalline thin films

We have studied the structural, optical, and electrical properties of thermally evaporated, Cu-doped, ZnTe thin films as a function of Cu concentration and post-deposition annealing temperature. X-ray diffraction measurements showed that the ZnTe films evaporated on room temperature substrates were characterized by an average grain size of 300Å with a (111) preferred orientation. Optical absorption measurements yielded a bandgap of 2.21 eV for undoped ZnTe. A bandgap shrinkage was observed for the Cu-doped films. The dark resistivity of the as-deposited ZnTe decreased by more than three orders of magnitude as the Cu concentration was increased from 4 to 8 at.% and decreased to less than 1 ohm-cm after annealing at 260°C. For films doped with 6–7 at.% Cu, an increase of resistivity was also observed during annealing at 150–200°C. The activation energy of the dark conductivity was measured as a function of Cu concentration and annealing temperature. Hall measurements yielded hole mobility values in the range between 0.1 and 1 cm²/V·s for both as-deposited and annealed films. Solar cells with a CdS/CdTe/ZnTe/metal structure were fabricated using Cudoped ZnTe as a back contact layer on electrodeposited CdTe. Fill factors approaching 0.75 and energy conversion efficiencies as high as 12.1% were obtained.     

Novel Cu Nanowires/Graphene as the Back Contact for CdTe Solar Cells

Cu‐nanowire‐doped graphene (Cu NWs/graphene) is successfully incorporated as the back contact in thin‐film CdTe solar cells. 1D, single‐crystal Cu nanowires (NWs) are prepared by a hydrothermal method at 160 °C and 3D, highly crystalline graphene is obtained by ambient‐pressure CVD at 1000 °C. The Cu NWs/graphene back contact is obtained from fully mixing the Cu nanowires and graphene with poly(vinylidene fluoride) (PVDF) and N‐methyl pyrrolidinone (NMP), and then annealing at 185 °C for solidification. The back contact possesses a high electrical conductivity of 16.7 S cm^?1 and a carrier mobility of 16.2 cm² V^?1 s^?1. The efficiency of solar cells with Cu NWs/graphene achieved is up to 12.1%, higher than that of cells with traditional back contacts using Cu‐particle‐doped graphite (10.5%) or Cu thin films (9.1%). This indicates that the Cu NWs/graphene back contact improves the hole collection ability of CdTe cells due to the percolating network, with the super‐high aspect ratio of the Cu nanowires offering enormous electrical transport routes to connect the individual graphene sheets. The cells with Cu NWs/graphene also exhibit an excellent thermal stability, because they can supply an active Cu diffusion source to form an stable intermediate layer of CuTe between the CdTe layer and the back contact.     

CdTe solar cell in a novel configuration

Polycrystalline thin‐film CdTe/CdS solar cells have been developed in a configuration in which a transparent conducting layer of indium tin oxide (ITO) has been used for the first time as a back electrical contact on p‐CdTe. Solar cells of 7·9% efficiency were developed on SnO_x:F‐coated glass substrates with a low‐temperature (<450°C) high‐vacuum evaporation method. After the CdCl₂ annealing treatment of the CdTe/CdS stack, a bromine methanol solution was used for etching the CdTe surface prior to the ITO deposition. The unique features of this solar cell with both front and back contacts being transparent and conducting are that the cell can be illuminated from either or both sides simultaneously like a ‘bi‐facial’ cell, and it can be used in tandem solar cells. The solar cells with transparent conducting oxide back contact show long‐term stable performance under accelerated test conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Application of copper thiocyanate for high open‐circuit voltages of CdTe solar cells

Copper thiocyanate (CuSCN) has proven to be a low‐cost, efficient hole‐transporting material for the emerging organic–inorganic perovskite solar cells. Herein, we report that CuSCN can also be applied to CdTe thin‐film solar cells to achieve high open‐circuit voltages (V_OCs). By optimizing the thickness of the thermally evaporated CuSCN films, CdTe cells fabricated by close space sublimation in the superstrate configuration have achieved V_OCs as high as 872 mV, which is about 20–25 mV higher than the highest V_OC for the reference cells using the standard Cu/Au back contacts. CuSCN is a wide bandgap p‐type conductor with a conduction band higher than that of CdTe, leading to a conduction band offset that reflects electrons in CdTe, partially explaining the improved V_OCs. However, due to the low conductivity of CuSCN, CdTe cells using CuSCN/Au back contacts exhibited slightly lower fill factors than the cells using Cu/Au back contacts. With optimized CdS:O window layers, the power conversion efficiency of the best CdTe cell, using CuSCN/Au back contact, is 14.7%: slightly lower than that of the best cell (15.2%) using Cu/Au back contact. Copyright © 2015 John Wiley & Sons, Ltd.     

