Interface optimization and defects suppression via Na F introduction enable efficient flexible Sb_(2)Se_(3) thin-film solar cells

Sb_(2)Se_(3) with unique one-dimensional(1D) crystal structure exhibits exceptional deformation tolerance,demonstrating great application potential in flexible devices.However,the power conversion efficiency(PCE) of flexible Sb_(2)Se_(3) photovoltaic devices is temporarily limited by the complicated intrinsic defects and the undesirable contact interfaces.Herein,a high-quality Sb_(2)Se_(3) absorber layer with large crystal grains and benign [hkl] growth orientation can be first prepared on a Mo foil substrate.Then NaF intermediate layer is introduced between Mo and Sb_(2)Se_(3),which can further optimize the growth of Sb_(2)Se_(3)thin film.Moreover,positive Na ion diffusion enables it to dramatically lower barrier height at the back contact interface and passivate harmful defects at both bulk and heterojunction.As a result,the champion substrate structured Mo-foil/Mo/NaF/Sb_(2)Se_(3)/CdS/ITO/Ag flexible thin-film solar cell delivers an obviously higher efficiency of 8.03% and a record open-circuit voltage(V_(OC)) of 0.492 V.This flexible Sb_(2)Se_(3) device also exhibits excellent stability and flexibility to stand large bending radius and multiple bending times,as well as superior weak light photo-response with derived efficiency of 12.60%.This work presents an effective strategy to enhance the flexible Sb_(2)Se_(3) device performance and expand its potential photovoltaic applications.

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.

Performance improvement of CdS/Cu(In,Ga)Se_2 solar cells after rapid thermal annealing

In this paper, we investigated the effect of rapid thermal annealing （RTA） on solar cell performance. An opto-electric conversion efficiency of 11.75% （Voc = 0.64 V, Jsc = 25.88 mA/cm2, FF=72.08%） was obtained under AM 1.5G when the cell was annealed at 300℃ for 30 s. The annealed solar cell showed an average absolute efficiency 1.5% higher than that of the as-deposited one. For the microstructure analysis and the physical phase confirmation, X-ray diffraction （XRD）, Raman spectra, front surface reflection （FSR）, internal quantum efficiency （IQE）, and X-ray photoelectron spectroscopy （XPS） were respectively applied to distinguish the causes inducing the efficiency variation. All experimental results implied that the RTA eliminated recombination centers at the p-n junction, reduced the surface optical losses, enhanced the blue response of the CdS buffer layer, and improved the ohmic contact between Mo and Cu（In, Ga）Se2 （CIGS） layers. This leaded to the improved performance of CIGS solar cell.

Non-ionizing energy loss calculations for modeling electron-induced degradation of Cu(In,Ga)Se_2 thin-film solar cells

The lowest energies which make Cu,In,Ga,and Se atoms composing Cu（In,Ga）Se_2（CIGS） material displaced from their lattice sites are evaluated,respectively.The non-ionizing energy loss（NIEL） for electron in CIGS material is calculated analytically using the Mott differential cross section.The relation of the introduction rate（k） of the recombination centers to NIEL is modified,then the values of k at different electron energies are calculated.Degradation modeling of CIGS thin-film solar cells irradiated with various-energy electrons is performed according to the characterization of solar cells and the recombination centers.The validity of the modeling approach is verified by comparison with the experimental data.

单靶磁控溅射Cu(In,Ga)Se_(2)太阳电池的背接触界面设计

通过磁控溅射单一四元靶材磁控得到的黄铜矿Cu(In,Ga)Se_(2)(CIGS)太阳电池开发的主要瓶颈是严重的载流子复合,其开路电压非常低.CIGS与钼(Mo)之间不良的缺陷环境是吸收体和界面复合严重的主要原因之一.其中,在背界面处引入的CuGaSe_(2)(CGS)低温缓冲层可以有效地抑制吸收体与背电极在高温磁控过程中的不利界面反应,从而获得高质量的晶体.通过这种背界面工程,不仅可以很好地解决吸收体和界面质量不佳的问题,而且有利于在吸收层中形成梯度带隙结构,从而使深能级InGa缺陷转换为较低能级的VCu缺陷,最终CIGS太阳电池的转换效率达到15.04%.这项工作为直接溅射高效率CIGS太阳电池的产业化提供了一种新的方法.

