Cr应力缓释层对柔性Cu_(2)ZnSn(S,Se)_(4)薄膜太阳电池性能的影响

柔性Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)薄膜太阳电池中的应力是阻碍其发展的一大瓶颈。采用磁控溅射法在柔性Ti衬底和Mo背电极之间引入不同厚度的Cr缓释层,研究其对CZTSSe薄膜应力的影响。结果表明,当Cr应力缓释层厚度为80 nm时,薄膜的结晶质量最好,电池具有最佳的光电性能,相比没有Cr应力缓释层存在的情况,薄膜的残余应力从-7.15 GPa降低至-3.61 GPa,电池的光电转换效率(PCE)从2.89%提高至4.65%,增加了60.9%。Cr应力缓释层的引入不会影响CZTSSe薄膜的晶体结构,相反可有效提高薄膜的结晶质量,降低薄膜的残余应力,最终提高电池的光电性能。

硒化对Cu2ZnSn(S,Se)4太阳电池光伏性能影响机制研究

文章利用溶液法和硒化技术在镀Mo钠钙玻璃(Mo/SLG)衬底上制备出具有锌黄锡矿结构的Cu 2ZnSn(S,Se)4(CZTSSe)薄膜,研究了硒化温度(500~600℃)和硒化时间(5~30 min)对CZTSSe薄膜质量和生长在CZTSSe/Mo界面的Mo(S,Se)2(MSSe)过渡层厚度的影响.发现在500~550℃,15~30 min硒化可制备出晶粒质量好、尺寸大、堆积致密的CZTSSe薄膜和厚度合适的MSSe过渡层;以经530℃,5~30 min硒化获得的CZTSSe薄膜为吸收层,制备了结构为Al/ITO/i-ZnO/CdS/CZTSSe/Mo/SLG的太阳电池.发现对应5~15 min硒化的太阳电池的转换效率(PCE)随硒化时间的增加从1.9%增加到7.48%,对应15~30 min硒化的太阳电池的PCE却随硒化时间的增加从7.48%减小到4.23%.PCE的增加归因于开路电压(V oc)、短路电流密度(J sc)和填充因子(FF)的增加,PCE的减小归因于V oc和FF减少;通过研究CZTSSe薄膜质量和MSSe厚度对太阳电池光损失、内建电场和电学参数的影响,阐述了硒化温度和时间对V oc,J sc和FF的影响机制.

Cu_2ZnSn(S,Se)_4薄膜太阳电池研究进展

CdTe和Cu(In,Ga)(S,Se)_2(CIGSSe)光吸收材料在新型化合物半导体太阳电池研究中占据着主导地位。尽管CdTe和CIGS太阳电池拥有较高的转换效率和先进的技术,但是仍存在着一些问题,如所用材料中的元素地壳丰度低或有毒,这阻碍了其未来的大规模应用。近年来,由于Cu_2ZnSn(S,Se)_4(CZTSSe)薄膜太阳电池使用的元素地壳含量丰富且环境友好,逐渐成为了研究的热点。CZTSSe光吸收材料被认为能够取代CdTe和CIGS成为下一代光伏技术的潜力材料。基于此,本文将简单介绍CZTSSe材料的结构、性质和制备方法。重点阐述CZTSSe材料的组装技术和沉积方法的发展和优势,如基于真空的沉积方法和基于溶液的沉积方法,简述其优缺点。此外,本文对CZTSSe组装和CZTSSe纳米晶制备方法的最新研究进展也进行了总结。最后,对CZTSSe光伏技术的一些限制因素进行了分析,并对CZTSSe薄膜电池未来的研究前景进行了展望。

Cu_2ZnSn(S,Se)_4纳米晶薄膜太阳能电池的研究进展

Cu2Zn Sn(S,Se)4(CZTSSe)材料因其光吸收系数高,具有理想的带隙,且所含元素丰度高、无毒等特性,非常适合作为太阳能电池的吸收层材料,有望成为低成本和高性能光伏发电的材料之一,引起广泛的关注.介绍了CZTSSe材料的基本物理性质及其纳米晶的生长机制,重点介绍了热注入方法合成CZTSSe纳米晶的过程,概述了目前CZTSSe纳米晶薄膜太阳能电池的现状,最后探讨了CZTSSe薄膜太阳电池中存在的问题及以后的发展方向.

