The influence of acid treatment of TiO2 porous film electrode on photoelectric performance of dye-sensitized solar cell

A dye-sensitized solar cell (DYSC) was assembled by adsorbing cis-dithiocyanato-bis (2,2^′-bipyridyl-4,4^′-dicarboxylate) ruthenium (II) onto TiO₂ porous film. The influence of acid treatment of TiO₂ electrode with different kinds and concentrations on the photoelectric performance of DYSC was investigated. It was found that DYSC had better photoelectric performance when the TiO₂ electrode was treated by hydrochloric acid than that by sulfuric acid, nitric acid and phosphoric acid. When the concentration of hydrochloric acid to treat TiO₂ electrode increases from 0 to 0.10 M, the fill factor of DYSC increases, the short-circuit current decreases, the open-circuit photovoltage increases and the absorption amount for TiO₂ porous film to dye molecules decreases. The acid treatment of TiO₂ electrode provides useful information on the mechanism of energy conversion of DYSC.     

染料敏化太阳能电池光阳极的优化与性能研究

对染料敏化太阳能电池（DSSC）光阳极的制作工艺进行优化设计,在光阳极初始默认的制作工艺条件下,分别对影响DSSC光电性能的光阳极活性面积、TiO₂薄膜厚度、是否添加散射层、TiO₂薄膜烧结温度、化学处理方法和TiCl₄浓度影响因素逐一进行考察,最终确定了光电极的最佳制作工艺：光阳极活性层面积为0.4 cm × 0.4 cm,TiO₂薄膜厚度为19 μm,并加散射层,TiO₂薄膜电极的烧结温度为T₁ = 525℃、二次烧结温度为T₂ = 500℃,采用0.1 mol/L的TiCl₄水溶液进行化学处理,获得短路电流密度19.45 mA/cm²,光电转换效率8.42%。此制作工艺方法简单、光谱特性好、光电转换效率高,有利于DSSC的结构优化与推广应用。     

Novel device structure for Cu(In,Ga)Se2 thin film solar cells using transparent conducting oxide back and front contacts

Cu(In_1−xGa_x)Se₂ (CIGS)-based thin film solar cells fabricated using transparent conducting oxide (TCO) front and back contacts were investigated. The cell performance of substrate-type CIGS devices using TCO back contacts was almost the same as that of conventional CIGS solar cells with metallic Mo back contacts when the CIGS deposition temperatures were below 500 °C for SnO₂:F and 520 °C for ITO. CIGS thin film solar cells fabricated with ITO back contacts had an efficiency of 15.2% without anti-reflection coatings. However, the cell performance deteriorated at deposition temperatures above 520 °C. This is attributed to the increased resistivity of the TCO’s due to the removal of fluorine from SnO₂ or undesirable formation of a Ga₂O₃ thin layer at the CIGS/ITO interface. The formation of Ga₂O₃ was eliminated by inserting an intermediate layer such as Mo between ITO and CIGS. Furthermore, bifacial CIGS thin film solar cells were demonstrated as being one of the applications of semi-transparent CIGS devices. The cell performance of bifacial devices was improved by controlling the thickness of the CIGS absorber layer. Superstrate-type CIGS thin film solar cells with an efficiency of 12.8% were fabricated using a ZnO:Al front contact. Key techniques include the use of a graded band gap Cu(In,Ga)₃Se₅ phase absorber layer and a ZnO buffer layer along with the inclusion of Na₂S during CIGS deposition.     

Physicochemical properties and photocatalytic hydrogen evolution of TiO2 films prepared by sol–gel processes

Anatase TiO₂ films were obtained on glass substrates using a sol–gel method using titanium isopropoxide as a precursor. The thickness of the film was about 140 nm for one coating, and the thickness is controlled by the number of coating cycles. The spectra of UV-VIS absorption indicated that the absorption edge of the TiO₂ films is ca. 385 nm, corresponding to the band gap energy of 3.20 eV. We obtained TiO₂ films having a high activity for the hydrogen evolution from photocatalytic water cleavage. By loading with 0.3 wt% Pt rate of hydrogen production increases. No influence of film thickness and calcination temperature on the photocatalytic property is observed.     

