衬底对Cu(In,Ga)Se2薄膜织构的影响

分别在苏打石灰玻璃、Mo箔、无择优取向的Mo薄膜以及(110)择优取向的Mo薄膜四种不同衬底上，采用共蒸发工艺沉积约2 μm厚的Cu(In,Ga)Se₂薄膜，用X射线衍射仪测量薄膜的织构，研究衬底对Cu(In,Ga)Se₂薄膜织构的影响.在以上四种衬底上沉积的Cu(In,Ga)Se₂薄膜的(112)衍射峰强度依次逐渐减弱，(220/204)衍射峰从无到有且强度逐渐增强.在苏打石灰玻璃和Mo箔衬底上的Cu(In,Ga)Se_{2关键词： 择优取向 Cu(In 2}薄膜')" href="#">Ga)Se₂薄膜 太阳电池     

Local current–voltage behaviors of preferentially and randomly textured Cu(In,Ga)Se2 thin films investigated by conductive atomic force microscopy

Electrical transport properties on polycrystalline Cu(In,Ga)Se₂ (CIGS) (Ga/(In+Ga) ≈35%) thin films were examined by conductive atomic force microscopy. The CIGS thin films with a (112) preferential or random texture were deposited on Mo-coated glass substrates. Triangular pyramidal grain growths were observed in the CIGS thin films preferentially textured to the (112) planes. Current maps of the CIGS surface were acquired with a zero or non-zero external voltage bias. The contrast of the images on the grain boundaries and intragrains displayed the conduction path in the materials. Local current–voltage measurements were performed to evaluate the charge conduction properties of the CIGS thin films.     

Characterization of Cu(In,Ga)Se2 thin films prepared by evaporationfrom ternary compounds

Thin films of Cu(In,Ga)Se₂ were fabricated by evaporation from ternary CuGaSe₂ and CuInSe₂ compounds for photovoltaic device applications and their properties were investigated. From XRF analysis, the Cu:(In+Ga):Se atomic ratio in all thin films was approximately 1:1:2. The Ga/(In+Ga) atomic ratio in the thin films changed linearly from 0 to 1.0 with increasing the [CGS]/([CGS]+[CIS]) mole ratio in the evaporating materials. However, for thin films prepared at the [CGS]/([CGS]+[CIS]) mole ratio above 0.4, the composition by EPMA analysis was not consistent with that by XRF analysis. The result of EPMA analysis showed that the surface of a thin film was Cu-rich. XRD studies demonstrated that the thin films prepared at the [CGS]/([CGS]+[CIS]) mole ratio under 0.2 had a chalcopyrite Cu(In,Ga)Se₂ structure and the preferred orientation to the 112 plane. On the other hand, XRD patterns of the thin films produced at the [CGS]/([CGS]+[CIS]) mole ratio above 0.6 showed the diffraction lines from a chalcopyrite Cu(In,Ga)Se₂ and a foreign phase. The separation of a peak was observed near 2θ=27°, indicative the graded Ga concentration in Cu(In,Ga)Se₂ thin film.     

低温生长Cu(InGa)Se2薄膜吸收层的掺钠工艺研究

在柔性聚酰亚胺衬底上低温制备Cu(In,Ga)Se₂薄膜太阳能电池, Na的掺入会改善电池特性, 但不同的掺Na工艺对Cu(In,Ga)Se₂薄膜和器件特性的改善机理不同. 本实验通过对比前掺NaF和后掺NaF工艺发现, 在前掺Na工艺下, 由于Na始终存在于Cu(In,Ga)Se₂薄膜生长过程中, Na存在于多晶 Cu(In,Ga)Se₂ 薄膜晶界处, 起到了扩散势垒的作用, 导致晶粒细碎、加剧两相分离, 同时减小了施主缺陷的形成概率; 而在后掺Na工艺下, 掺入的Na对薄膜的结构及生长不产生影响, 仅仅起到了钝化施主缺陷、改善薄膜缺陷态的作用. 同时, 研究表明, 后掺Na工艺中, NaF必须依靠外界能量辅助才能扩散进Cu(In,Ga)Se₂内部, 实验结果证实, 只有衬底温度达到350 ℃以上时, 掺入的NaF才能较好地改善薄膜特性. 最终经掺Na工艺的优化, 得到低温工艺制备的柔性聚酰亚胺衬底器件效率达10.4%.     

