金属Cr阻挡层对柔性不锈钢衬底Cu(In,Ga)Se2太阳电池性能的影响

研究了Cr扩散阻挡层对柔性不锈钢衬底Cu(InxGa1-x)Se2(CIGS)太阳电池性能的影响.XRD和SEM分析表明,Cr阻挡层能够部分阻挡Fe等杂质从不锈钢衬底热扩散进入CIGS吸收层中,同时可以显著降低CIGS吸收层的粗糙度,提高薄膜结晶质量.从衬底扩散进入吸收层中的Fe元素以FeInSe2的形式存在,并形成FeCu等深能级缺陷,钝化了器件的性能.相同工艺条件下,在玻璃、不锈钢以及不锈钢/Cr阻挡层上所制备电池的(有效面积0.87cm2)转换效率分别为10.7%,7.95%和8.58%,不锈钢衬底电池效率的提高归因于Cr阻挡层的作用.     

Electronic properties of Cu(In,Ga)Se2 solar cells on stainless steel foils without diffusion barrier

Compared with rigid glass, manufacturing of Cu(In,Ga)Se₂ (CIGS) solar cells on flexible stainless steel (SS) substrates has potential to reduce production cost because of the application of roll‐to‐roll processing. Up to now, high‐efficiency cells on SS could only be achieved when the substrate is coated with a barrier layer (e.g. SiO_x or Si₃N₄) for hindering the diffusion of impurities, especially Fe, into the CIGS layer. In this paper, the effect of these impurities on the electronic transport properties of the device is investigated. Using admittance spectroscopy, the presence of a deep defect level at around 320 meV is observed, which deteriorates the efficiency of the solar cells. Furthermore, it is shown that reducing substrate temperature during CIGS deposition is an effective alternative to a barrier layer for reducing diffusion of detrimental Fe impurities into the absorber layer. By applying a CIGS growth process for deposition at low substrate temperatures, an efficiency of 17.7%, certified by Fraunhofer Institute ISE, Freiburg, was achieved on Mo/Ti‐coated SS substrate without an additional metal‐oxide or metal‐nitride impurity diffusion barrier layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Interface Analysis of Cu(In,Ga)Se2 and ZnS Formed Using Sulfur Thermal Cracker

We analyzed the interface characteristics of Zn‐based thin‐film buffer layers formed by a sulfur thermal cracker on a Cu(In,Ga)Se₂ (CIGS) light‐absorber layer. The analyzed Zn‐based thin‐film buffer layers are processed by a proposed method comprising two processes — Zn‐sputtering and cracker‐sulfurization. The processed buffer layers are then suitable to be used in the fabrication of highly efficient CIGS solar cells. Among the various Zn‐based film thicknesses, an 8 nm–thick Zn‐based film shows the highest power conversion efficiency for a solar cell. The band alignment of the buffer/CIGS was investigated by measuring the band‐gap energies and valence band levels across the depth direction. The conduction band difference between the near surface and interface in the buffer layer enables an efficient electron transport across the junction. We found the origin of the energy band structure by observing the chemical states. The fabricated buffer/CIGS layers have a structurally and chemically distinct interface with little elemental inter‐diffusion.     

Controllable Formation of Ordered Vacancy Compound for High Efficiency Solution Processed Cu(In,Ga)Se2 Solar Cells

Solution processing of Cu(In,Ga)Se₂ (CIGS) absorber makes it cost-competitive in the photovoltaic market. It is reported that copper-poor ordered vacancy compound (OVC) is crucial for high performance CIGS solar cells. However, in solution process method, controllable formation of OVC is unavailable and limited research has been carried out. In this work, the controllable formation of the OVC phase on the CIGS surface is successful by controlling the selenization temperature and intentional variation of Cu/(In+Ga) stoichiometry in precursors for top layers and bulk layers deposition. The effects of OVC contents on the device performance are investigated. The CIGS thin film with OVC phase exhibits a lower valence band position. Meanwhile, the CIGS devices with optimized OVC content show decreased interface defects density and better carrier collection ability. The above advantages translate into a champion PCE of 16.39% for CIGS device with OVC phase, which is the champion performance among non-hydrazine solution-processed CIGS solar cells. The results demonstrate that the controllable formation of OVC phase approach should make a significant contribution to the efficiency promoting of solution processed CIGS solar cells.     

