Preparation of Gd_2O_3 :Eu~(3+) downconversion luminescent material and its application in dye-sensitized solar cells

Gd₂O₃ :Eu³⁺ downconversion luminescent powder was prepared using the homogeneous precipitation method. Its optical properties were analyzed and it was introduced into a dye-sensitized solar cell （DSSC）. As a luminescence medium, Gd₂O₃ :Eu³⁺ improved light harvesting via conversion luminescence and increased the photocurrent of the DSSC. As a p-type dopant insulating rare earth oxides form an energy barrier, and the Gd₂O₃ :Eu³⁺ elevated the energy level of the oxide film and increased the photovoltage. The photoelectric conversion efficiency for a DSSC with Gd₂O₃ :Eu³⁺ doping （6 : 100） reached 7.01%, which was 17.4% higher than the photoelectrical conversion efficiency of a DSSC without Gd 2 O 3 :Eu 3+ doping.     

A Novel Polymer Electrolyte Using In-situ Quanternization for All Solid-state Dye-sensitized Solar Cell

1 Introduction Dye-sensitized solar cells (DSSCs) with a mesoporous network of interconnected TiO2 nanocrystals have attracted wide-spread scientific and technological interest over the past decades due to its low cost and high energy conversion efficiency. Meantime, it also has been considered as potential alternative to conventional photovoltaic devices. In 2001, Gratzel group constructed such kind of DSSC with the conversion efficiency of more than 11%[1]. But this system uses liquid electrolyte with the disadvantages of fluity and volatility, which reduces the long-term stability and increases difficulties in sealing the device.     

Recent Advances in High Efficiency Solar Cells

1 Results The conversion efficiency of sunlight to electricity is limited around 25%,when we use single junction solar cells. In the single junction cells,the major energy losses arise from the spectrum mismatching. When the photons excite carriers with energy well in excess of the bandgap,these excess energies were converted to heat by the rapid thermalization. On the other hand,the light with lower energy than that of the bandgap cannot be absorbed by the semiconductor,resulting in the losses. One way of reducing these losses is fabricating tandem or stacked solar cells. Merely stacking the more number of cells with different bandgap can increase the conversion efficiency. III-V compound multi-junction solar cells,such as InGaP/GaAs/Ge,have the potential for achieving high conversion efficiencies that are promising for space and terrestrial applications. One of the important issues for realizing the high conversion efficiency is the optically and electrically low-loss interconnection of each sells. A degenerately impurity doped tunnel junction,which is thin and wide-bandgap,is an attractive one,and a double hetero structure is useful for preventing impurity diffusion during the overgrowth of the top cell. Another issue is a lattice matching. Since there is a slightly difference in the lattice constant between Ge substrate and GaAs,the misfit dislocations are generated in thick GaAs layers and the electrical properties degrade. To prevent this problem,InGaAs is applied as a middle cell material,which is lattice matching to the Ge substrate. So far,the conversion efficiency of InGaP/InGaAs/Ge has been improved up to 29%-30% (AM0) and 31.7% (AM1.5G). The concentrator cells achieved the higher conversion efficiency up to 40.7% under 240 suns. For realizing a future multi-junction solar cell with ultra-high performance,InGaAsN and related materials are investigated,because it can be grown lattice matched to GaAs with a band gap in the range of 0.9-1.4 eV. When we adopt the InGaP/GaAs/InGaAsN/Ge structure as a four-junction solar cell,the efficiency over 40% (AM1.5G) will be expected. However,the minority carrier diffusion length in the present InGaAsN crystal is too short to realize the tandem solar cells with the expected high performance. To solve this problem,we have been developing the chemical beam epitaxy (CBE) method for achieving InGaAsN with good quality. The films are grown using organic gas molecules as sources under a high vacuum condition (10-2 Pa). Because of the ultra low pressure,the reactions between the source gases in the gas phase are suppressed and the chemical reactions occur only on a growing surface,which allow using active source gases that decompose at low temperatures. GaAsN thin films are grown using monomethylhydrazine as a N source with narrow X-ray diffraction peaks at growth temperatures in the 380-420 ℃ range. In the present talk,we will review the progress of high conversion efficiency tandem-solar cells and discuss some of our recent results.     