CdTe/CdS thin film solar cells grown in substrate configuration

The ability to grow efficient CdTe/CdS solar cells in substrate configuration would not only allow for the use of non‐transparent and flexible substrates but also enable a better control of junction formation. Yet, the problems of barrier formation at the back contact as well as the formation of a p–n junction with reduced recombination losses have to be solved. In this work, CdTe/CdS solar cells in substrate configuration were developed, and the results on different combinations of back contact materials are presented. The Cu content in the electrical back contact was found to be a crucial parameter for the optimal CdCl₂‐treatment procedure. For Cu‐free cells, two activation treatments were applied, whereas Cu‐containing cells were only treated once after the CdTe deposition. A recrystallization behavior of the CdTe layer upon its activation similar to superstrate configuration was found; however, no CdTe–CdS intermixing could be observed when the layers were treated consecutively. Remarkably high V_OC and fill factor of 768 mV and 68.6%, respectively, were achieved using a combination of MoO₃, Te, and Cu as back contact buffer layer resulting in 11.3% conversion efficiency. With a Cu‐free MoO₃/Te buffer material, a V_OC of 733 mV, a fill factor of 62.3%, and an efficiency of 10.0% were obtained. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of the layer parameters on the performance of the CdTe solar cells

Influence of the layer parameters on the performances of the CdTe solar cells is analyzed by SCAPS-1D. The ZnO:Al film shows a high efficiency than SnO2:F. Moreover, the thinner window layer and lower defect density of CdS films are the factor in the enhancement of the short-circuit current density. As well, to increase the open-circuit voltage, the responsible factors are low defect density of the absorbing layer CdTe and high metal work function. For the low cost of cell production, ultrathin film CdTe cells are used with a back surface field (BSF) between CdTe and back contact, such as PbTe. Further, the simulation results show that the conversion efficiency of 19.28% can be obtained for the cell with 1-μm-thick CdTe, 0.1-μm-thick PbTe and 30-nm-thick CdS.     

Stable CdTe thin film solar cells with a MoOx back‐contact buffer layer

MoO_x thin films were employed as a buffer layer in the back contact of CdTe solar cells. A monograined CdS layer was employed as the window layer to reduce light absorption. The insertion of a MoO_x buffer layer in the back contact greatly reduced the Schottky barrier leading to increased fill factor and open‐circuit voltage. A CdTe solar cell, with an efficiency as high as 14.2%, was fabricated. The use of a MoO_x buffer layer made it possible to fabricate high‐efficient CdTe solar cell with much less Cu in the back contact, thus greatly enhancing the cell stability. Copyright © 2015 John Wiley & Sons, Ltd.     

温度循环下CdS/CdTe太阳电池稳定性的研究

对CdS/CdTe太阳电池在温度循环下的稳定性进行了研究,测定了其I-V特性曲线,并与室温下的电池作了比较.结果表明:经温度循环后电池的转换效率、填充因子和短路电流密度都有不同程度的下降,而用ZnTe作背接触层的电池稳定性有所改善.     

CuxS背接触层制备及在碲化镉薄膜太阳电池中应用研究

本文采用化学水浴法沉积CuxS薄膜,通过改变Cu元素比例研究其对碲化镉电池效率的影响。研究表明化学水浴法沉积的CuxS是非晶的,采用适当退火条件可以使其晶化,随着退火温度的提高,薄膜变得致密且结晶明显。CuxS薄膜厚度对电池性能有很大的影响,结果表明,随着CuxS薄膜厚度增加,电池性能先增加后减少。薄膜厚度为75nm时,CdS/CdTe电池性能最佳,达到了最高转化效率(η)为12.19%,填充因子(FF)为68.82%,开路电压(Voc)为820mV。     