Cu_2ZnSnS_4 thin films prepared by sulfurization of ion beam sputtered precursor and their electrical and optical properties

Cu2ZnSnS4 (CZTS) thin films were successfully prepared by sulfurization of ion bean sputtered precursors on soda-lime glass substrate. The single phase of stannite-type structure CZTS films were obtained as revealed in EDS and XRD analysis when the ratios of the constituents of CZTS thin films are close to stoichiometric by optimizing the conditions of precursor preparation and sulfurization. A low sheet resistivity as about 0.156 Ω·cm and a high absorption coefficient as 1×104 cm-1 were achieved in this method by Hall effect measurements and UV-VIS spectrophotometer. The optical band-gap energy of the CZTS sample is about 1.51 eV, which is very close to the optimum value for a solar-cell absorber.

Lithium-assisted synergistic engineering of charge transport both in GBs and GI for Ag-substituted Cu2ZnSn(S,Se)4 solar cells

Although silver(Ag) substitution offers several benefits in eliminating bulk defects and facilitating interface type inversion for Cu2ZnSn(S,Se)4(CZTSSe) photovoltaic(PV) technology, its further development is still hindered by the fairly low electrical conductivity due to the significant decrease of acceptors amount.In this work, a versatile Li–Ag co-doping strategy is demonstrated to mitigate the poor electrical conductivity arising from Ag through direct incorporating Li via postdeposition treatment(PDT) on top of the Ag-substituted CZTSSe absorber. Depth characterizations demonstrate that Li incorporation increases ptype carrier concentration, improves the carrier collection within the bulk, reduces the defects energy level as well as inverts the electric field polarity at grain boundaries(GBs) for Ag-substituted CZTSSe system. Benefiting from this lithium-assisted complex engineering of electrical performance both in grain interior(GI) and GBs, the power conversion efficiency(PCE) is finally increased from 9.21% to 10.29%. This systematic study represents an effective way to overcome the challenges encountered in Ag substitution,and these findings support a new aspect that the synergistic effects of double cation dopant will further pave the way for the development of high efficiency kesterite PV technology.

First-principles study on the alkali chalcogenide secondary compounds in Cu(In,Ga)Se_2 and Cu_2ZnSn(S,Se)_4 thin film solar cells

The beneficial effect of the alkali metals such as Na and K on the Cu（In.Ga）Se2 （CIGS） and Cu2ZnSn（S,Se）4 （CZTSSe） solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum （VBM） level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.

Precisely tuning Ge substitution for efficient solution-processed Cu_2ZnSn(S,Se)_4 solar cells

The kesterite Cu2ZnSn（S,Se）4 （CZTSSe） solar cells have yielded a prospective conversion efficiency among all thin- film photovoltaic technology. However, its further development is still hindered by the lower open-circuit voltage （Voc）, and the non-ideal bandgap of the absorber is an important factor affecting this issue. The substitution of Sn with Ge provides a unique ability to engineer the bandgap of the absorber film. Herein, a simple precursor solution approach was successfully developed to fabricate Cu2Zn（SnyGel_y）（SxSe~ x）4 （CZTGSSe） solar cells. By precisely adjusting the Ge content in a small range, the Voc and Jsc are enhanced simultaneously. Benefitting from the optimized bandgap and the maintained spike structure and light absorption, the 10% Ge/（Ge＋Sn） content device with a bandgap of approximately 1.1 eV yields the highest efficiency of 9.36%. This further indicates that a precisely controlled Ge content could further improve the cell performance for efficient CZTGSSe solar cells.

Theoretical study on the kesterite solar cells based on Cu_2ZnSn(S,Se)_4 and related photovoltaic semiconductors

The kesterite thin film solar cells based on the quaternary Cu2ZnSnS4 and Cu2ZnSnSe4 and their alloys Cu2ZnSn（S,Se）4 have been considered as environment-friendly and non-toxic alternatives to the currently commercialized CdTe and Cu（In,Ga）Se2 thin film solar cells. From the theoretical point of view, we will review how the group I2-II-IV-VI4 quaternary compound semiconductors are derived from the binary CdTe and the ternary CuInSe2 or CuGaSe2 through the cation mutation, and how the crystal structure and electronic band structure evolve as the component elements change. The increased structural and chemical freedom in these quaternary semiconductors opens up new possibility for the tailoring of material properties and design of new light-absorber semiconductors. However, the increased freedom also makes the development of high-efficiency solar cells more challenging because much more intrinsic point defects, secondary phases, surfaces, and grain-boundaries can exist in the thin films and influence the photovoltaic performance in a way different from that in the conventional CdTe and Cu（In,Ga）Se2 solar cells. The experimental characterization of the properties of defects, secondary phase, and grain-boundaries is currently not very efficient and direct, especially for these quaternary compounds. First-principles calculations have been successfully used in the past decade for studying these properties. Here we will review the theoretical progress in the study of the mixed-cation and mixed-anion alloys of the group I2-II-IV- VI4 semiconductors, defects, alkaline dopants, and grain boundaries, which provided very important information for the optimization of the kesterite solar cell performance.

