共蒸发三步法制备CIGS薄膜的性质

采用PID温度控制器控制共蒸发设备中蒸发源及衬底加热的温度,以三步法工艺制备CIGS(Cu(In,Ga)Se2)薄膜,通过恒功率加热衬底测试温度的变化,可实现在线组分监测,得到CIGS薄膜的组成重现性很好.CIGS薄膜的表面光洁,粗糙度多数小于10nm.但是组成相同的CIGS薄膜,其结晶择优取向可能不同,主要有(112)和(220)/(204)两种;其结晶形貌也有很大的不同,晶粒粗大且成柱状的薄膜电池效率高,虽然从Cu/(In+Ga)＜1的组成可以认为CIGS薄膜为贫Cu结构,但Hall测试多数CIGS薄膜呈p型,少数呈n型.     

聚酰亚胺衬底CIGS薄膜附着性的改善

为改善聚酰亚胺(PI)衬底Cu(In,Ga)Se2(CIGS)薄膜的附着性,提出在NaF沉积前预先在Mo层上蒸发沉积100nm厚的In-Ga-Se(IGS)薄膜的新掺Na工艺。结果表明:这种IGS-NaF-CIGS式新工艺可显著改善CIGS薄膜的附着,而且CIGS薄膜材料和器件特性没有显著退化;新工艺促进了NaInSe2的生成,减少了In-Se二元相的残余,但也造成薄膜电阻率的升高和电池填充因子的下降,进而导致制备的PI衬底CIGS电池的转换效率由9.8%降至9.0%。综合考虑附着性的改善和器件效率的轻微下降,新工艺利大于弊,有很好的应用前景。     

共蒸发三步法制备CIGS薄膜的性质

采用PID温度控制器控制共蒸发设备中蒸发源及衬底加热的温度,以三步法工艺制备CIGS(Cu(In,Ga)Se2)薄膜,通过恒功率加热衬底测试温度的变化,可实现在线组分监测,得到CIGS薄膜的组成重现性很好.CIGS薄膜的表面光洁,粗糙度多数小于10nm.但是组成相同的CIGS薄膜,其结晶择优取向可能不同,主要有(112)和(220)/(204)两种;其结晶形貌也有很大的不同,晶粒粗大且成柱状的薄膜电池效率高,虽然从Cu/(In Ga)＜1的组成可以认为CIGS薄膜为贫Cu结构,但Hall测试多数CIGS薄膜呈p型,少数呈n型.     

CIGS薄膜(InGa)2Se3-富Cu-富In(Ga)的演变

采用三步共蒸发工艺顺序沉积铜铟镓硒(CuInGaSe2,CIGS)薄膜.薄膜的厚度、组份、晶相结构分别由台阶仪、X射线荧光光谱仪(XRF)和X射线衍射仪(XRD)来表征.在(In,Ga)2Se3预制层-富Cu相的演变过程中,依次发生以下相变:Cu(In,Ga)5Se8、Cu(In,Ga)3Se5、Cu2(In,Ga)4Se7(或Cu(In,Ga)2Se3.5)、Cu(In,Ga)Se2(液相CuxSe).在富Cu相-富In(Ga)相的演变过程中,依次发生以下相变:Cu(In,Ga)Se2(液相CuxSe)、Cu2(In,Ga)4Se7(或Cu(In,Ga)2Se3.5)、Cu(In,Ga)3Se5、Cu(In,Ga)5Se8.对这两个演变过程中薄膜的生长机理和结构特性进行了讨论.     

CdS薄膜的结构特性及其对Cu(In,Ga)Se2(CIGS)薄膜太阳电池的影响

报道了CdS薄膜的CBD法沉积及其结构特性,其中的水浴溶液包括硫脲、乙酸镉、乙酸铵和氨水溶液.研究了水浴溶液的pH值、温度、各反应物溶液的浓度和滴定硫脲与倾倒硫脲等基本工艺参数对CdS薄膜结构特性的影响.其中,溶液的pH值对CdS薄膜的特性起着关键的作用.XRD图显示了随着溶液pH值的变化,薄膜的晶相由六方相向立方相转变.CdS薄膜的这两种晶相对CIGS薄膜太阳电池性能的影响不相同.c-CdS(立方相的CdS)与CIGS之间的晶格失配和界面态密度分别为1.419%和8.507×1012cm-2,而h-CdS(六方相的CdS)与CIGS之间的晶格失配和界面态密度则分别为32.297%和2.792×1012cm-2.高效CIGS薄膜太阳电池需要的是立方相CdS薄膜.     