Effects of Sb-doping on the grain growth of CIGS thin films fabricated by electrodeposition

Cu(In Ga)Se2(CIGS) solar cells become one of the most important thin film photovoltaic devices thus far. The doping of Sb has improved the grain size of CIGS thin film and therefore led to the enhancement of solar cell efficiency. Various approaches have been used for the Sb doping. Not many reports of electrodeposition of In, Ga and Sb alloy have been reported. In this work, the Sb thin film was coated over Cu film surface prior to the In and Ga deposition in order to form a Cu/Sb/In/Ga metal p...     

Effect of a Mo back contact on Na diffusion in CIGS thin film solar cells

We investigated the effects of the microstructures of molybdenum (Mo) back contacts on sodium (Na) diffusion from sodalime glass into a Cu(In,Ga)Se₂ (CIGS) absorber as a function of the sputter deposition pressure during preparation of the Mo contact layer. The surface characteristics of the Mo layers more significantly affected the diffusion of Na ions into the CIGS compared with the Mo bulk. The Na ion diffusion depended strongly on the amount of oxygen adsorbed onto the Mo layer surfaces. Secondary ion mass spectroscopy results showed that Na accumulated in a layer (Na–O compound) on the Mo surface (the CIGS/Mo interface), and this layer served as a primary source of Na ions diffusing into the CIGS. A trilayered Mo back contact structure was prepared in an effort to decouple the functions of electrical conductance and Na diffusion. The ability of this surface to control the Na concentration in a CIGS absorber is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Cu(In,Ga)Se2太阳电池缓冲层ZnS薄膜性质及应用

在含有ZnSO4,SC(NH2)2,NH4OH的水溶液中采用CBD法沉积ZnS薄膜,XRF和热处理前后的XRD测试表明,ZnS沉积薄膜为立方相结构,薄膜含有非晶态的Zn(OH)2.光学透射谱测试表明,制备的薄膜透过率(λ＞500nm)约为90%,薄膜的禁带宽度约为3.51eV.ZnS薄膜沉积时间对Cu(In,Ga)Se2太阳电池影响显著,当薄膜沉积时间在25～35min时,电池的综合性能最好.对比了不同缓冲层的电池性能,采用CBD-CdS为缓冲层的电池转换效率、填充因子、开路电压稍高于CBD-ZnS为缓冲层的无镉电池,但无镉电池的短路电流密度高于前者,两者转换效率相差2%左右.ZnS可以作为CIGS电池的缓冲层,替代CdS,实现电池的无镉化.     

Improvement of the cell performance in the ZnS/Cu(In,Ga)Se2 solar cells by the sputter deposition of a bilayer ZnO : Al film

ZnS is a candidate to replace CdS as the buffer layer in Cu(In,Ga)Se₂ (CIGS) solar cells for Cd‐free commercial product. However, the resistance of ZnS is too large, and the photoconductivity is too small. Therefore, the thickness of the ZnS should be as thin as possible. However, a CIGS solar cell with a very thin ZnS buffer layer is vulnerable to the sputtering power of the ZnO : Al window layer deposition because of plasma damage. To improve the efficiency of CIGS solar cells with a chemical‐bath‐deposited ZnS buffer layer, the effect of the plasma damage by the sputter deposition of the ZnO : Al window layer should be understood. We have found that the efficiency of a CIGS solar cell consistently decreases with an increase in the sputtering power for the ZnO : Al window layer deposition onto the ZnS buffer layer because of plasma damage. To protect the ZnS/CIGS interface, a bilayer ZnO : Al film was developed. It consists of a 50‐nm‐thick ZnO : Al plasma protection layer deposited at a sputtering power of 50 W and a 100‐nm‐thick ZnO : Al conducting layer deposited at a sputtering power of 200 W. The introduction of a 50‐nm‐thick ZnO : Al layer deposited at 50 W prevented plasma damage by sputtering, resulting in a high open‐circuit voltage, a large fill factor, and shunt resistance. The ZnS/CIGS solar cell with the bilayer ZnO : Al film yielded a cell efficiency of 14.68%. Therefore, the application of bilayer ZnO : Al film to the window layer is suitable for CIGS solar cells with a ZnS buffer layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Solution‐processed Cu(In,Ga)(S,Se)2 absorber yielding a 15.2% efficient solar cell