Effect of thermal pretreatment of metal precursor on the properties of Cu_2ZnSnS_4 films

Zn/Sn/Cu （CZT） stacks were prepared by RF magnetron sputtering. The stacks were pretreated at different tem- peratures （200℃, 300 ℃, 350 ℃, and 400 ℃） for 0.5 h and then followed by sulfurization at 500℃ for 2 h. Then, the structures, morphologies, and optical properties of the as-obtained Cu2ZnSnS4 （CZTS） films were studied by x-ray diffraction （XRD）, Raman spectroscopy, UV-Vis-NIR, scanning electron microscope （SEM）, and energy-dispersive x-ray spectroscopy （EDX）. The XRD and Raman spectroscopy results indicated that the sample pretreated at 350℃ had no secondary phase and good crystallization. At the same time, SEM confirmed that it had large and dense grains. According to the UV-Vis-NIR spectrum, the sample had an absorption coefficient larger than 10^4 cm-1 in the visible light range and a band gap close to 1.5 eV.

In-doping collaboratively controlling back interface and bulk defects to achieve efficient flexible CZTSSe solar cells

Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface and passivate deep level defects in CZTSSe bulk concurrently for improving the performance of flexible device.The results show that In doping effectively inhibits the formation of secondary phase(Cu(S,Se)_(2))and VSndefects.Further studies demonstrate that the barrier height at the back interface is decreased and the deep level defects(Cu_(Sn)defects)in CZTSSe bulk are passivated.Moreover,the carrier concentration is increased and the V_(OC) deficit(V_(OC,def))is decreased significantly due to In doping.Finally,the flexible CZTSSe solar cell with 10.01%power conversion efficiency(PCE)has been obtained.The synergistic strategy of interface modification and bulk defects passivation through In incorporation provides a new thought for the fabrication of efficient flexible kesterite-based solar cells.

Surface defect ordered Cu_(2)ZnSn(S,Se)_(4) solar cells with efficiency over 12% via manipulating local substitution

The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit(V_(oc,deficit)) and significantly limit kesterite photovoltaics performance,primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered Cu_(Zn) defects and generate benign n-type Zn_(Ag) donors. Taking advantage of the decreased annealing temperature of Ag F post deposition treatment(PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the Ag F-PDT device finally achieves maximum efficiency of 12.34% with enhanced V_(oc) of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.

Na-doping-induced modification of the Cu_(2)ZnSn(S,Se)_(4)/CdS heterojunction towards efficient solar cells

It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple solution method,and then the effects on the surface properties of the absorber layer,the buffer layer growth,and the modifications of the solar cell performance induced by the Na doping are studied.The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping.In addition,the contact angle of the surface increases because of Na doping.As a consequence,the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased.The difference of quasi-Fermi levels(EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell,so that open circuit voltage(VOC) increased significantly.This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.

A feasible and effective solution-processed PCBM electron extraction layer enabling the high VOC and efficient Cu_(2)ZnSn(S, Se)_(4) devices

Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.

Synthesis of Cu_2ZnSnS_4 thin film from mixed solution of Cu_2SnS_3 nanoparticles and Zn ions

The Cu2ZnSnS4 thin film was prepared by a facile solution method without vacuum environment and toxic substance. The formation mechanism of the film was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman scattering measurements. Through cyclic voltammetry and photo-electricity tests, the electrocatalytic activity of the prepared film as the counter electrode of dye-sensitizedsolar cell was also studied. The results show that the mixed precursor solution mainly consists of Cu2SnS3 nanoparticles and Zn ions.After 550 °C annealing process on the precursor film prepared from the mixed solution, Cu2ZnSnS4 thin film is obtained. Besides, itis found that the prepared Cu2ZnSnS4 thin film has the electrocatalytic activity toward the redox reaction of I3?/I? and the dye-sensitized solar cell with the prepared Cu2ZnSnS4 thin film as the counter electrode achieves the efficiency of 1.09%.

