All-solid-state dye-sensitized solar cells with high efficiency

Dye-sensitized solar cells based on titanium dioxide (TiO(2)) are promising low-cost alternatives to conventional solid-state photovoltaic devices based on materials such as Si, CdTe and CuIn(1-x)Ga(x)Se(2) (refs 1, 2). Despite offering relatively high conversion efficiencies for solar energy, typical dye-sensitized solar cells suffer from durability problems that result from their use of organic liquid electrolytes containing the iodide/tri-iodide redox couple, which causes serious problems such as electrode corrosion and electrolyte leakage. Replacements for iodine-based liquid electrolytes have been extensively studied, but the efficiencies of the resulting devices remain low. Here we show that the solution-processable p-type direct bandgap semiconductor CsSnI(3) can be used for hole conduction in lieu of a liquid electrolyte. The resulting solid-state dye-sensitized solar cells consist of CsSnI(2.95)F(0.05) doped with SnF(2), nanoporous TiO(2) and the dye N719, and show conversion efficiencies of up to 10.2 per cent (8.51 per cent with a mask). With a bandgap of 1.3 electronvolts, CsSnI(3) enhances visible light absorption on the red side of the spectrum to outperform the typical dye-sensitized solar cells in this spectral region.     

Coaxial silicon nanowires as solar cells and nanoelectronic power sources

Solar cells are attractive candidates for clean and renewable power; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend and dye-sensitized solar cells, to demonstrate carrier multiplication, and to enable low-temperature processing of photovoltaic devices. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.     

A single-photon detector in the far-infrared range

The far-infrared region (wavelengths in the range 10 microm-1 mm) is one of the richest areas of spectroscopic research, encompassing the rotational spectra of molecules and vibrational spectra of solids, liquids and gases. But studies in this spectral region are hampered by the absence of sensitive detectors--despite recent efforts to improve superconducting bolometers, attainable sensitivities are currently far below the level of single-photon detection. This is in marked contrast to the visible and near-infrared regions (wavelengths shorter than about 1.5 microm), in which single-photon counting is possible using photomultiplier tubes. Here we report the detection of single far-infrared photons in the wavelength range 175-210 microm (6.0-7.1 meV), using a single-electron transistor consisting of a semiconductor quantum dot in high magnetic field. We detect, with a time resolution of a millisecond, an incident flux of 0.1 photons per second on an effective detector area of 0.1 mm2--a sensitivity that exceeds previously reported values by a factor of more than 10(4). The sensitivity is a consequence of the unconventional detection mechanism, in which one absorbed photon leads to a current of 10(6)-10(12) electrons through the quantum dot. By contrast, mechanisms of conventional detectors or photon assisted tunnelling in single-electron transistors produce only a few electrons per incident photon.     

有机太阳能电池的研究进展

回顾了近五年有机太阳能电池在电池材料和器件性能方面的研究进展．在材料方面,合成具有低带隙的化合物,使之与太阳光谱有更好的匹配,以提高对太阳光的吸收范围;在器件方面,通过使用异质结和纳米结构,使之在增加光吸收的同时保证激子的分离与有效迁移．有机聚合物太阳能电池是有机太阳能电池的发展方向,设计并合成具有低带宽和低HOMO能级的D—A型聚合物是提高其理论光能转化效率的关键．通过改进与提高电池的制作技术,充分挖掘新材料的潜力,将获得较大光能转换效率的有机太阳能电池．     

活性层混合溶剂的选择对高分子太阳能电池性能的影响

高分子有机太阳能电池因为其简单的制作工艺和轻便稳定的特性而引起人们的广泛研究。控制活性层的形貌对于提高有机太阳能电池的光电性能有着至关重要的意义。使用两种不同的混合溶剂(氯仿/1,8-二碘代辛烷和氯苯/1,8-二碘代辛烷)来制备PTB7-Th:PC_(70)BM活性层。发现使用氯苯/1,8-二碘代辛烷能使活性层获得更好的相分离效果,从而有利于光的吸收和电荷的分离。相对于氯仿/1,8-二碘代辛烷,使用氯苯/1,8-二碘代辛烷的太阳能电池的光电转化效率从7.21%大幅提高到了8.86%。这主要来自短路电流密度(从15.1 mA/cm~(-2)提高至16.7 mA/cm~2)和填充因子(从61.2%提高至66.3%)的提高。结果表明使用氯苯/1,8-二碘代辛烷作为混合溶剂有利于制备高性能的基于PTB7-Th:PC_(70)BM的有机太阳能电池。     