硒化温度对Cu(In, Al)Se2薄膜结构和光学性质的影响

采用了磁控溅射制备Cu-In-Al金属前驱体薄膜,后硒化快速退火得到铜铟铝硒(Cu(In,Al)Se2,CIAS)薄膜.研究了硒化温度对CIAS薄膜晶体结构和光学性质的影响.研究发现CIAS薄膜的晶体结构依赖于硒化温度,其禁带宽度随硒化温度升高发生红移.研究结果表明,CIAS薄膜的最佳硒化温度为540℃,其晶体结构为纯黄铜矿结构,禁带宽度为.34 eV,对应太阳电池理论最大效率的吸收层材料禁带宽度     

CdS薄膜的结构特性及其对Cu(In,Ga)Se2(CIGS)薄膜太阳电池的影响

报道了CdS薄膜的CBD法沉积及其结构特性,其中的水浴溶液包括硫脲、乙酸镉、乙酸铵和氨水溶液.研究了水浴溶液的pH值、温度、各反应物溶液的浓度和滴定硫脲与倾倒硫脲等基本工艺参数对CdS薄膜结构特性的影响.其中,溶液的pH值对CdS薄膜的特性起着关键的作用.XRD图显示了随着溶液pH值的变化,薄膜的晶相由六方相向立方相转变.CdS薄膜的这两种晶相对CIGS薄膜太阳电池性能的影响不相同.c-CdS(立方相的CdS)与CIGS之间的晶格失配和界面态密度分别为1.419%和8.507×1012cm-2,而h-CdS(六方相的CdS)与CIGS之间的晶格失配和界面态密度则分别为32.297%和2.792×1012cm-2.高效CIGS薄膜太阳电池需要的是立方相CdS薄膜.     

MgF2/Se薄膜封装层对OLED性能及寿命的影响

有机电致发光器件(OLEDs)在使用过程中,易受到 空气中水汽、氧气及其它污染物的影响从而导致其工作寿命降低。本文将具有良好光透过率 和热稳定性的MgF₂薄膜与在水汽和氧气中具有良好稳定性的Se薄膜通过真空蒸镀制成复 合薄膜作为OLEDs的封装层,以达到提高器件使用寿命的目的。器件各功能层蒸镀完成后, 保持真空度(3×10－4 Pa)不变,在阴极表面蒸镀MgF₂/Se薄 膜封装层。比较 了绿光OLED器件(器件结构为ITO/CuPc/NPB/Alq₃:C-545T/Alq ₃/LiF/Al)封装前后的亮度-电压-电流密度特性、电致发光光谱及寿命。研究 发现,经过MgF₂/Se封装后,器件的电流密度-电压特性、亮度和发光光谱几乎没 有受到影响,二者的光谱峰都在528 nm处,色坐标(CIE)分别为(0.3555,0.6131)和(0.3560,0.6104),只是起亮电压由3V变为4V;器件的寿命由原来的175h变为300h,提高了1.7倍 。因此,MgF₂/Se薄膜是一种有效的OLEDs无机薄膜封装层。     

膜厚对Ag-TiO2薄膜光学性能和光催化性能影响的研究

采用电子束沉积方法制备了Ag-TiO₂光催化剂 ,采用电子扫描显微镜(SEM)、X射线衍射仪(XRD)、透 射电镜(TEM)、紫外-可见(UV-Vis)光谱仪和原子力显微镜(AFM)等手段对薄膜的形貌、物 相 组成,吸收光谱和粗糙度进 行了表征。利用太阳光,以甲基橙(MO)为模拟污染物,考察光催化剂的光催化活性,探讨了薄 膜厚度对光催化 效率的影响。结果表明,在300℃温度下,所形成的薄膜 为无定形结构 ;当薄膜厚为570nm时,降解40days后,MO的降 解率达到55%。     