Review on Alkali Element Doping in Cu（In,Ga）Se2 Thin Films and Solar Cells

This paper reviews the development history of alkali element doping on Cu（In,Ga）Se2 （CIGS） solar cells and summarizes important achievements that have been made in this field. The influences of incorporation strategies on CIG5 absorbers and device performances are also reviewed. By analyzing CIGS surface structure and electronic property variation induced by alkali fluoride （NaF and KF） post-deposition treatment （PDT）, we discuss and interpret the following issues： ① The delamination of CIGS thin films induced by Na incorporation facilitates CulnSe2 formation and inhibits Ga during low-temperature co-evaporation process- es. ② The mechanisms of carrier density increase due to defect passivation by Na at grain boundaries and the surface. ③ A thinner buffer layer improves the short-circuit current without open-circuit voltage loss, This is attributed not only to better buffer layer coverage in the early stage of the chemical bath deposition process, but also to higher donor defect （Cd^＋Cu） density, which is transferred from the acceptor defect （C^-cu） and strengthens the buried homojunction. ④ The KF-PDT-induced lower valence band maximum at the absorber surface reduces the recombination at the absorber/buffer interface, which improves the open-circuit voltage and the fill factor of solar cells.

Interpenetrating structure for efficient Sb_(2)Se_(3) nanorod array solar cells loaded with CuInSe_(2) QDs sensitizer

The strong anisotropic electrical properties of one-dimensional(1 D) nanostructure semiconductors,especially the anisotropic carrier transport, have a negative and significant influence on the performance of solar cells if the nanostructures have random orientation. Considering the advantages of nanorod solar cells in carrier transport, we have achieved growth of vertically aligned Sb_(2)Se_(3) nanorod array with highly(hk1) orientation on Cd S substrate, and constructed superstrate nanorod solar cells for the first time. The Sb_(2)Se_(3) nanorod array solar cells exhibit the more efficient and long-range carrier transport in vertical direction. Furthermore, in order to suppress interface recombination, a CuInSe_(2) quantum dots(QDs) sensitizer has been applied to fill the volume between the nanorods completely, thus forming an interpenetrating nanocomposite structure. The CuInSe_(2) QDs can harvest additional light by absorption of visible light and contribute photocurrent. Meantime, the QDs function as a hole transport material and thus reduce the dependence of lateral transport. Consequently, the interpenetrating nanocomposite CuInSe_(2) / Sb_(2)Se_(3) solar cells display a power conversion efficiency of 7.54% with significant enhancements in the short-circuit current density and open-circuit voltage over pure Sb_(2)Se_(3) nanorod cells. This is the highest efficiency for superstrate solar cells based on Sb_(2)Se_(3) nanorod arrays.

Enhanced efficiency of the Sb_(2)Se_(3)thin-film solar cell by the anode passivation using an organic small molecular of TCTA

Antimony selenide(Sb_(2)Se_(3))is an emerging solar cell material.Here,we demonstrate that an organic small molecule of 4,4',4''-tris(carbazol-9-yl)-triphenylamine(TCTA)can efficiently passivate the anode interface of the Sb_(2)Se_(3)solar cell.We fabricated the device by the vacuum thermal evaporation,and took ITO/TCTA(3.0 nm)/Sb_(2)Se_(3)(50 nm)/C60(5.0 nm)/Alq3(3.0 nm)/Al as the device architecture,where Alq3 is the tris(8-hydroxyquinolinato)aluminum.By introducing a TCTA layer,the open-circuit voltage is raised from 0.36 to 0.42 V,and the power conversion efficiency is significantly improved from 3.2%to 4.3%.The TCTA layer not only inhibits the chemical reaction between the ITO and Sb_(2)Se_(3)during the annealing process but it also blocks the electron diffusion from Sb_(2)Se_(3)to ITO anode.The enhanced performance is mainly attributed to the suppression of the charge recombination at the anode interface.