Importance of the band gap energy and flat band potential for application of modified TiO2 photoanodes in water photolysis

The influence on water photolysis of two important parameters of the electronic structure of photocatalytic semiconductors: the forbidden band gap, E_g, that decides about the absorption spectrum and the flat band potential, V_Fb, that affects the recombination probability, was studied. The photoelectrochemical experiments were performed in a three-electrode cell PEC with a TiO₂ thin film photoanode immersed in liquid electrolyte of variable pH. Titanium dioxide photoanodes doped with chromium (up to 16 at.%) and tin (up to 50 at.%) were prepared by rf reactive sputtering. Different methods of flat band potential determination: Mott–Schottky plots and photocurrent versus voltage characteristics were used. The energy band gap was derived from the spectrophotometric measurements of optical transmittance and reflectance coefficients of thin films. For TiO₂ + 7.6 at.% Cr high and negative flat band potential V_Fb = −0.72 eV (at pH 4) has been found but the recombination time τ = 8 s was the shortest of all TiO₂ modifications. Despite additional absorption feature at about 2.8 eV, i.e., at wavelength corresponding to visible range of the light spectrum, the photoconversion efficiency of TiO₂ + 7.6 at.% Cr was found to be much smaller (η_c = 0.1%) than that of undoped TiO₂ (η_c = 1.8%) and TiO₂ doped with 8 at.% of Sn (η_c = 1.0%).     

染料敏化太阳能电池电子传输的数值模拟研究

基于电子传输的扩散理论建立了染料敏化太阳能电池(DSSC)的连续性方程,使用适合于二氧化钛(TiO₂)作为光阳极的内部参数,对DSSC电子注入和传输的内在机理进行研究。分别考查温度、TiO₂膜厚、电子寿命、电子扩散系数、光照强度、吸收系数等因素对DSSC光电性能的影响,为DSSC性能的改进及光电转换效率的提高提供理论指导。     

Large area CIGS2 thin film solar cells on foils: nucleus of a pilot plant

In earlier research, conversion efficiency of 10.4% (AM1.5) and 9.9% (AM0) has been achieved on small area CuIn_xGa_1−xS₂ (CIGS2) solar cell on 127 μm thick stainless steel substrate. The area of research is mainly focused on studying CIGS2 thin films as solar cell absorber material and growing high efficiency cells on ultralightweight and flexible metallic foils such as 127 μm thick stainless steel and SiO₂ coated 25 μm thick Ti foils. This paper presents the scaling up process of CIGS2 thin film substrate from 2.5 × 2.5 cm² to 10 × 10 cm². Initial scaling up efforts focused on achieving uniform thickness and stress-free films. Process of scaling up consisted of refurbishment of selenization/sulfurization furnace, design and fabrication of scrubber and enlargement of new CdS deposition setup. The scaling up from 2.5 × 2.5 cm² to 10 × 10 cm² substrate size has laid the foundation for PV Materials Lab of Florida Solar Energy Center becoming the nucleus of a pilot plant.     

上转换材料TiO2∶Er3+/Yb3+/Li+的制备及其在玻璃盖板中的应用

采用溶胶凝胶法和旋转镀膜法制备Er³⁺/Yb³⁺/Li⁺掺杂TiO₂胶体和薄膜,确定上转换材料最优制备方案为n(乙酰丙酮)∶n(C₁₆H₃₆O₄Ti∶H₂O)∶n(异丙醇)∶n(Er(NO₃)₃·5H₂O)∶n(Yb(NO₃)₃·5H₂O)∶n(LiNO₃)=1∶3∶9∶70∶0.12∶0.60∶0.15(物质的量之比),水的滴加速率为10 s/滴,溶液pH值为2～3,溶胶呈透明均匀淡黄色。吸收光谱在近红外区峰值明显。可见光透光率最高可达94.42%,较普通玻璃提高1%～2%。光伏组件通过光电转换效率测量系统进行检测,玻璃盖板镀膜后光伏组件的光电转换效率从16.5%升至17.2%,增加约0.7%。研究结果表明,该薄膜可提高玻璃盖板透光率,扩大光伏组件光谱吸收范围...     

Austenitic stainless steels in high temperature phosphoric acid

Austenite 316 L, 317 L, and 904 L stainless steels were investigated in 98% H₃PO₄ at 170 °C and they experienced passivation regardless of the purged gas. When polarized at 0.1 V (hydrogen) and 0.7 V (air) (phosphoric acid fuel cell (PAFC) environments), currents at the level of mA cm⁻² were observed. Compared to carbon composite under identical conditions, 904 L showed lower currents while 316 L and 317 L showed much higher currents.

X-ray photoelectron spectroscopy (XPS) depth profiles indicated that the surface film of the fresh steels consists of a Fe-oxide-rich outer layer and a Cr-oxide-rich inner layer. After being polarized in the PAFC environments, the Fe-oxide layer was selectively dissolved and Cr-oxide dominated the passive film. Phosphorus was incorporated into the film during the process, thus the chemical composition of the passive film differed from those formed in the polymer electrolyte membrane fuel cell (PEMFC) environments. The thicknesses of the stainless steels in the passive films in PAFC environments were estimated.     