退火Cu2O薄膜的结构及光学特性

采用射频(RF)磁控溅射单质金属铜(Cu)靶, 在O₂和Ar的混合气氛下制备了Cu₂O薄 膜,并在N₂气氛下对预沉积的Cu₂O薄膜进行快速光热退火(RTA)处理,研究了 衬底温度及退火温度对Cu₂O 薄膜的生长行为、物相结构、表面形貌及光学性能的影响。结果表明,衬底温度在300℃以 下预沉积的Cu₂O薄膜 为非晶薄膜,退火处理对Cu₂O薄膜的结晶行为有明显影响,在N₂气氛下对Cu₂O薄膜进 行退火处理不影响薄膜的物 相结构;预沉积和退火Cu₂O薄膜在650nm以下波长范围内均有较强 吸收,吸收强度随退火温度的增加而增强,薄 膜在400nm以下波长范围内出现两个由缺陷引起的中间带(IB)吸收行 为,快速热退火处理不能减少或消除薄膜沉积 过程中形成的缺陷态;退火处理影响薄膜的光学带隙Eg,预沉 积薄膜经600℃退火处理,E_g值增大了 0.26eV。     

利用多光子电离显微术研究铜铟镓硒薄膜太阳电池的微纳米膜层结构

基于超短脉冲激光多光子电离显微成像原理,利 用平均功率50μW、脉冲重复频率1kHz的 50fs激光脉冲,对铜铟镓硒(CIGS)薄膜太阳电池进行深度扫描, 比较分析了单纯钠钙玻璃衬底、镀钼钠钙 玻璃和铜铟镓硒/钼膜层/钠钙玻璃三种不同结构样品飞秒激光电离辐射信号的差别。实验发 现,对应于不同膜 层材料的飞秒激光诱导的电离辐射信号强度明显不同,在钠钙玻璃中电离辐射信号的强度约 为空气本底的 20倍,在Mo背电极层信号强度约为钠钙玻璃衬底的50倍,而CIGS层则出现与其带隙相对应的吸收谷, 谷的强度与空气背景相同,利用多光子电离显微术对太阳电池进行逐点扫描可以对CIGS和Mo 背电极层 的成膜质量、吸收带隙和微纳结构进行精细研究。分析表明,超短脉冲多光子电离显微术对 不同物质边界处 的变化非常敏感,在具有多层结构的复杂器件的微观特性检测方面具有独特的优势。     

The effect of Mo back contact ageing on Cu(In,Ga)Se2 thin‐film solar cells

In this work, we investigate the effect of ageing Mo‐coated substrates in a dry and N₂ flooded cabinet. The influence was studied by preparing Cu(In,Ga)Se₂ solar cells and by comparing the electrical performance with devices where the Mo layer was not aged. The measurements used for this study were current–voltage (J‐V), external quantum efficiency (EQE), secondary ion mass spectroscopy (SIMS) and capacitance–voltage (C‐V). It was concluded that devices prepared with the aged Mo layer have, in average, an increase of 0.8% in efficiency compared with devices that had a fresh Mo layer. Devices with aged Mo exhibited a nominal increase of 12.5 mV of open circuit voltage, a decrease of 1.1 mA/cm⁻² of short circuit current and a fill factor increase of 2.4%. Heat treatment of fresh Mo layers in oxygen atmosphere was also studied as an alternative to ageing and was shown to provide a similar effect to the aged device's performance. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Impact of compositional grading and overall Cu deficiency on the near‐infrared response in Cu(In,Ga)Se2 solar cells

Highly efficient thin film solar cells based on co‐evaporated Cu(In,Ga)Se₂ (CIGS) absorbers are typically grown with a [Ga]/([Ga] + [In]) (GGI) gradient across the thickness and a Cu‐poor composition. Upon increasing the Cu content towards the CIGS stoichiometry, lower defect density is expected, which should lead to increased absorption in the near‐infrared (NIR), diffusion length and carrier collection. Further, optimization of the GGI grading is expected to increase the NIR response. In this contribution [Cu]/([In] + [Ga]) (CGI) values are increased by shortening the deposition stage after the first stoichiometric point. In order to obtain comparable Ga contents at the interface for proper band alignment, the front GGI gradings were actively modified. With a relative CGI increase of 7%, we observe an increased photocurrent, originating from an improved NIR external quantum efficiency response. By characterizing the modified absorber properties by reflection‐transmission spectroscopy, we attribute the observed behavior to changes in the optical properties rather than to improved carrier collection. Cu‐dependent modifications of the NIR‐absorption coefficients are likely to be responsible for the variations in the optical properties, which is supported by device simulations. Adequate re‐adjustments of the co‐evaporation process and of the alkali‐fluorides post‐deposition treatments allow maintaining V_oc and FF values, yielding an overall increase of efficiency as compared to a reference baseline. © 2016 The Authors. Progress in Photovoltaics : Research and Applications published by John Wiley & Sons Ltd.     