The remarkable potential for inexpensive upscale of solution processing technologies is expected to enable chalcogenide‐based photovoltaic systems to become more widely adopted to meet worldwide energy needs. Here, we report a thin‐film solar cell with solution‐processed Cu(In,Ga)(S,Se)₂ (CIGS) absorber. The power conversion efficiency of 15.2% is the highest published value for a pure solution deposition technique for any photovoltaic absorber material and is on par with the best nonvacuum‐processed CIGS devices. We compare the performance of our cell with a world champion vacuum‐deposited CIGS cell and perform detailed characterization, such as biased quantum efficiency, temperature‐dependent electrical measurement, time‐resolved photoluminescence, and capacitance spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of MoSe2 on the performance of CIGS solar cells

A CuIn1-xGaxSe2 (CIGS) thin film solar cell model with MoSe2 transition layer was established, using SCAPS-1D software. The influence of MoSe2 interface layer formed between absorption layer CIGS and the back contact Mo on the solar cell performance was investigated.By changing the doping concentration,thickness and bandgap of MoSe2 layer, it is found that the MoSe2 and the variation of parameters have a significant effect on the electrical characteristics and photovoltaic parameters of CIGS thin film solar cells. Based on the energy band, the interfaces of Mo/MoSe2 and MoSe2/CIGS are analyzed. It is considered that Mo/MoSe2 is a Schottky contact, MoSe2/CIGS is an ohmic contact. When suitable parameters of MoSe2 layer are formed into the interface, it will provide a new path for designing CIGS solar cells with thinner absorption layer.     

Modification of deposition process for Cu(In, Ga)Se2 thin film solar cells on polyimide substrate at low temperature

We fabricate polycrystalline Cu(In, Ga)Se₂ (CIGS) film solar cells on polyimide (PI) substrate at temperature of 450 °C with single-stage process, and obtain a poor crystallization of CIGS films with several secondary phases in it. For improving it further, the two-stage process is adopted instead of the single-stage one. An extra Cu-rich CIGS layer with the thickness from 100 nm to 200 nm is grown on the substrate, and then another Cu-poor CIGS film with thickness of 1.5–2.0 μm is deposited on it. With the modification of the evaporation process, the grain size of absorber layer is increased, and the additional secondary phases almost disappear. Accordingly, the overall device performance is improved, and the conversion efficiency is enhanced by about 20%.     

Fabrication and characterization of thin-film Cu (In,Ga) Se2 solar cells on a PET plastic substrate using screen printing

Chalcopyrite copper indium gallium diselenide (CIGS) ink was prepared by dissolving copper, indium, gallium acetylacetonate and Se powder in oleylamine using the hot injection methods. CIGS films were deposited on a PET plastic substrate by a screen-printing technique using CIGS ink with a Ga content ranging from 0.3 to 0.6. X-ray diffraction patterns reveal that the films exhibit a chalcopyrite-type structure. The crystalline grain sizes of the films decrease with increasing Ga content. AFM data shows that the root mean square (RMS) surface roughness of the CIGS film decreases with increasing Ga content. The effects of the Ga content in the CIGS absorber layer on the optical properties of the corresponding thin films and solar cells were studied. The band-gap energies of the CIGS thin films increased with an increasing Ga/(In+Ga) ratio. The short-circuit current (I_SC) of the solar cell decreased linearly with the Ga/(In+Ga) ratio, while the open-circuit voltage (V_OC) increased with this ratio. The solar cell exhibited its highest efficiency of 4.122% at a Ga/(In+Ga) ratio of 0.3.     