基于机器学习和器件模拟对Cu(In,Ga)Se_(2)电池中Ga含量梯度的优化分析

Cu(In,Ga)Se_(2)(CIGS)太阳能电池是一种高效薄膜太阳能电池,Ga含量(Ga/(Ga+In),GGI)梯度调控是在不损失短路电流情况下,获得高开路电压的一种有效方法.本文基于对薄膜电池效率极限的对比分析,首先评估了CIGS电池性能提升的优化空间和策略.进而,通过机器学习与电池模拟分析相结合,研究了不同类别的“V”型GGI梯度对电池性能的影响,优化了“V”型双梯度的分布,获得了高于26%的模拟效率,并探究了其内部载流子作用机理.本文的研究提供了获得高效率CIGS电池“V”型GGI梯度的优化方案,为实验优化提供了指导.

Boosting Cu(In,Ga)Se_(2)Thin Film Growth in Low-Temperature Rapid-Deposition Processes:An Improved Design for the Single-Heating Knudsen Effusion Cell

The Knudsen effusion cell is often used to grow high-quality Cu(In,Ga)Se_(2)(CIGS)thin film in coevaporation processes.However,the traditional single-heating Knudsen effusion cell cannot deliver complete metal selenides during the whole deposition process,particularly for a low-temperature deposition process,which is probably due to the condensation and droplet ejection at the nozzle of the crucible.In this study,thermodynamics analysis is conducted to decipher the reason for this phenomenon.Furthermore,a new single-heating Knudsen effusion is proposed to solve this difficult problem,which leads to an improvement in the quality of CIGS film and a relative increase in conversion efficiency of 29%at a growth rate of about 230 nmmin1,compared with the traditional efficiency in a lowtemperature rapid-deposition process.

Double interface modification promotes efficient Sb2Se3 solar cell by tailoring band alignment and light harvest

The band alignment at the front interfaces is crucial for the performance of Sb_(2)Se_(3) solar cell with superstrate configuration.Herein,a Sn O_(2)/Ti O_(2) thin film,demonstrated beneficial for carrier transport in Sb_(2)Se_(3) device by the first-principle calculation and experiment,is proposed to reduce the parasitic absorption caused by CdS and optimize the band alignment of Sb_(2)Se_(3) solar cell.Thanks to the desirable transmittance of SnO_(2)/TiO_(2) layer,the Sb_(2)Se_(3) solar cell with SnO_(2)/TiO_(2)/(CdS-38 nm) electron transport layer performances better than (CdS-70 nm)/Sb_(2)Se_(3) solar cell.The optimized band alignment,the reduced interface defects and the decreased current leakage of Sb_(2)Se_(3) solar cell enable the short-circuit current density,fill factor,open-circuit voltage and efficiency of the Sb_(2)Se_(3) solar cell increase by 26.7%,112%,33.1%and 250%respectively when comparing with TiO_(2)/Sb_(2)Se_(3) solar cell without modification.Finally,an easily prepared Sn O_(2)/Ti O_(2)/CdS ETL is successfully applied on Sb_(2)Se_(3) solar cell by the first time and contributes to the best efficiency of 7.0%in this work,which is remarkable for Sb_(2)Se_(3) solar cells free of hole transporting materials and toxic CdCl_(2) treatment.This work is expected to provide a valuable reference for future ETL design and band alignment for Sb_(2)Se_(3) solar cell and other optoelectronic devices.

Back contact interfacial modification mechanism in highly-efficient antimony selenide thin-film solar cells

Antimony selenide(Sb_(2)Se_(3))is a potential photovoltaic(PV)material for next-generation solar cells and has achieved great development in the last several years.The properties of Sb_(2)Se_(3)absorber and back contact influence the PV performances of Sb_(2)Se_(3)solar cells.Hence,optimization of back contact characteristics and absorber orientation are crucial steps in raising the power conversion efficiency(PCE)of Sb_(2)Se_(3)solar cells.In this work,MoO2was introduced as an intermediate layer(IL)in Sb_(2)Se_(3)solar cells,and comparative investigations were conducted.The growth of(211)-oriented Sb_(2)Se_(3)with large grains was facilitated by introducing the MoO2IL with suitable thickness.The MoO2IL substantially lowered the back contact barrier and prevented the formation of voids at the back contact,which reduced the thickness of the MoSe2interface layer,inhibited carrier recombination,and minimized bulk and interfacial defects in devices.Subsequently,significant optimization enhanced the open-circuit voltage(VOC)of solar cells from 0.481 V to 0.487 V,short-circuit current density(JSC)from 23.81 m A/cm^(2)to 29.29 m A/cm^(2),and fill factor from 50.28%to 57.10%,which boosted the PCE from 5.75%to 8.14%.