A novel cancer therapy using a M?ssbauer-isotope compound

Cancer radiotherapy uses high doses of ionizing radiation (1-10(2) Gy; 10(2)-10(4) rad) because only a small fraction of the absorbed dose leads to lethal double-strand breaks in DNA. These breaks are more efficiently produced by Auger electrons (1-10 eV nm-1) generated in proximity to the DNA. The energy of these electrons (on average 21 electrons for the decay of 125I) is dissipated within 10-100 nm of the Auger event and produces multiple double-strand DNA breaks. A single Auger event can be lethal to a cell and is comparable to more than 10(5) photon absorption events in conventional radiotherapy. We now report that 57Fe(III).bleomycin, administered to malignant cells in vitro and in vivo and irradiated with resonant M?ssbauer gamma rays (14.4 keV), causes ablation of the malignant cells, presumably by Auger cascade, with extremely small radiation doses--about 10(-5) Gy. As a basis for comparison, about 5 Gy is necessary to achieve a similar effect with conventional radiotherapy.     

基于表面等离子体增强的聚合物太阳能电池研究

为有效地提高聚合物电池器件的光吸收和电荷收集, 进而提高整体器件效率, 采用氧化钼(MoO₃)/银纳米粒子(Ag NPs)/氧化钼作为复合阳极缓冲层, 制备了反型聚合物太阳能电池, 并研究了在缓冲层中加入金属纳米颗粒对器件性能的影响。实验结果表明, 在MoO₃缓冲层中加入1 nm的Ag时, 器件的短路电流密度和光电转换效率都得到了提高, 短路电流密度从9.54 mA/cm²增加到12.83 mA/cm², 效率从2.14%提高到3.23%。Ag纳米颗粒的表面等离子体共振作用, 有效地提高了器件的光吸收和电荷收集, 提高了整体器件效率。     

Efficient organic photovoltaic diodes based on doped pentacene

Recent work on solar cells based on interpenetrating polymer networks and solid-state dye-sensitized devices shows that efficient solar-energy conversion is possible using organic materials. Further, it has been demonstrated that the performance of photovoltaic devices based on small molecules can be effectively enhanced by doping the organic material with electron-accepting molecules. But as inorganic solar cells show much higher efficiencies, well above 15 per cent, the practical utility of organic-based cells will require their fabrication by lower-cost techniques, ideally on flexible substrates. Here we demonstrate efficiency enhancement by molecular doping in Schottky-type photovoltaic diodes based on pentacene--an organic semiconductor that has received much attention as a promising material for organic thin-film transistors, but relatively little attention for use in photovoltaic devices. The incorporation of the dopant improves the internal quantum efficiency by more than five orders of magnitude and yields an external energy conversion efficiency as high as 2.4 per cent for a standard solar spectrum. Thin-film devices based on doped pentacene therefore appear promising for the production of efficient 'plastic' solar cells.     

Ultrasensitive solution-cast quantum dot photodetectors

Solution-processed electronic and optoelectronic devices offer low cost, large device area, physical flexibility and convenient materials integration compared to conventional epitaxially grown, lattice-matched, crystalline semiconductor devices. Although the electronic or optoelectronic performance of these solution-processed devices is typically inferior to that of those fabricated by conventional routes, this can be tolerated for some applications in view of the other benefits. Here we report the fabrication of solution-processed infrared photodetectors that are superior in their normalized detectivity (D*, the figure of merit for detector sensitivity) to the best epitaxially grown devices operating at room temperature. We produced the devices in a single solution-processing step, overcoating a prefabricated planar electrode array with an unpatterned layer of PbS colloidal quantum dot nanocrystals. The devices showed large photoconductive gains with responsivities greater than 10(3) A W(-1). The best devices exhibited a normalized detectivity D* of 1.8 x 10(13) jones (1 jones = 1 cm Hz(1/2) W(-1)) at 1.3 microm at room temperature: today's highest performance infrared photodetectors are photovoltaic devices made from epitaxially grown InGaAs that exhibit peak D* in the 10(12) jones range at room temperature, whereas the previous record for D* from a photoconductive detector lies at 10(11) jones. The tailored selection of absorption onset energy through the quantum size effect, combined with deliberate engineering of the sequence of nanoparticle fusing and surface trap functionalization, underlie the superior performance achieved in this readily fabricated family of devices.     