KF post deposition treatment in co‐evaporated Cu(In,Ga)Se2 thin film solar cells: Beneficial or detrimental effect induced by the absorber characteristics

Recent breakthroughs in Cu(In,Ga)Se₂ (CIGS) thin film solar cell energy conversion efficiency are related to the application of a potassium fluoride post‐deposition treatment (KF‐PDT) to the completed absorber. Using X‐ray photoelectron spectroscopy and Raman scattering, we compare CIGS layers prior and after the KF‐PDT in the case of a deterioration and an improvement of the solar cells photovoltaic performance. The purpose is to study and model the modification of the surface in both cases and address some of the required characteristics of the absorber, grown on soda lime glass by 3‐stage process, in order to take advantage of the treatment. We show that, in both cases, KF‐PDT induces the formation of GaF₃, which is removed during the subsequent chemical bath deposition of CdS, explaining the Ga depleted absorber surface, already reported in literature. However, the presence or not of an ordered defect compound (ODC), correlated with the third stage duration during the CIGS growth, is shown to be crucial in the modifications of the surface induced by the treatment. When an ODC is present prior the treatment, KF‐PDT leads to the formation of a surface layer of In₂Se₃ containing K, and the photovoltaic performance of completed solar cells are improved. When no ODC is present prior KF‐PDT, no trace of K is found at the absorber surface after the treatment, copper (Cu) segregates into detrimental Cu_xSe phases, high amount of elemental Se is formed, and the photovoltaic performance are lowered. The role of the ODC during the KF‐PDT is finally discussed.     

Theoretical simulation of performances in CIGS thin-film solar cells with cadmium-free buffer layer

Copper indium gallium selenium (CIGS) thin film solar cells have become one of the hottest topics in solar energy due to their high photoelectric transformation efficiency. To real applications, CIGS thin film is covered by the buffer layer and absorption layer. Traditionally, cadmium sulfide (CdS) is inserted into the middle of the window layer (ZnO) and absorption layer (CIGS) as a buffer layer. However, the application of the GIGS/CdS thin film solar cells has been limited because of the environmental pollution resulting from the toxic cadmium atom. Although zinc sulfide (ZnS) has been proposed to be one of the candidates, the performance of such battery cells has not been investigated. Here, in this paper, we systematically study the possibility of using zinc sulfide (ZnS) as a buffer layer. By including the effects of thickness, concentration of a buffer layer, intrinsic layer and the absorbing layer, we find that photoelectric transformation efficiency of ZnO/ZnS(n)/CIGS(i)/CIGS(p) solar cell is about 17.22%, which is qualified as a commercial solar cell. Moreover, we also find that the open-circuit voltage is~0.60 V, the short-circuit current is~36.99 mA/cm² and the filled factor is~77.44%. Therefore, our results suggest that zinc sulfide may be the potential candidate of CdS as a buffer layer.     

Accelerated development of CuSbS2 thin film photovoltaic device prototypes

Development of alternative thin film photovoltaic technologies is an important research topic because of the potential of low‐cost, high‐efficiency solar cells to produce terawatt levels of clean power. However, this development of unexplored yet promising absorbers can be hindered by complications that arise during solar cell fabrication. Here, a high‐throughput combinatorial method is applied to accelerate development of photovoltaic devices, in this case, using the novel CuSbS₂ absorber via a newly developed three‐stage self‐regulated growth process to control absorber purity and orientation. Photovoltaic performance of the absorber, using the typical substrate CuIn_xGa_{1 − x}Se₂ (CIGS) device architecture, is explored as a function of absorber quality and thickness using a variety of back contacts. This study yields CuSbS₂ device prototypes with ~1% conversion efficiency, suggesting that the optimal CuSbS₂ device fabrication parameters and contact selection criteria are quite different than for CIGS, despite the similarity of these two absorbers. The CuSbS₂ device efficiency is at present limited by low short‐circuit current because of bulk recombination related to defects, and a small open‐circuit voltage because of a theoretically predicted cliff‐type conduction band offset between CuSbS₂ and CdS. Overall, these results illustrate both the potential and limits of combinatorial methods to accelerate the development of thin film photovoltaic devices using novel absorbers. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of activation barriers for the diffusion of sodium through CIGS thin‐film solar cells