Preparation of High Ga Content Cu(In,Ga)Se₂Thin Films by Sequential Evaporation Process Added In₂S₃

High Ga content Cu(In,Ga)Se2 thin films incorporated sulfur were prepared by sequential evaporation from CuGaSe2 and CuInSe2 ternary compounds and subsequently Ga2Se3, In2Se3 and In2S3 binary compounds. The In2S3/(Ga2Se3+ In2Se3) ratio was varied from 0 to 0.13, and the properties of the thin films were investigated. XRD studies demonstrated that the prepared thin films had a chalcopyrite Cu(In,Ga)Se2 structure. The S/(Se+S) mole ratio in the thin films was within the range from 0 to 0.04. The band gaps of Cu(In,Ga)Se2 thin films increased from 1.30 eV to 1.59 eV with increasing the ?In2S3 /(Ga2Se3+ In2Se3) ratio.

Review on incorporation of alkali elements and their effects in Cu(In,Ga)Se_(2)solar cells

Cu(In,Ga)Se_(2)(CIGS)is a promising candidate to replace crystalline silicon solar cells and dominate the photovoltaic market in the future.Alkali elements such as sodium(Na),potassium(K),rubidium(Rb),and Cesium(Cs)are commonly accepted as indispensable parts to boost cell efficiencies of CIGS thin-film solar cells.Therefore,a comprehensive understanding of alkali effects on the electronic and chemical properties of the CIGS layer as well as the underlying mechanisms is of paramount importance for achieving high-performance solar cells.This paper reviews the development process and incorporation pathways of alkalis and then overviews the roles of different alkali elements and their effects on CIGS cells in detail.Furthermore,the unsolved problems and future development prospects are also proposed.Overall,the understanding and development of widely adopted alkali-fluoride post-deposition treatments(PDTs)are still underway,and together with newly updated research,it will likely enable the CIGS technology to make the conversion efficiency closer to its theoretical limit.

Model for increased efficiency of CIGS solar cells by a stepped distribution of carrier density and Ga in the absorber layer

In this paper, several structures for multilayer Cu(In1-xGax) Se2 (CIGS) thin film solar cells are proposed to achieve high conversion efficiency. All of the modeling and simulations were based on the actual data of experimentally produced CIGS cells reported in the literature. In standard CIGS cells with a single absorber layer, the effects of acceptor density and Ga content on device performance were studied, and then optimized for maximum conversion efficiency. The same procedure was performed for cells with two and three sectioned CIGS absorber layers in which Cu and/or Ga contents were varied within each consecutive section. This produces an internal additional electric field within the absorber layer, which resulted in an increase in carrier collection for longer wavelength photons, and hence, improvement in the conversion efficiency of the cell. An increase of approximately 3% in efficiency is predicted for cells with two layer absorbers. For multilayer cells in which Cu and Ga distribution were stepped simultaneously, the improvement could be approximately 3.5%. This improvement is due to; enhanced carrier collection for longer-wavelength photons, and reduced recombination at the heterojunction and back regions of the cell. These results are confirmed by the physics of the cells.

Ion doping simultaneously increased the carrier density and modified the conduction type of Sb_(2)Se_(3) thin films towards quasi-homojunction solar cell