Copper (I) Oxide (Cu2O) based back contact for p‐i‐n CdTe solar cells

In this paper a promising solution for the notorious problem of manufacturing a stable low ohmic back contact of a CdTe thin film superstrate solar cell is presented without using elemental copper. Instead we have used a Cu₂O layer inserted between the CdTe absorber and metal contact (Au). In contrast to the barrier free band alignment gained by using the transitivity rules, XPS measurements show a barrier in the valence band of the Cu₂O layers directly after deposition, which results in a low performing JV curve. The contact can be improved by a short thermal treatment resulting in efficiencies superior to copper based contacts for standard CdS/CdTe hetero junction solar cells prepared on commercial glass/FTO substrates. By replacing the CdS window layer with a CdS:O buffer layer efficiencies of >15% could be achieved. Copyright © 2016 John Wiley & Sons, Ltd.     

CdS/CdTe thin‐film solar cells with Cu‐free transition metal oxide/Au back contacts

Superstrate CdS/CdTe thin‐film solar cells with Cu‐free transition metal oxide (TMO)/Au and Au‐only back contacts have been fabricated. The TMOs include MoO_3‐x, V₂O_5‐x, and WO_3‐x. The incorporation of the TMO buffer layers at the back contacts resulted in significant improvement on open‐circuit voltage (V_OC) as compared with the cells with Cu‐free Au‐only back contacts. Among the cells using TMO buffer layers, the ones with MoO_3‐x buffer layers exhibited the best performance, yielding an efficiency of 14.1% under AM1.5 illumination with V_OC of 815 mV and a fill factor of 67.9%. Though the performance is slightly behind the best reference cell with a Cu/Au back contact fabricated in our lab with V_OC of 844 mV, fill factor of 76.3%, and efficiency of 15.7%, the use of Cu‐free back contacts may lead to improved long‐term cell stability. Copyright © 2013 John Wiley & Sons, Ltd.     

利用碳糊成膜法改进CdTe太阳电池背处理工艺

提出一种新型的制备Cd％太阳电池背接触方法。利用碳糊成膜法,将含Cu、Te的CdCl2浆状悬浊液涂覆在CdTe表面,只进行一次后退火,X射线衍射（XRD）、二次质子谱（SIMS）测试发现,就能同时达到CdCl2后处理的作用、形成CuxTe的缓冲层和降低背接触势垒的目的。实验结果表明。本文方法将传统的CdCl2后处理和形...     

Effects of Na and MoS2 on Cu2ZnSnS4 thin‐film solar cell

Cu₂ZnSnS₄ (CZTS)‐based materials have a useful band gap and a high absorption coefficient; however, their power conversion efficiency is low compared with that of CdTe and Cu(In,Ga)Se₂‐based solar cells. Two of the factors that strongly affect CZTS solar cell characteristics are the MoS₂ layer and the presence of defects. In this study, Mo back‐contact layers were annealed to control MoS₂ layer formation and the Na content in the Mo layer before the absorber precursor layer was deposited. The increase in oxygen content in the Mo layer suppressed MoS₂ layer formation. In addition, the increase in Na diffusion during the initial stage of the absorber precursor deposition decreased the defect density in the absorber layer and in the absorber–buffer interface. These results were verified through measurements of the external quantum efficiency, the temperature dependence of the open‐circuit voltage (V_OC), and admittance spectra. The current densities (J_SC) and V_OC, as well as the power conversion efficiencies, improved as the annealing temperature of the Mo layer increased, which suggests that CZTS solar cell characteristics can be improved by suppressing MoS₂ layer formation and increasing Na content in the Mo layer before deposition of the absorber precursor layer. Copyright © 2014 John Wiley & Sons, Ltd.     

Ultrathin CdTe Solar Cells with MoO3−x /Au Back Contacts

We report on the fabrication and characterization of CdTe thin-film solar cells with Cu-free MoO_3?x /Au back contacts. CdTe solar cells with sputtered CdTe absorbers of thicknesses from 0.5 to 1.75 μm were fabricated on Pilkington SnO₂:F/SnO₂-coated soda–lime glasses coated with a 60- to 80-nm sputtered CdS layer. The MoO_3?x /Au back contact layers were deposited by thermal evaporation. The incorporation of MoO_3?x layer was found to improve the open circuit voltage (V _OC) but reduce the fill factor of the ultrathin CdTe cells. The V _OC was found to increase as the CdTe thickness increased.     