Application of upconversion luminescence in dye-sensitized solar cells

An upconversion luminescence powder TiO2:(Er3+,Yb3+) is prepared by a hydrothermal method and used to fabricate dye-sensitized solar cell (DSSC).The TiO2:(Er3+,Yb3+) powder undergoes upconversion luminescence,converting infrared light which the dye can not absorb into visible light with wavelengths of 510-700 nm which the dye can absorb,increasing the photocurrent of the DSSC.TiO2:(Er3+,Yb3+) also acts as a p-type dopant,heightening the Fermi level of the oxide film,which increases the photovoltage of the DSSC.The best performance of the DSSC is found when the ratio of TiO2/luminescence powder is 1/3 in the luminescence layer.Under simulated solar irradiation of 100 mW cm-2 (AM 1.5),the DSSC containing TiO2:(Er3+,Yb3+) doping achieves a light-to-electricity energy conversion efficiency of 7.28% compared with 6.41% for the undoped DSSC.     

TiO2 nanotube arrays and TiO2-nanotube-array based dye-sensitized solar cell

To substitute the non-regular nano-crystalline semiconductor for a novel kind of ordered microstructure is a very important aspect in the domain of dye-sensitized solar cell. One of the researching hot- spots is the highly-ordered TiO2 nanotube architecture. As a new type of titania nano-material, titania nanotube arrays have drawn extraordinary attention due to its distinctive morphology, notable photo-electrical and hydro-sensitive performance. At 100% sun the new kind of TiO2 nanotube arrays solar cell exhibits an overall conversion efficiency of 5.44%. This paper introduces the preparation methods of titania nanotube arrays, the existing problems and recent progress in titania nanotube arrays solar cell.     

Fabrication and characterization of TiO2 -based dye-sensitized solar cells

Dye-sensitized solar cells TiO_2 with were fabricated.The phase composition and microstructures of the solar cells were examined by X-ray diffractometry and transmission electron microscopy,and the energy levels of the present solar cells were also discussed.The results show that a solar cell mixed with xylenol orange and rose Bengal shows a higher conversion efficiency compared to solar cells with a single dye.An introduction of amorphous TiO_2 layers results in an improvement of the conversion efficien...     

Low temperature fabrication of high performance and transparent Pt counter electrodes for use in flexible dye-sensitized solar cells

High performance Pt counter electrode is prepared by using vacuum thermal decomposition at a relatively low (120℃) temperature on a flexible polyethylene naphthalate substrate coated with indium-doped tin oxide for use in flexible dye-sensitized solar cells.The obtained Pt counter electrode shows a good chemical stability,high light transmittance,and high electrocatalytic activity for the I3-/I-redox reaction.The energy conversion efficiency of a flexible dye-sensitized solar cell based on the prepared Pt counter electrode and a TiO 2 /Ti photoanode reaches 5.14% under a simulated solar light irradiation with intensity of 100 mW cm-2.     

Flexible dye-sensitized solar cell based on PCBM/P3HT heterojunction

Using blend heterojunction consisting of C60 derivatives [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene) (P3HT) as charge carrier transferring medium to replace I3–/I– redox electrolyte,a novel flexible dye-sensitized solar cell (DSSC) is fabricated.The characterization of infrared spectra and ultraviolet-visible spectra shows that the PCBM/P3HT heterojunction has not only the absorption in ultraviolet light for PCBM,but also the absorption in visible and near infrared light for P3HT,which widens the photoelectric response range for DSSC.The influence of PCBM/P3HT mass ratio on the performance of the solar cell is discussed.Under 100 mW cm–2 (AM 1.5) simulated solar irradiation,the flexible solar cell achieves a lightto-electric energy conversion efficiency of 1.43%,open circuit voltage of 0.87 V,short circuit current density of 3.0 mA cm–2 and fill factor of 0.54.     