An effective use of nanocrystalline CdO thin films in dye-sensitized solar cells

Thin films of cadmium oxide (CdO) were synthesized by layer-by-layer deposition method on indium doped tin oxide (ITO) substrates. Post-deposition annealing at 250 °C for 24 h produced pure phase CdO films by removal of trace amount of cadmium hydroxide, as confirmed from X-ray diffractogram. First time employment of CdO in place of TiO₂ in dye-sensitized solar cells is reported to check feasibility and cell performance. A dye-sensitized nanocrystalline CdO photo-electrode was obtained by adsorbing cis-dithiocyanato (4,4′-dicarboxylic acid-2,2′-bipyridide) ruthenium (II) (N3) dye by keeping at 45 °C for 20 h. The efficiency of dye-sensitized nanocrystalline CdO thin film solar cell was increased from 0.24% to 2.95% due to dye adsorption. This must be highest reported conversion efficiency for other metal oxides than TiO₂based dye-sensitized solar cells.     

Chemical bath deposition of Cds buffer layer for GIGS solar cells

We investigated the chemical bath deposition of US thin flims on the Cu(In,Ga)Se₂ (GIGS) absorber layers and glasses. The process of the chemical bath deposition of US layer affected the performance of the CIGS solar cells. The CdS layers were deposited on the CIGS film from CdI₂, thiourea (NH₂CSNHn₂) and ammonia solutions. The influence of pH on the chemical bath deposition process was studied. The surfaces of the US films were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The compositions of the obtained CdS layers were analyzed by Auger electron spectroscopy (AES). The performance of the CIGS solar cells was discussed on the basis of the characteristics of the chemical bath deposited layer. We have successfully fabricated a high-efficiency CIGS solar cell with an efficiency of 17% using a US layer with stoichiometric composition.     

Quasi-solid-state dye-sensitized solar cells employing ternary component polymer-gel electrolytes

Ternary component polymer-gel electrolytes are designed to facilitate ion transport in a highly viscous medium and utilize incident light more efficiently in dye-sensitized solar cells (DSSCs). Polyethers with multiple molecular size distributions are employed as solvents and TiO₂ nanoparticles as a filler to prepare the polymer-gel electrolytes. The ion transport properties of the electrolytes are systematically investigated using electrochemical analyses such as ion conductivity and diffusion coefficient measurements. The influences of the electrolyte components on the electron transport in photoanodes are also investigated by measuring the laser-induced photovoltage and photocurrent transient response, incident photon-to-current efficiency (IPCE), and current–voltage (J–V) curves. The optimized polymer-gel electrolyte results in greatly enhanced energy conversion efficiency (i.e., 7.2% at 1 sun) due to the significantly improved ion transport and good light-scattering effect of the nanofillers.     

High-performance polypyrrole nanoparticles counter electrode for dye-sensitized solar cells

Polypyrrole (PPy) nanoparticle was synthesized and coated on a conducting FTO glass to construct PPy counter electrode used in dye-sensitized solar cell (DSSC). Scanning electron microscope images show that PPy with porous and particle diameter in 40–60 nm is covered on the FTO glass uniformly and tightly. Cyclic voltammograms of I₂/I⁻ system measurement reveals that the PPy electrode has smaller charge-transfer resistance and higher electrocatalytic activity for the I₂/I⁻ redox reaction than that Pt electrode does. Overall energy conversion efficiency of the DSSC with the PPy counter electrode reaches 7.66%, which is higher (11%) than that of the DSSC with Pt counter electrode. The excellent photoelectric properties, simple preparation procedure and inexpensive cost allow the PPy electrode to be a credible alternative used in DSSCs.     

锑基硫属化合物半导体及太阳电池

锑基硫属化合物是一类性质稳定、环境友好、元素含量丰富、带隙连续可调、光电性质优异的半导体材料,包括硒化锑（Sb₂Se₃）、硫化锑（Sb₂S₃）以及硒硫化锑[Sb₂(S,Se)₃]等。其中,Sb₂(S,Se)₃的带隙和太阳光谱的匹配度较高,比较适合作为太阳电池的光吸收层材料。以Sb₂(S,Se)₃为光吸收层的太阳电池取得了10% 的认证能量转换效率,显示了锑基硫属化合物太阳电池的巨大潜力。本文详细阐述了锑基硫属化合物的材料及光电特性、薄膜制备工艺及缺陷特性。结合近年来锑基硫属化合物太阳电池的研究进展,提出进一步提高锑基硫属化合物太阳电池性能的方向和策略。     