Investigation of local electronic transport and surface potential distribution of Cu(In,Ga)Se2 thin-films

Local current mapping and surface potential distributions on polycrystalline Cu(In,Ga)Se₂ (CIGS) films are investigated by conductive atomic force microscopy and Kelvin probe force microscopy. The two kinds of samples fabricated by co-evaporation had extremely different conversion efficiencies of 10% and 0.2% for stoichiometric and Cu- and Se-deficient compositions, respectively. We examined the microscopic reasons for the differences in the local electrical properties. Current mapping and current–voltage behaviors were measured at intragrain regions (IGs) and grain boundaries (GBs). Electronic transport between a Pt scanning probe and the CIGS layer is explained by the Schottky conduction mechanism. The surface potential distribution shows an intriguing relation with topological variation, inferring that a local built-in potential is possibly formed on positively charged GBs. The surface potential is about 100 mV, which shows energy band bending near GBs in the films. Exciton separation near GBs is explained by the bending of the conduction and valence bands, which is sensitive to compositional and structural inhomogeneities.     

A non-selenization technology by co-sputtering deposition for solar cell applications

This work presents a novel method to form polycrystalline Cu(In(1-x)Ga(x))Se(2) (CIGS) thin film by co-sputtering of In─Se and Cu─Ga alloy targets without an additional selenization process. An attempt was also made to thoroughly elucidate the surface morphology, crystalline phases, physical properties, and chemical properties of the CIGS films by using material analysis methods. Experimental results indicate that CIGS thin films featured densely packed grains and chalcopyrite phase peaks of (112), (220), (204), (312), and (116). Raman spectroscopy analysis revealed chalcopyrite CIGS phase with Raman shift at 175 cm(-1), while no signal at 258 cm(-1) indicated the exclusion of Cu(2-x)Se phase. Hall effect measurements confirmed the polycrystalline Cu(In,Ga)Se₂ thin film to be of p type semiconductor with a film resistivity and mobility of 2.19×10(2) Ω cm and 88 cm(2)/V s, respectively.     

The effect of Na on the electronic properties of Cu(In,Ga)Se2 thin films: A local‐probe study

We investigated the effect of Na incorporation on the electronic properties of polycrystalline CuIn_0.7Ga_0.3Se₂ thin films using scanning tunneling microscopy and spectroscopy. The tunneling spectra indicate a reduced in‐gap density of states at grain boundaries and reveal a downward band‐bending in Na‐rich grain boundaries with respect to the adjacent grains, in agreement with our conductive atomic force microscopy data. It thus appears that Na passivates deep‐level defects at grain boundaries and induces a downward band‐bending there. Moreover, we provide evidence that Na passivates mainly Cu vacancy related defects. We suggest that the grain‐boundary passivation, which reduces the recombination rate of photogenerated carriers, is at least of major importance in the well known Na‐induced improvement in the efficiency of the corresponding solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Direct insight into grain boundary reconstruction in polycrystalline Cu(In,Ga)SE2 with atomic resolution

This work presents results from high-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy on twin boundaries (TBs) and nontwin grain boundaries (GBs) in Cu(In,Ga)Se(2) thin films. It is shown that the atomic reconstruction is different for different symmetries of the grain boundaries. We are able to confirm the model proposed by Persson and Zunger [Phys. Rev. Lett. 91, 266401 (2003)] for Se-Se-terminated Σ3 {112} TBs, showing Cu depletion and In enrichment in the two atomic planes closest to the TB. On the contrary, Cu depletion without In enrichment is detected for a cation-Se-terminated TB. At nontwin GBs, always a strong anticorrelation of Cu and In signals is detected suggesting that the formation of In(Cu) or Cu(In) antisites within a very confined region of smaller than 1 nm is an essential element in the reconstruction of these GBs.     

Preparation of Cu（In,Ga）Se2 Thin Film Solar Cells by Selenization of Metallic Precursors in an Ar Atmosphere

Cu（In, Ga）Se2 thin films are deposited on Mo-coated glass substrates by Se vapour selenization of sputtered metallic precursors in the atmosphere of Ar gas flow under a pressure of about 10 Pa. The in situ heat treatment of as-grown precursor leads to the formation of a better alloy. During selenization, the growth of CuInSe2 phase preferably proceeds through Se-poor phases as CuSe and InSe at relatively low substrate temperature of 250℃, due to the absence of In2Se3 at intermediate stage at low reactor pressure. Subsequently, the Cu（In,Ga）Se2 phase is produced by the reactive diffusion of CuInSe2 with a Se-poor GaSe phase at high temperature of up to 560℃. The final film exhibits smooth surface and large grain size. The absorber is used to fabricate a glass/Mo/Cu（In, Ga）Se2/CdS/ZnO cell with the total-area efficiency of about 7%. The low open-circuit voltage value of the cell fabricated should result from the nonuniform distribution of In and Ga in the absorber, due to the diffusion-controlled reaction during the phase formation. The films, as well as devices, are characterized.     