Copper migration in cdte heterojunction solar cells

CdTe solar cells were fabricated by depositing a Au/Cu contact with Cu thickness in the range of 50 to 150Å on polycrystalline CdTe/CdS/SnO₂/glass structures. The increase in Cu thickness improves ohmic contact and reduces series resistance (R_s), but the excess Cu tends to diffuse into CdTe and lower shunt resistance (R_sh) and cell performance. Light I-V and secondary ion mass spectros-copy (SIMS) measurements were performed to understand the correlations between the Cu contact thickness, the extent of Cu incorporation in the CdTe cells, and its impact on the cell performance. The CdTe/CdS/SnO₂/glass, CdTe/ CdS/GaAs, and CdTe/GaAs structures were prepared in an attempt to achieve CdTe films with different degrees of crystallinity and grain size. A large grain polycrystalline CdTe thin film solar cell was obtained for the first time by selective etching the GaAs substrate coupled with the film transfer onto a glass substrate. SIMS measurement showed that poor crystallinity and smaller grain size of the CdTe film promotes Cu diffusion and decreases the cell performance. Therefore, grain boundaries are the main conduits for Cu migration and larger CdTe grain size or alternate method of contact formation can mitigate the adverse effect of Cu and improve the cell performance.     

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.     

Transition resistances of ohmic contacts to p-type cdte and their time-dependent variation

Ohmic contacts to p-type CdTe are important for the development of solar cells based on this semiconductor, as for instance CdS/CdTe or ITO/ CdTe solar cells. Ohmic contacts to CdTe Bridgman crystals, doped with phosphorus, have been examined with respect to their resistivity dependence and their variation as a function of time. The ‘specific’ contact resistance r shows a linear dependence on the bulk resistivity; in addition, it is affected by the oxygen content of the CdTe. The lowest r obtained was 0.07Ω cm. With one exception, ali the contacts with nickel, gold and platinum deposited on different crystals show a more or less pronounced increase of r as a function of time.     

Nickel silicide contacts formed by excimer laser annealing for high efficiency solar cells

Driven by the relatively high cost of silver (Ag), interest has grown in the photovoltaic (PV) industry to substitute conventional screen printed (SP) Ag front contacts with copper (Cu) plated contacts. The approach chosen here applies selective laser ablation of the front anti‐reflection coating (ARC), then forming self‐aligned nickel silicides (NiSi_x) contacts, and thickening the lines by Cu plating to achieve the desired line conductivity. A successful implementation of this scheme requires annealing to form NiSi_x with low contact resistance. However, it has been shown that industrial shallow emitters can be damaged severely upon conventional annealing of nickel. In this paper, we show that by using large area excimer laser annealing (ELA), NiSi_x contacts can be formed on industrial shallow emitters without the associated junction degradation. On the basis of sheet resistance, transmission electron microscopy, and lifetime measurements, we demonstrate that NiSi_x formation by ELA can be achieved in narrow contact openings without damaging the passivation and reflectance properties of the neighboring ARC. In addition, the thresholds for NiSi_x formation for different Ni thicknesses are quantified by rigorous finite element simulations and compared with experimental data. Finally, high efficiency passivated emitter and rear cell type solar cells featuring a shallow 85 Ω/sq emitter have been processed on large area CZ–Si using laser ablation of the ARC and subsequent NiSi_x formation by ELA. These cells show an average efficiency gain of 0.4%_abs compared with cells processed with reference SP contacts. In this work, the best performing cell with the ELA process reached 20.0% energy conversion efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

CdTe p—i—n薄膜太阳能电池热平衡态数值分析

通过应用Ｓｃｈａｒｆｅｔｔｅｒ－Ｇｕｍｍｅｌ解法数值求解Ｐｏｉｓｓｏｎ方程，对热平衡态ｐ（ＺｎＴｅ）／ｉ（ＣｄＴｅ）／ｎ（ＣｄＳ）薄膜太阳能电池进行计算机数值模拟。结果表明，ｐ（ＺｎＴｅ）／ｉ（ＣｄＴｅ）／ｎ（ＣｄＳ）的能带结构有利于光生载流子传输与收集，ＣｄＴｅ中高内建场提高了光生载流子通过有源区的输运能力，对ＣｄＴｅ进行适量Ｐ型掺杂还能提高其电池的短波收集效率。