紫外光下Ag掺杂TiO2薄膜基底对VO2相转变温度的影响

利用溶胶−凝胶法和浸渍提拉技术制备了不同结构银掺杂二氧化钛薄膜为基底材料的VO₂薄膜,考察了Ag分级配置的二氧化钛薄膜基底材料对VO₂薄膜相变温度的影响。在紫外灯照射下测试面内电阻随温度,电压随时间的变化,结果表明基底材料为Ag分级配置的VO₂/TiO₂薄膜相变温度点明显降低。这可能是由于光照条件下空穴载流子从基底材料注入到VO₂薄膜导致相变温度点偏移。因此,不同结构银掺杂二氧化钛薄膜为基底材料的VO2薄膜能够根据环境温度和太阳光线变化而应用于光热致变色智能窗。     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.     

PL and PLE studies of KMgF3:Sm crystal and the effect of its wavelength conversion on CdS/CdTe solar cell

We studied the effect on conversion efficiency of a CdS/CdTe solar cell by applying a wavelength conversion of a rare earth ion. Both photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the Sm-doped KMgF₃ crystal were investigated. As a result, we found that both the divalent and the trivalent Sm ions coexist in the grown KMgF₃ crystals. Also, all the PLE spectra below 500 nm were effectively converted to PL spectra above 540 nm and the solar cell possessed a high spectral response. The quantum efficiency of Sm ions was estimated to be 0.84 from the comparison of the experimental curve with the calculated one for the increased spectral response below 500 nm. When a thin disc crystal of KMgF₃:Sm was placed on the top of CdS/CdTe solar cell as a precursor for wavelength conversion, both the maximum output power and the conversion efficiency increased by 5% as compared with the case of a pure KMgF₃ crystal.     

CuInS2 based thin film photovoltaics

A fabrication process for CuInS₂ thin film solar cells, based on sulfurization of Cu/In bilayers, is described. The process is investigated by in situ energy dispersive X-ray diffraction for phase identification as a function of process time. It is found that Raman spectroscopy is very convenient and reliable in assessing the quality of CuInS₂ produced by this sequential process. Good quality CuInS₂ films efficiently collect charge carriers generated by the incident sunlight. The solar-to-electric conversion efficiency limitations of state-of-the-art CuInS₂ based devices are discussed using a comparison with device simulation. The module design is laid down and arguments for the up-scaling potential of this new type of solar cell are presented.     

XPS analysis of CdS/CuInSe2 heterojunctions

CdS/CuInSe₂ (CIS) heterojunctions were investigated by XPS analysis. An In-excess layer which may form an ordered vacancy compound (OVC) was present at the as-deposited CIS surface and it remained after chemical bath deposition of a CdS layer. The In-excess layer was removed by preferential etching with NH₃ aqueous solution. This result implies that the surface of the as-deposited CIS film was converted from the OVC with n-type conductivity into the CIS with p-type by NH₃ treatment. The conduction band offsets at the CdS/p-CIS and CdS/n-OVC were determined to be 1.0 and 0.3 eV, respectively. The CIS solar cells fabricated with n-OVC surface layer exhibited higher cell efficiencies than those fabricated with p-CIS surface layer.     

Promising alloys for intermediate-temperature solid oxide fuel cell interconnect application

The formation of a low Cr-volatility and electrically conductive oxide outer layer atop an inner chromia layer via thermal oxidation is highly desirable for preventing chromium evaporation from solid oxide fuel cell (SOFC) metallic interconnects at the SOFC operation temperatures. In this paper, a number of ferritic Fe–22Cr alloys with different levels of Mn and Ti as well as a Ni-based alloy Haynes 242 were cyclically oxidized in air at 800 °C for twenty 100-h cycles. No oxide scale spallation was observed during thermal cycling for any of these alloys. A mixed Mn₂O₃/TiO₂ surface layer and/or a (Mn, Cr)₃O₄ spinel outer layer atop a Cr₂O₃ inner layer was formed for the Fe–22Cr series alloys, while an NiO outer layer with a Cr₂O₃ inner layer was developed for Haynes 242 after cyclic oxidation. For the Fe–22Cr series alloys, the effects of Mn and Ti contents as well as alloy purity on the oxidation resistance and scale area specific resistance were evaluated. The performance of the ferritic alloys was compared with that of Haynes 242. The mismatch in thermal expansion coefficient between the different layers in the oxide scale was identified as a potential concern for these otherwise promising alloys.