Cu(In,Sn)Se2 thin films for absorption of energy from infrared radiation

In this study, we sought to lower the bandgap of thin film solar cells by replacing the Ga used in the absorber layer of Cu(In,Ga)Se₂ with Sn (bandgap of 0.07?eV) to form Cu(In,Sn)Se₂. The proposed scheme was shown to reduce the bandgap of the absorber layer from 1.0?eV to 0.88?eV. Sn films of various thicknesses were deposited using precursors of Sn–In–Cu metal in order to study the effects of Sn/(In?+?Sn) ratio (SIR) on the structure of the material and photoelectrical characteristics of the Cu(In,Sn)Se₂ absorber layer. Experiment results revealed that a higher SIR following selenization increased the grain size and surface roughness of the absorber layer. It increased the quantity of secondary phases of SnSe₂ and Cu₂SnSe₃ and improved the distribution of Cu and In in the absorber layer. A higher SIR was also shown to increase electron mobility while decreasing carrier concentration and conductivity. When SIR≧0.25, the replacement of In³⁺ with Sn⁴⁺in the Cu⁺ vacancies decreased the electron strength of In. We speculate that an increase in SIR caused a relative increase in the quantity of Sn²⁺ compared to Sn⁴⁺, thereby increasing the electron strength of Sn and switching the absorber layer from a p-type to an n-type semiconductor.     

Structural and optical properties of CdS/Cu(In,Ga)Se<Subscript>2</Subscript> heterostructures irradiated by high-energy electrons*

Thin films of Cu(In, Ga)Se₂ (CIGS) with a Ga/(Ga + In) ratio of ~0.27 corresponding to the standard elemental composition for solar-energy transducers were grown on Mo-coated glass substrates by the Cu, In, Ga, and Se co-evaporation technique from different sources. Transmission (T), photoluminescence (PL), and photoluminescence excitation (PLE) spectra at 4.2 K were used to analyze electronic properties in the asgrown and electron-irradiated CIGS films. The band-gap energy (E_g) of the CIGS films measured using both transmission and PLE methods was found to be about 1.28 eV at 4.2 K. Two deep bands in the PL spectra of the irradiated CIGS films, P₁ at ~0.91 eV and P₂ at ~0.77 eV, have been detected. These bands are tentatively associated with copper atoms substituting indium (Cu_In) and indium vacancies V_In, respectively, as the simplest radiation-induced defects.     

低温超薄高效Cu(In,Ga)Se2太阳电池的实现

衬底温度保持恒定, 在Se气氛下按照一定的元素配比顺序蒸发Ga, In, Cu制备厚度约为0.7 μrm的Cu(In_0.7Ga_0.3)Se₂ (CIGS)薄膜. 利用X射线衍射仪分析薄膜的晶体结构及物相组成, 扫描电子显微镜表征薄膜形貌及结晶质量, 二次离子质谱仪测试薄膜内部元素分布, 拉曼散射谱 分析薄膜表面构成, 带积分球附件的分光光度计测量薄膜光学性能. 研究发现在Ga-In-Se预制层内, In主要通过晶界扩散引起Ga/(Ga+In)分布均匀化. 衬底温度高于450 ℃时, 薄膜呈现单一的Cu(In_0.7Ga_0.3)Se₂相; 低于400℃, 薄膜存在严重的Ga的两相分离现象, 且高含Ga相主要存在于薄膜的上下表面; 低于300 ℃, 薄膜结晶质量进一步恶化. 薄膜表层的高含Ga相Cu(In_0.5Ga_0.5)Se₂以小晶粒形式均匀分布于薄膜表面, 增加了薄膜的粗糙度, 在电池内形成陷光结构, 提高了超薄电池对光的吸收. 加上带隙值较小的低含Ga相的存在, 使电池短路电流密度得到较大改善. 衬底温度在550 ℃–350 ℃变化时, 短路电流密度J_SC是影响超薄电池转换效率的主要因素; 而衬底温度T_sub低于300 ℃时, 开路电压V_OC和填充因子FF降低已成为电池性能减退的主要原因. T_sub为350 ℃时制备的0.7 μm左右的超薄CIGS电池转换效率达到了10.3%. 关键词： 2薄膜')" href="#">Cu(In,Ga)Se₂薄膜 衬底温度 超薄 太阳电池     