Photoresponse and carrier transport of protocrystalline silicon multilayer films

Alternating multilayer films of hydrogen diluted hydrogenated protocrystalline silicon (pc-Si:H) were prepared using a plasma-enhanced chemical vapor deposition technique.The microstructure of the deposited films and photoresponse characteristics of their Schottky diode structures were investigated by Raman scattering spectroscopy,Fourier transform infrared spectroscopy and photocurrent spectra.Microstructure and optical absorption analyses suggest that the prepared films were pc-Si:H multilayer films with a two-phase structure of silicon nanocrystals (NCs) and its amorphous counterpart and the band gap of the films showed a decreasing trend with increasing crystalline fraction.Photocurrent measurement revealed that silicon NCs facilitate the spatial separation of photo-generated carriers,effectively reduce the non-radiative recombination rate,and induce a photoresponse peak value shift towards the short-wavelength side with increasing crystallinity.However,the carrier traps near the surface defects of silicon NCs and their spatial carrier confinement result in a significant reduction of the diode photoresponse in the longwavelength region.An enhancement of the photoresponse from 350 to 1000 nm was observed when applying an increased bias voltage in the diode,showing a favorable carrier transport and an effective collection of photo-generated carriers was achieved.Both the spatial separation of the restricted electron-hole pairs in silicon NCs and the de-trapping of the carriers at their interface defects are responsible for the red-shift in photoresponse spectra and enhancement of external quantum efficiency.The results provide fundamental data for the carrier transport control of high-efficiency pc-Si:H solar cells.     

Investigation of Organic Solar Cells Based on Donor-Accepter Heterojunction

The single-layer structure and heterojunction structure organic solar cells based on copper phthalocyanine(CuPc),3,4,9,10-Perylenetetracarboxylic dianhydride(PTCDA)and fullerene C60 were fabricated to study their photovoltaic(PV)properties.The PV performance of heterojunction structure solar cells was improved compared with the single layer structure cell.This is due to the introduction of donor-acceptor heterojunction that both expands the absorption range and offers efficient exciton dissociation site.In heterojunction structure solar cells,the PV performance of device with C60 as acceptor has highly improved because C60 has longer diffusion length of excitons.     

Investigation of Organic Solar Cells Based onDonor——A ccepter Heterojunction

The single-l ayer structure and heterojunction structure organic solar cells based on copper phthalocyanine (CuPc),3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) and fullerene C60 were fabricated to study their photovoltaic (PV) properties. The PV performance of heterojunction structure solar cells was improved compared with the single layer structure cell.This is due to the introduction of donor-acceptor heterojunction that both expands the absorption range and offers efficient excit on dissociation site.In heterojunction structure solar cells,the PV performance of device with C60 as acceptor has highly improved because C60 has longer diffusion length o f excitons.     

Sn/Sn_3O_(4-x) heterostructure rich in oxygen vacancies with enhanced visible light photocatalytic oxidation performance

Sn_3O_4, a common two-dimensional semiconductor photocatalyst, can absorb visible light.However, owing to its rapid recombination of photogenerated electron-hole pairs, its absorption is not sufficient for practical application.In this work, a Sn nanoparticle/Sn_3O_(4-x) nanosheet heterostructure was prepared by in situ reduction of Sn_3O_4 under a H_2 atmosphere.The Schottky junctions formed between Sn and Sn_3O_(4-x) can enhance the photogenerated carrier separation ability.During the hydrogenation process, a portion of the oxygen in the semiconductor can be extracted by hydrogen to form water, resulting in an increase in oxygen vacancies in the semiconductor.The heterostructure showed the ability to remove Rhodamine B.Cell cytocompatibility experiments proved that Sn/Sn_3O_(4-x) can significantly enhance cell compatibility and reduce harm to organisms.This work provides a new method for the fabrication of a Schottky junction composite photocatalyst rich in oxygen vacancies with enhanced photocatalytic performance.     

两类异质结构中光生电荷分离效率与光电性质

首先制备Cu4Bi4S9纳米带与石墨烯不同比例复合体系(CBS-graphene),其中石墨烯质量分数分别为:0.4%,0.8%,1.2%,1.6%,2.0%和2.4%.以α-Fe_2O_3为电子受主,CBS和CBS-graphene为电子施主,制备成α-Fe_2O_3/CBS、α-Fe_2O_3/CBS-graphene两类异质结构及体相异质结太阳能电池.XRD检测结果表明,异质结两组分都达到了良好的结晶状态;而且,两类复合体系都呈现出了复合结构的光吸收特性,但光吸收性质无明显差异.对于CBS-graphene,随着石墨烯含量逐步增加其光伏性质逐渐增强,当石墨烯质量分数为1.6%时达到最佳光伏响应强度,此后其光伏性质逐渐减弱.稳态和电场诱导表面光电压谱表明两类异质结都具有优越的光伏性质,但α-Fe_2O_3/CBS-graphene呈现出明显优于α-Fe_2O_3/CBS的光伏响应.基于石墨烯质量分数为1.6%,α-Fe_2O_3/CBS和α-Fe_2O_3/CBS-graphene两类体相异质结太阳能电池最高光电转换效率分别为3.1%和6.8%.从异质结厚度、能级匹配、石墨烯导电网络以及优越的电子传输特性几个方面,详细讨论了光生电荷分离的影响因素及光生电荷传输动力学.     