Structural Characteristic of CdS Thin films and Their Influence on Cu(in,Ga)Se2(CIGS) Thin Film Solar Cell

Deposition and structural characteristics of cadmium sulfide (CdS) thin films by chemical bath deposition (CBD) technique from a bath containing thiourea,cadmium acetate,ammonium acetate and ammonia in an aqueous solution are reported.Researches are made on the influence of the fundamental parameters including pH,temperature,and concentrations of the solution involved in the chemical bath deposition of CdS and titration or dumping of the thiourea solution on the structure characteristic of CdS thin films.The pH of the solution plays a vital role on the characteristic of the CdS thin films.The XRD patterns show that the change in the pH of the solution results in the change in crystal phase from predominant hexagonal phase to predominant cubic phase.The CdS thin films with the two different crystal phases have different influences on CIGS thin film solar cells.The crystal mismatch and the interface state density of the cCdS(cubic phase CdS) and CIGS are about 1.419% and 8.507×1e12cm－２ respectively,and those of the h-CdS(hexagonal phase CdS) and CIGS are about 32.297% and 2.792×1e12cm－２ respectively.It is necessary for high efficiency CIGS thin film solar cells to deposit the cubic phase CdS thin films.     

Non‐destructive optical analysis of band gap profile,crystalline phase,and grain size for Cu(In,Ga)Se2 solar cells deposited by 1‐stage, 2‐stage,and 3‐stage co‐evaporation

Cu(In,Ga)Se₂ (CIGS) thin films co‐evaporated by 1‐stage, 2‐stage, and 3‐stage processes have been studied by spectroscopic ellipsometry (SE). The disappearance of a Cu_2‐xSe optical signature, detected by real time SE during multistage CIGS, has enabled precise endpoint control. Band gap energies determined by SE as depth averages show little process variation for fixed [Ga]/([In] + [Ga]) atomic ratio, whereas their broadening parameters decrease with increasing number of stages, identifying successive grain size enhancements. Refined SE analysis has revealed band gap profiling only for 3‐stage CIGS. Solar cells incorporating these absorbers have yielded increased efficiencies in correlation with phase control, grain size, and band gap profiling. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of the Cu(In,Ga)Se2 thickness and Ga grading on solar cell performance

Thin‐film solar cells with Cu(In,Ga)Se₂ (CIGS) absorber layers ranging from 1.8 to 0.15 μm in thickness were fabricated by co‐evaporation, with both homogeneous and Ga/(Ga + In) graded composition. The absorption of the CIGS layers was determined and compared with corresponding QE measurements in order to obtain the optical related losses. The material characterization included XRD as well as cross‐sectional SEM analysis. Devices with CIGS layers of all thicknesses were fabricated, and down to 0.8–1 μm they showed a maintained high performance (η ∼ 15%). When the CIGS layer was further reduced in thickness the loss in performance increased. The main loss was observed for the short‐circuit current, although the loss was not only due to a reduced absorbance. The open‐circuit voltage was essentially not affected by the reduction of the CIGS thickness, while the fill factor showed a slight decrease. The fill factor loss was eliminated by introducing a Ga/(Ga+In) graded CIGS, which also resulted in an increased open‐circuit voltage of 20–30 mV for all CIGS thicknesses. Device results of 16.1% efficiency at 1.8 μm CIGS thickness, 15.0% at 1.0 μm and 12.1% at 0.6 μm (total area without anti‐reflective coating) were achieved. Copyright © 2002 John Wiley & Sons, Ltd.     

Titanium wire engineering and its effect on the performance of coil type cylindrical dye sensitized solar cells

This paper reports a comparative study of the photovoltaic characteristics of titanium (Ti) metal wires with different diameter and surface treatments towards their utilization as photoanodes for coil-based dye-sensitized solar cells. The surface property of the Ti wire, especially oxidized overlayer and surface treatments have been found to greatly influence the adhesion as well as optimum electrical contact between coated nanoporous titanium oxide (TiO₂) and Ti-wires. Implication of adhesion of nanoporous TiO₂ on the titanium wire and its influence on photovoltaic performance was analyzed using electrochemical impedance spectroscopy. Results of X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy reveals the formation of anatase TiO₂ nanosheets after the H₂O₂ surface treatment on the titanium wire resulting into enhancement in the extent of dye loading leading to enhanced photoconversion efficiency of 4.71% under simulated solar irradiation.