Fabrication of a TiO2-P25/(TiO2-P25+TiO2 nanotubes) junction for dye sensitized solar cells

The dye sensitized solar cell（DSSC）, which converts solar light into electric energy, is expected to be a promising renewable energy source for today’s world. In this work, dye sensitized solar cells, one containing a single layer and one containing a double layer, were fabricated. In the double layer DSSC structure, the under-layer was TiO₂-P25 film, and the top layer consisted of a mixture of TiO₂-P25 and TiO₂ nanotubes. The results indicated that the efficiency of the DSSC with the double layer structure was a significant improvement in comparison to the DSSC consisting of only a single film layer. The addition of TiO₂-P25 in the top layer caused an improvement in the adsorption of dye molecules on the film rather than on the TiO₂ nanotubes only. The presence of the TiO₂ nanotubes together with TiO₂-P25 in the top layer revealed the enhancement in harvesting the incident light and an improvement of electron transport through the film.     

Preparation of porous nanocrystalline TiO2 electrode by screen-printing technique

Different paste has been used for preparing porous TiO2 thin film by screen-printing technique, the main component of it comes from commercial TiO2 P25 power. The dye-sensitized solar cell based on this TiO2 thin film without further chemical treatments exhibits high overall conversion efficiency of 5.81%―6.70%, even with low TiO2 content and thin film thickness. The experimental repeatability is nice and the properties of the films are uniform.     

基于含氮、硫元素苯衍生物的有机染料敏化剂的理论研究

采用密度泛函(DFT)和含时密度泛函(TD-DFT)理论方法计算了以苯及其衍生物作为π共轭桥的染料分子的基态和激发态的微观性质.研究结果表明,与参考敏化剂P0相比,3种新型敏化剂P1、P2和P3的基态几何结构和前线轨道分布与之十分相似.采用CPCM-TD-BHandHLYP/6-31+G(d)方法,模拟染料分子P1在二氯甲烷溶液中的最大吸收波长为502nm,比P0吸收峰显著红移.利用Marcus理论,经过近似计算发现,与其他敏化剂相比,P1分子间电荷传输速率(Ket)最快.因此,P1应该可以作为有希望的敏化剂应用于染料敏化太阳能电池(DSSC),而且其能量转化效率(η)应该高于以P0为染料的DSSC的效率.     

A new improved structure of dye-sensitized solar cells with reflection film

DYE-SENSITIZED NANOCRYSTALLINE SOLAR CELLS (DSSC), RECENTLY DEVELOPED BY MICHAEL GR?TZEL[1], HAVE BEEN ATTRACTING CONSIDERABLE ATTENTIONS BECAUSE OF ITS HIGH EFFICIENCY, SIMPLE FABRICATION PROCESS AND LOW FABRICA- TION COST[2]. TYPICAL DSSC[3] IS BASED ON A SANDWICH STRUCTURE, WHICH CONSISTS OF TWO GLASS PLATES WITH A TRANSPARENT CONDUCTING OXIDE (TCO) COATING AS SUBSTRATE. O…     

分布式静止同步串联补偿器抑制次同步谐振机理研究

针对柔性交流输电(FACTS)领域中的一种新装置——分布式静止同步串联补偿器(DSSC),在实现其潮流调节功能的基础上,首次从频域的角度研究了DSSC特性,得到了DSSC的频率-阻抗分布曲线,既为DSSC影响次同步谐振的机理研究提供了理论依据,也为其他FACTS装置的研究提供了新的思路.进一步,采用测试信号法,研究了DSSC对一个串联电容补偿系统的电气阻尼特性的影响,结果表明,DSSC的串入使得系统的谐振点频率发生偏移,电气负阻尼绝对值显著减小,证明DSSC对于次同步谐振具有抑制作用.     