Cu(In,Al)(S,Se)_2薄膜的三靶共溅射制备与性能表征

采用磁控三靶共溅射的方法在玻璃衬底上沉积出了Cu-In-Al预制膜,后经硫硒化工艺得到了Cu(In,Al)(S,Se)2(CIASSe)薄膜吸收层,并利用XRD、EDAX、紫外-可见分光光度计等对薄膜样品结构、成分和光电性能进行了表征。研究了溅射功率、硫硒化温度及时间等工艺参数对CIASSe薄膜的结构、成分及光电性能的影响。结果表明:在CIA30W,Al60W,Cu50W三靶共溅的组合功率下,在540℃热处理,20 min后所得薄膜为贫铜的黄铜矿结构,晶体的晶化较好,晶粒沿着(112)晶向择优生长,薄膜成分接近理想的化学计量比,表面致密均匀,且其光学带隙约为1.40 eV,是性能较为良好的太阳能吸收层薄膜。

Low-temperature phase transformation of CZTS thin films

The low temperature phase transformation in the Cu_2ZnSnS_4（CZTS） films was investigated by laser annealing and low temperature thermal annealing.The Raman measurements show that a-high-power laser annealing could cause a red shift of the Raman scattering peaks of the kesterite（KS） structure and promotes the formation of the partially disordered kesterite（PD-KS） structure in the CZTS films,and the low-temperature thermal annealing only shifts the Raman scattering peak of KS phase by several wavenumber to low frequency and the broads Raman peaks in the low frequency region.Moreover,the above two processes were reversible.The Raman analyses of the CZTS samples prepared under different process show that the PD-KS structure tends to be found at low temperatures and low sulfur vapor pressures.Our results reveal that the control of the phase structure in CZTS films is feasible by adjusting the preparation process of the films.

Cu_(2)Zn(Sn_(1-x)Ge_(x))(S,Se)_(4)太阳能电池的制备和表征

采用简单的溶胶-凝胶法制备了高质量的Cu_(2)Zn(Sn_(1-x)Ge_(x))(S,Se)_(4)(CZTGSSe)前驱体薄膜.在500℃下进行17 min的硒化,得到了高质量的CZTGSSe薄膜.利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、紫外-可见分光光度计(UV-Vis)等研究了CZTGSSe薄膜的物理化学性质.实验结果表明,利用在CZTSSe吸收层中掺杂Ge的方法可以得到较高的迁移率和光电转换效率(PCE).与Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)太阳能电池相比,观察到5%-CZTGSSe太阳能电池的开路电压(V_(oc))增加了104 mV,PCE也从3.14%增加到5.28%.因此,在CZTSSe层中掺杂Ge不仅是一种可以获得具有较高V_(oc)和PCE的CZTSSe基太阳能电池的方法,也是一种可以促进晶粒生长、提高薄膜质量的有效途径.

Al_(2)O_(3)扩散阻挡层对柔性CZTSSe薄膜及其太阳电池的性能影响

柔性Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)薄膜太阳电池因具有轻便、灵活、可弯折等优点,可广泛应用于柔性电子器件和便捷式可穿戴设备。但柔性CZTSSe薄膜中的应力问题严重限制了其效率的提升。采用磁控溅射法在柔性Ti衬底和Mo背电极层之间溅射Al_(2)O_(3)扩散阻挡层来减小柔性CZTSSe薄膜中的残余应力。系统研究了Al_(2)O_(3)扩散阻挡层厚度对CZTSSe薄膜物相结构、微观形貌、残余应力以及器件性能的影响。结果表明,Al_(2)O_(3)扩散阻挡层的引入可有效提高CZTSSe薄膜的结晶质量,减小残余应力,降低缺陷密度,从而抑制载流子的复合。当Al_(2)O_(3)扩散阻挡层厚度为40 nm时,CZTSSe薄膜表现出最佳的结构、形貌和光电特性,相比没有引入Al_(2)O_(3)扩散阻挡层,CZTSSe薄膜的残余应力由-3.99 GPa减小至-2.06 GPa,其太阳电池光电转换效率由2.61%提升至4.21%。

Preparation and Characterization of Cu_2ZnSn(S_xSe_(1-x))_4Thin Films by Synchronous Sulfo-Selenization of Single-Source Evaporated Metallic Precursors

Cu2ZnSn（S,Se）4（CZTSSe） thin film was prepared using a simple two-step approach based on the single-source evaporation and synchronous sulfo-selenization.Composition,microstructure,morphology,and properties of the asprepared CZTSSe thin films were investigated.XRD and Raman patterns confirmed the formation of single-phase CZTSSe solid solutions.SEM results showed that the CZTSSe thin film had a uniform morphology and large grains.EDS results revealed the composition of CZTSSe film was Cu：Zn：Sn：S：Se = 23.7：12.6：12.2：37.7：13.8（in at%）,which was in accordance with the stoichiometric Cu2ZnSn（S,Se）4.The optical band gap of CZTSSe thin film evaluated from its UV–Vis spectrum was 1.33 eV.The resistivity,carrier concentration,and mobility were 0.53 X cm,7.9 9 1018cm3,and 7.5 cm2/（Vs）,respectively.