Antimony selenide(Sb_(2)Se_(3))has drawn tremendous research attentions in recent years as an environment-friendly and cost-efficient photovoltaic material.However,the intrinsic low carrier density and electrical conductivity limited its scope of applications.In this work,an effective ion doping strategy was implemented to improve the electrical and photoelectrical performances of Sb_(2)Se_(3) thin films.The Sn-doped and I-doped Sb_(2)Se_(3) thin films with controllable chemical composition can be prepared by magnetron sputtering combined with post-selenization treatment based on homemade plasma sintered targets.As a result,the Sn-doped Sb_(2)Se_(3) thin film exhibited a great increase in carrier density by several orders of magnitude,by contrast,a less increase with one order of magnitude was achieved for the Idoped Sb_(2)Se_(3) thin film.Additionally,such cation or anion doping could simultaneously modify the conduction type of Sb_(2)Se_(3),enabling the first fabrication of a substrate structured Sb_(2)Se_(3)-based quasihomojunction thin film solar cell with configuration of Mo/Sb_(2)Se_(3)-Sn/Sb_(2)Se_(3)-I/ITO/Ag.The obtained power conversion efficiency exceeding 2%undoubtedly demonstrated its attractive photovoltaic application potential and further investigation necessity.

薄膜太阳电池的研究进展及应用前景

阐述了非晶硅薄膜电池、多晶硅薄膜电池、锑化镉薄膜电池、铜铟镓硒薄膜太阳电池和染料敏化TiO2太阳电池的研究现状,简要介绍了我国薄膜太阳电池研究的进展,指出了太阳电池在我国的应用前景。

太阳电池新材料新方法

该文叙述了发展低成本、高效率太阳电池光伏有源材料CuIn1 xGaxSe2 (CIGS)和新式薄膜电淀积技术的优点。详细报告了该研究项目采用的新式CIGS薄膜电淀积的整个实验制作过程 ,给出了在香港政府创新科技基金资助下的第一阶段所取得的成果。实验结果已证明 :采用这种简单而新颖的电淀积方法能制得光伏用的多晶半导体CIGS薄膜材料。通过测试确定了这种材料具有四方晶体结构、特征峰为 (112 ) ,(2 0 4,2 2 0 )的多晶CIGS材料。已测得连续分布的薄膜层厚约 1 6 μm ,晶粒的平均大小约 2 μm长 ,具有太阳电池所需的材料质量。实验还证明 :此法可重覆生产出厚度和质量相近的CIGS薄膜。该文也做了有关技术的讨论和分析。这种新式的材料和薄膜技术对生产商品化低成本、高效率薄膜太阳电池无疑是非常有希望的。

铜锌锡硫硒太阳能电池Mo/CZTSSe界面调控研究进展

Cu_(2)ZnSn(S_(x),Se_(1-x))_(4)太阳能电池制备过程中Mo基底硒(硫)化反应产生较厚的Mo(S_(x),Se_(1-x))_(2),以及SnS(e)与ZnS(e)的生成与挥发在Mo/CZTSSe界面处产生的孔洞,是限制器件性能提升的重要原因。针对这些问题,总结了Mo(S_(x),Se_(1-x))_(2)和孔洞的生成原因及其对器件性能的影响。此外,还综述了金属氮化物、金属氧化物、金属硫化物等材料作为Mo/CZTSSe界面中间层在抑制Mo(S_(x),Se_(1-x))_(2)和孔洞产生中的作用。最后,展望了该领域未来的研究方向。

VTD法制备不同基底倾角的硒化锑薄膜及太阳电池

硒化锑(Sb_(2)Se_(3))具有较高丰度及良好的光电特性,是当前热门太阳电池材料之一。目前,在Sb_(2)Se_(3)的多种制备方法中,气相转移沉积法(VTD)因工艺简单且可大面积制备而备受关注。采用VTD法制备Sb_(2)Se_(3)薄膜的影响因素有多种,如腔体气压、反应温度、蒸发源与衬底的位置以及生长角度等。本文利用VTD法以不同的生长角度(30°、45°、60°、90°)制备了Sb_(2)Se_(3)薄膜,对其进行XRD、Raman、SEM、近红外-紫外反射表征。结果表明不同生长角度对薄膜的结构以及光学特性具有明显的影响。晶粒尺寸随着生长角度的增加而先增大后减小,同时薄膜的形貌由棒状生长转变为片状生长,在基底倾角为90°时,薄膜变得最为致密。近红外-紫外反射光谱表明倾角60°的样品在波长小于1100 nm的范围具有最低的反射率,在该角度下制备的FTO/CdS/Sb_(2)Se_(3)/C器件获得了2.38%的转换效率。