Deposition and characterization of Cu(In,Ga)Se2 thin films from the ink of sonochemically prepared CIGSe nanoparticles

CuIn_1-xGa_xSe₂ (CIGSe) nanoparticles were synthesized via a sonochemical method at different Ga content (x?=?0.15, 0.30 and 0.45) and dispersed in a low toxic isobutanol to form the nanoparticle-ink. Thin films of CIGSe were grown by a facile, non-vacuum and inexpensive “nanoparticle-ink based air-spray coating” method. Effects of Ga-content and annealing time on the physical properties of CIGSe thin films were investigated. The elemental composition, crystalline structure, surface morphology and optical properties of the films were explored by various characterization methods. XRD studies of as-synthesized films showed a tetragonal structure with (112) orientation. After annealing, the CIGSe films showed an improvement in the intensity ratio of I(220)/I(112) for the annealing time of 60?min. The morphological studies of annealed CIGSe films showed plank-like larger grains of size ～1–2?µm. The films deposited at different gallium content, x?=?0.15, 0.30 and 0.45 showed PL peak maxima at 954, 1049 and 1168?nm, respectively. The present method is capable of producing CIGSe absorbers by a greener route in large scales at lower cost.     

Microscopic evidence for the modification of the electronic structure at grain boundaries of Cu(In(1-x),Ga(x))Se2 films

We investigated the electronic properties around grain boundaries of polycrystalline Cu(In(1-x),Ga(x)Se(2)) films as a function of Ga content, using scanning tunneling spectroscopy. Spectra acquired on samples with low Ga content (x=0 and 0.33) reveal downward band bending with respect to adjacent p-type grains, suggesting type inversion at the surface of grain boundaries. Such a behavior was not observed for samples with high Ga contents. These results are consistent with our atomic force microscopy data and may shed light on the origin of the x-dependent efficiency for polycrystalline Cu(In(1-x),Ga(x)Se(2))-based solar cells.     

Cu（In,Ga）Se2 Thin Films on Flexible Polyimide Sheet： Structural and Electrical Properties versus Composition

The structural and electrical properties of Cu（In,Ga）Se2 （CIGS） films grown on polyimide （PI） sheet using the three-stage co-evaporation process are investigated by x-ray diffraction spectra （XRD）, scanning electron microscopy （SEM）, Raman spectra, and Hall effect measurements, respectively. The results show that the properties of CIGS films on PI sheet are strongly dependent on the compositional ratio of Cu/（In＋Oa） （Cu/Ⅲ）. In contrast to the non-stoichiometric CIGS films, stoichiometric CIGS films show better structural and electrical properties, such as a relatively larger grain size, lower resistivity and higher carrier concentration. The flexible CIGS solar cells on PI sheet with the conversion efficiencies of 9.7% and 6.6% are demonstrated for the CIGS absorber layer with Cu/Ⅲ of 0.96 and 0.76, respectively （active area, 0.20cm^2）. The cell efficiency for Cu-poor CIGS films is limited by a relatively lower open circuit voltage and fill factor.     

硒化前后电沉积贫铜和富铜的Cu(In1-xGax)Se2薄膜成分及结构的比较

采用电沉积法获得了接近化学计量比的贫铜和富铜的Cu（In_1-xGa_x）Se₂（CIGS）预置层,研究比较了两种预置层及其硒化处理后的成分和结构特性.得到了明确的实验证据证明,硒化后富铜薄膜中的Cu_xSe相会聚集凝结成结晶颗粒分散在表面.研究表明：在固态源硒化处理后,薄膜成分基本不变;当预置层中原子比Cu/（In+Ga）<11时,硒化后薄膜表面存在大量的裂纹;而当Cu/（In+Ga） >12时,可以消除裂纹的产生,形成等轴状小晶粒;富铜预置层硒化时蒸发沉积少量In,Ga和Se后,电池效率已达到68%;而贫铜预置层硒化后直接制备的电池效率大于2%,值得进一步深入研究. 关键词： 1-xGa_x）Se₂薄膜')" href="#">Cu（In_1-xGa_x）Se₂薄膜 电沉积 硒化处理 贫铜或富铜薄膜     