人工光合成机理的时空分辨光谱研究进展

 综述了时空分辨光谱技术在人工光合成机理研究中的主要结果和最新进展，揭示了人工光合成中光生电子和空穴的分离、复合和反应等过程，利用成像光谱直接观测光生电荷的空间分布及其作用规律。时空分辨光谱的表征结果很好地解释了催化剂晶相、助催化剂的担载、相结结构的构筑、晶面调控等策略在光电催化过程中的作用机制。     

Influence of nanostructure on the device performance and charge recombination dynamics of P3HT:PCBM solar cells

In this paper,we investigated the recombination dynamics of photogenerated charge carriers in a poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C 61-butyric acid methyl ester(PC 61 BM) blend system with donor-acceptor ratio of 1:1 before and after solvent annealing treatment.The technique of transient photocurrent and photovoltage measurements were used,and charge carriers were photogenerated by a 7 ns laser pulse at room temperature(298 K).In transient photocurrent measurement,we observed some differences in the saturation extracted charge in P3HT:PCBM solar cells with different power efficiencies.In addition,the bimolecular recombination coefficient is found to be 3.5×10-13 cm 3 s-1 for annealed devices,while 9.5×10-12 cm3 s-1 for as-cast devices.In the transient photovoltage measurement,we found that the photovoltage decay can be fitted by power-law equation at long time scale.The exponent parameter is 2.6 for annealed devices,which can be described as trap-free bimolecular recombination;is 1.76 for as-cast device due to the trap-limited bimolecular recombination.These experimental results indicate that the nanomorphology of active layer indeed have influence on charge carriers dynamics in P3HT:PCBM blend systems.     

用背反射提高染料敏化太阳电池光吸收的研究

介绍了一种提高染料敏化太阳电池光吸收的背反射结构,以解决染料在长波范围吸光能力差的缺点。用P25纳米TiO2粉和水热法两种不同工艺制备了电池。透过光谱测试表明,两种工艺制备的电池对长波范围的光都没有充分利用,水热法制备的电池更透明。太阳模拟器测试结果表明,用银反光膜作为电池的背反射结构,增加了染料对长波范围内的光吸收,显著提高了电池的光电转换效率。P25粉工艺制备的电池效率提高了11.4%,水热法工艺制备的电池效率提高了22%。     

人工光合成机理的时空分辨光谱研究进展

 综述了时空分辨光谱技术在人工光合成机理研究中的主要结果和最新进展，揭示了人工光合成中光生电子和空穴的分离、复合和反应等过程，利用成像光谱直接观测光生电荷的空间分布及其作用规律。时空分辨光谱的表征结果很好地解释了催化剂晶相、助催化剂的担载、相结结构的构筑、晶面调控等策略在光电催化过程中的作用机制。     

低聚3-噻吩甲酸对纳晶TiO_2电极的敏化

通过光照化学聚合法合成低聚3-噻吩甲酸太阳能电池光敏染料,对染料的光、电化学性能进行测定.结果表明在模拟太阳光AM1.5照射下,以其为染料敏化剂的太阳能电池的光电转换效率达到0.12%.该染料具有良好的吸附性和光稳定性,适于用作太阳能电池的光敏染料.     

Electrolytes in solid-state dye-sensitized nanocrystalline solar cells

In this paper, the structure and operating principle of the dye-sensitized nanocrystalline solar cells (DSSC) are discussed. The electrolytes can be divided into three types: liquid electrolyte, quasi-solid electrolyte and solid electrolyte. Based on the relevant study of our group, we summarized mainly the research progress of the quasi-solid electrolyte and solid electrolyte in solid-state DSSC.     

Direct measurement of hole transport dynamics in DNA

Our understanding of oxidative damage to double helical DNA and the design of DNA-based devices for molecular electronics is crucially dependent upon elucidation of the mechanism and dynamics of electron and hole transport in DNA. Electrons and holes can migrate from the locus of formation to trap sites, and such migration can occur through either a single-step "superexchange" mechanism or a multistep charge transport "hopping" mechanism. The rates of single-step charge separation and charge recombination processes are found to decrease rapidly with increasing transfer distances, whereas multistep hole transport processes are only weakly distance dependent. However, the dynamics of hole transport has not yet been directly determined. Here we report spectroscopic measurements of photoinduced electron transfer in synthetic DNA that yield rate constants of approximately 5 x 10(7) s(-1) and 5 x 10(6) s(-1), respectively, for the forward and return hole transport from a single guanine base to a double guanine base step across a single adenine. These rates are faster than processes leading to strand cleavage, such as the reaction of guanine cation radical with water, thus permitting holes to migrate over long distances in DNA. However, they are too slow to compete with charge recombination in contact ion pairs, a process which protects DNA from photochemical damage.