We have determined the activation energies of sodium diffusion from the soda‐lime glass substrate through the Mo back‐contact layer, as well as through copper indium gallium diselenide (CIGS) deposited on the Mo back‐contact layer of CIGS thin‐film solar cells. The activation energies were determined by X‐ray photoelectron spectroscopy (XPS) to measure surface sodium concentrations before and after thermally induced diffusion. The activation energies were found to be similar for the diffusion of Na through the Mo/glass and CIGS/Mo/glass thin films, approximately 8·6 and 9·6 kcal/mol, respectively. Furthermore, the sodium diffusion was found to occur by annealing in an environment of 1·0×10⁻⁵ Torr of air, oxygen, or water vapor, but not in vacuum of less than 1×10⁻⁸ Torr. In addition, the diffusion of Na was found to occur faster in the presence of oxygen than in water under identical annealing conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of bath temperature on the properties of CuInxGa1-x Se2 thin films grown by the electrodeposition technique

Electrodeposition is a promising and low cost method to synthesize CulnxGa1-xSe2 (CIGS)thin films as an absorber layer for solar cells. The effect of bath temperature on the properties of CIGS thin films was investigated in this paper. CIGS films of 1 μm thickness were electrodeposited potentiostatically from aqueous solution, containing trisodium citrate as a complexing agent, on Mo/glass substrate under a voltage of-0.75 V, and bath temperatures were varied from 20 to 60 ℃. The effects of bath temperature on the properties of CIGS thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy. XRD revealed the presence of the CuIn0.7Ga0.3Se2 phase, the optimal phase for application in solar cells. The grain dimensions and crystallizability increase along with the increase of the bath temperature, and the films become stacked and homogeneous. There were few changes in surface morphology and the composition of the films.     

CIGS薄膜太阳能电池缓冲层CdS薄膜的制备研究

目前CdS材料的制备方法有很多种,但是最常用的是化学水浴法。本文研究了浓度、反应溶液pH值、温度、沉积时间对CdS缓冲层薄膜的影响,对CIGS薄膜太阳能电池缓冲层CdS薄膜的制备方法进行了论述。     

Inkjet printed metallizations for Cu(In1−x Ga x )Se2 photovoltaic cells

This study reports the inkjet printing of Ag front contacts on Aluminum doped Zinc Oxide (AZO)/intrinsic Zinc Oxide (i‐ZnO)/CdS/Cu(In_1−xGa_x)Se₂ (CIGS)/Mo thin film photovoltaic cells. The printed Ag contacts are being developed to replace the currently employed evaporated Ni/Al bi‐layer contacts. Inkjet deposition conditions were optimized to reduce line resistivity and reduce contact resistance to the Al:ZnO layer. Ag lines printed at a substrate temperature of 200°C showed a line resistivity of 2.06 µΩ · cm and a contact resistance to Al:ZnO of 8.2 ± 0.2 mΩ · cm² compared to 6.93 ± 0.3 mΩ · cm² for thermally evaporated contacts. These deposition conditions were used to deposit front contacts onto high quality CIGS thin film photovoltaic cells. The heating required to print the Ag contacts caused the performance to degrade compared to similar devices with evaporated Ni/Al contacts that were not heated. Devices with inkjet printed contacts showed 11.4% conversion efficiency compared to 14.8% with evaporated contacts. Strategies to minimize heating, which is detrimental for efficiency, during inkjet printing are proposed. Copyright © 2011 John Wiley & Sons, Ltd.     

Growth of Cu(In,Ga)Se2 thin films by a novel single‐stage route based on pulsed electron deposition

We report a novel route for growing Cu(In,Ga)Se₂ (CIGS) thin films, based upon the Pulsed Electron Deposition (PED) technique. Unlike other well‐known deposition techniques, PED process allows the stoichiometric deposition of CIGS layers in a single stage, without requiring any further treatments for Cu/(In + Ga) ratio adjustment nor selenization. The structural properties of polycrystalline CIGS films strongly depend on the growth temperature, whereas post‐deposition annealing enhances the grain size and the <112> out‐of‐plane preferred orientation of the chalcopyrite structure, without affecting the film composition. Preliminary measurements of the performances of solar cells based on these films confirm the great potentiality of PED‐grown CIGS as absorber layers. Copyright © 2011 John Wiley & Sons, Ltd.