Correlation of structure parameters of absorber layer with efficiency of Cu(In,Ga)Se<Subscript>2</Subscript> solar cell

Polycrystalline Cu(In, Ga)Se₂ with Ga-content x=Ga/(In+Ga) ranging from 0.0 (CuInSe₂) to 1.0 (CuGaSe₂) in heterojunction thin film solar cells were grown by multi-source evaporation. Solar cells with a highest efficiency of η=15.3% need a composition of x≈0.2. At this composition, the c/a ratio of the lattice constants for the tetragonal lattice equals c/a=2, indicating ideal tetragonality. These results suggest that low electronic defect densities occur at x≈0.2, due to the smallest possible crystallographic distortion of the tetragonal lattice at this composition. Cells with high efficiencies require grain sizes above 145 nm and a high preferred orientation (P₂₀₄/P₂₂₀ pole density ratio) for the grains.     

Spectromicroscopic investigation of (NH4)2S treated polycrystalline Cu(In1−xGax)Se2

Device-grade polycrystalline thin-film Cu(In_1−xGa_x)Se₂ was treated with (NH₄)₂S at 60°C to determine the resulting microscopic surface composition/morphology. Scanning electron microscopy was used to evaluate the resultant macroscopic surface morphology. Modification of the surface and grain boundary chemistry of the Cu(In_1−xGa_x)Se₂ polycrystalline films was investigated with scanning photoemission spectromicroscopy. The submicrometer lateral resolution of this technique allows us to directly characterize not only the surface chemistry of the treated films on the submicron scale, but also to probe the grain boundary chemistry. Chemical maps depicting the distribution of chemical species on the surface and at grain boundaries were obtained by monitoring the S 2p, Se 3d, In 4d/Ga 3d and Cu 3d (valence band) photoelectrons while scanning the sample. Background maps were also acquired of each of the peak energies to separate chemical contrast from topographic contrast. Results show that S has been incorporated at the surface, possibly creating a wider bandgap Cu(In_1−xGa_x)(Se_1−yS_y)₂ surface layer, and along the grain boundaries. The purpose of this investigation is to find an environmentally safe replacement for the toxic CdS overlayer commonly used for heterojunction devices without sacrificing overall device performance and reliability.     

A new simple route to grow Cu(In,Ga)Se2 thin films with large grains in the co-evaporation process

In the conventional three-stage co-evaporation process to grow Cu(In,Ga)Se₂ (CIGS) film, a large grain is achieved by the co-evaporation of Cu and Se on (In,Ga)₂Se₃ layer at 550 °C in the second stage and then a p-type is achieved by the co-evaporation of In, Ga, and Se in the third-stage. We reported a new process where a CIGS film with a large gain and p-type is achieved by evaporation of Cu only in the second stage at 400 °C and by the Se annealing in the third stage. In the new process, thermal budget was lowered and the third-stage co-evaporation process was eliminated. It was found that the CIGS gain size increased when the Cu/(In + Ga) ratio was above 0.7 and an addition thin CIGS layer appeared on the CIGS surface. The reaction path with Cu was described in the Cu-In-Se ternary phase diagram. The cell conversion efficiency increased from 9.6 to 15.4% as the Se annealing temperature increased from 400 to 550 °C in the third stage, mainly due to the increase of open-circuit voltage and fill factor. Our process demonstrated a new route to grow a CIGS film with a less thermal budget and simpler process in the co-evaporation process.     

Structural and optical properties of thin films of Cu(In,Ga)Se<Subscript>2</Subscript> semiconductor compounds

The chemical composition of Cu(In,Ga)Se₂ (CIGS) semiconductor compounds is analyzed by local x-ray spectral microanalysis and scanning Auger electron spectroscopy. X-ray diffraction analysis reveals a difference in the predominant orientation of CIGS films depending on the technological conditions under which they are grown. The chemical composition is found to have a strong effect on the shift in the self-absorption edge of CIGS compounds. It is shown that a change in the relative proportion of Ga and In in CIGS semiconducting compounds leads to a change in the band gap E_g for this material in the 1.05–1.72 eV spectral range at 4.2 K.