Boosting charge collection efficiency via large-area free-standing Ag/ZnO core-shell nanowire array electrodes

Hybrid nanostructures, comprising of a metal core and a semiconductor shell layer, show great potential for a new generation of low-cost solar cells due to their unique electronic and optical properties. However, experimental results have fallen far short of the ultra-high efficiency(i.e. beyond Shockley-Queisser limit) predicted by theoretical simulations. This limits the commercial application of these materials. Here, a non-transparent organic solar cell with an array of Ag/ZnO nanowires has been experimentally fabricated to increase the internal quantum efficiency(IQE) by a factor of 2.5 compared to a planar counterpart. This result indicates a significant enhancement of charge collection efficiency due to the ultrafast Ag nanowire channels. This hybrid nanostructure can also serve as a perfect back reflector for semi-transparent solar cells, which can result in enhanced light absorption by a factor of 1.8 compared to the reference samples. The enhanced charge collection and light absorption can make these Ag/ZnO nanostructures available for the application of modern optoelectronic devices.     

P3HT和Spiro-OMeTAD共混物作为光活性层的杂化太阳电池性能

为降低电荷复合率,提高杂化太阳电池的性能,将P3HT与Spiro-OMeTAD共混后的混合物作为光活性层和空穴传输层,旋涂在Sb_2S_3纳米粒子敏化的TiO_2纳米棒(TiO_2NR/Sb_2S_3)复合膜上,制备成杂化太阳电池。通过SEM、紫外可见吸收光谱、XRD、电化学阻抗图谱、稳态荧光光谱、J-V曲线等手段,对杂化太阳电池的微观结构、光电转换特性进行了表征和测试。结果表明:P3HT与Spiro-OMeTAD共混物比例为15 mg/1 mL时,得到结构为FTO/TiO_2NR/Sb_2S_3/P3HT:Spiro-OMeTAD/Ag杂化太阳电池的电荷负荷率低,电子生命长,能量转换效率达到了4.57%。所制备的杂化太阳电池性能优良,具有良好的应用前景。     

P层厚度对InGaN单结太阳电池的影响

采用基于第一性原理和太阳电池基本方程的wxAMPS软件,在理想情况下,模拟计算了单结In0.65 Ga0.35 N太阳电池的光电特性。计算结果表明：当p层厚度从130 nm逐渐增加到220 nm时,入射的光子吸收能量减少,从而产生的光生载流子数目减少,进而引起了开路电压、短路电流密度以及电池的转换效率均逐渐减小,但是填充因子却反而逐渐增大,为对单结In0.65 Ga0.35 N太阳电池的设计提供了理论的参考依据。     

Enhanced power conversion efficiency in bulk heterojunction polymer solar cells through dual-interface morphology modification

Efficient bulk heterojunction (BHJ) polymer solar cells with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transfer layer (HTL) were fabricated via controlling the spin coating speed of the HTL solution on a particular fluorinated tin oxide substrates of a high roughness. It shows that the functions of the photovoltaic devices increase with the increase of the HTL surface roughness. Then, an imprinting technique was employed to transfer a suitable pattern of nanostructure arrays to the surface of active layers. At the optimized spin coating speed, the photovoltaic devices exhibited a 28.4% increase in efficiency after this imprinting treatment compared with that of nonimprinted photovoltaic devices. It is mainly attributed to the achievement of high interface areas between active layers and electrodes, which not only increases optical absorption by scattering but also facilitates charge carrier collection.     

太阳能电池充电转换模块

为了提高太阳能电池能量利用率,改善光伏发电系统的工作性能,提出了一种新型太阳能电池充电的电路拓扑方案。该方案在太阳能电池和蓄电池之间增加充电传导模块,采用动态电压调节方式实现蓄电池的常规充电和倍压充电,解决了弱光照时太阳能电池能量流失问题。通过制做实验样机进行测试,结果表明,模块具有完善的充电控制特性和低压工作性能,静态工作电流小于20μA,传送效率高达98%,是一款高效实用的充电控制模块。     

Hybrid solar cells based on poly（3-hexylthiophene） and electrospun TiO2 nanofibers modified with CdS nanoparticles

Organic–inorganic hybrid solar cells based on poly(3-hexylthiophene) and electrospun TiO2 nano bers were fabricated by solution process.The ef ciency of the device was improved by modifying CdS nanoparticles on the surface of TiO2 by electrochemical method.The CdS layer can lead to the increase of both open circuit voltage and short circuit current of the device,which are attributed to enhanced exciton dissociation and light absorption and suppressed carrier recombination by CdS at the heterojunction.However,too thick CdS layer led to increased series resistance and decreased ef ciency of the device.Therefore,the optimum condition of the CdS deposition was obtained,which increased the power conversion ef ciency of the device for about 50%.Our results indicate that the surface modi cation on the inorganic semiconductor layer is an effect way to improve the performance of the hybrid solar cells.