Hybrid polymer/zinc oxide photovoltaic devices with vertically oriented ZnO nanorods and an amphiphilic molecular interface layer

We report on the effect of nanoparticle morphology and interfacial modification on the performance of hybrid polymer/zinc oxide photovoltaic devices. We compare structures consisting of poly-3-hexylthiophene (P3HT) polymer in contact with three different types of ZnO layer: a flat ZnO backing layer alone; vertically aligned ZnO nanorods on a ZnO backing layer; and ZnO nanoparticles on a ZnO backing layer. We use scanning electron microscopy, steady state and transient absorption spectroscopies, and photovoltaic device measurements to study the morphology, charge separation, recombination behavior and device performance of the three types of structures. We find that charge recombination in the structures containing vertically aligned ZnO nanorods is remarkably slow, with a half-life of several milliseconds, over 2 orders of magnitude slower than that for randomly oriented ZnO nanoparticles. A photovoltaic device based on the nanorod structure that has been treated with an amphiphilic dye before deposition of the P3HT polymer yields a power conversion efficiency over four times greater than that for a similar device based on the nanoparticle structure. The best ZnO nanorod:P3HT device yields a short circuit current density of 2 mAcm(-2) under AM1.5 illumination (100 mW cm(-2)) and a peak external quantum efficiency over 14%, resulting in a power conversion efficiency of 0.20%.     

P3HT修饰一维有序壳核式CdS/ZnO纳米棒阵列复合膜的光电化学性能

采用电化学方法在铟锡氧化物(ITO)导电玻璃上制备了高度有序的ZnO纳米棒阵列, 在ZnO纳米棒阵列上先后电化学沉积CdS纳米晶膜及聚3-己基噻吩(P3HT)薄膜得到P3HT修饰的一维有序壳核式CdS/ZnO纳米阵列结构, 并通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、能量散射X射线(EDX)等表征手段证实了该结构的形成. 以此纳米结构薄膜为光阳极组装新型半导体敏化太阳电池, 研究了CdS纳米晶膜的厚度和P3HT薄膜的沉积对电池光伏性能的影响, 初步探讨了电荷在电池结构中的传输机理, 结果表明, CdS纳米晶膜和P3HT薄膜的沉积有效地拓宽了光阳极的光吸收范围, 实验中电池的光电转换效率最高达到1.08%.     

P3HT/CdS/TiO2/ZnO一维有序核壳式纳米棒阵列的构制及其在杂化太阳电池中的应用研究

采用恒电位法在铟锡氧化物导电玻璃(ITO)上制备了高度有序一维ZnO纳米棒阵列,将ZnO纳米棒阵列在TiO2溶胶中采用提拉法制备出了一维TiO2/ZnO核壳式纳米棒阵列.在一维TiO2/ZnO核壳式纳米棒阵列上电沉积CdS纳米晶得到一维CdS/TiO2/ZnO核壳式纳米棒阵列,然后在一维CdS/TiO2/ZnO核壳式纳米棒阵列上电沉积聚3-己基噻吩(P3HT)薄膜得到P3HT/CdS/TiO2/ZnO核壳式纳米结构薄膜.以该纳米结构薄膜电极为光阳极制备出新型纳米结构杂化太阳电池,研究了该类电池的光电转换性能,初步探讨了该类电池的工作机理.     

Improved performance of dye sensitized ZnO nanorod solar cells prepared using TiO2 seed layer

Zinc oxide (ZnO) nanorods of different structures have been grown on indium-doped tin oxide substrates by using TiO₂ as seed layer. The ZnO nanorods have been prepared using TiO₂ seed layers annealed at different temperatures via a simple sol–gel method. The X-ray diffraction result indicates that the prepared samples are of wurtzite structure. Dye sensitized solar cells have been fabricated using the prepared ZnO nanorods. The open circuit voltage, short circuit current density, fill factor, and power conversion efficiency of the ZnO nanorod based dye sensitized solar cells prepared using TiO₂ seed layers annealed at different temperatures have been determined. The improvement in power conversion efficiency may be due to the flower like structured ZnO nanorods with smaller diameter and large specific surface area which paves way for the efficient electron transfer in hybrid solar cells.     

Synthesis of ZnO nanorods and their application in quantum dot sensitized solar cells

ZnO nanorod thin films of different thicknesses and CdS quantum dots have been prepared by chemical method. X-ray diffraction pattern reveals that the CdS quantum dot and ZnO nanorods are of hexagonal structure. Field emission scanning electron microscope images show that the diameter of hexagonal shaped ZnO nanorods ranges from 110 to 200 nm and the length of the nanorod vary from 1.3 to 4.7 μm. CdS quantum dots with average size of 4 nm have been deposited onto ZnO nanorod surface using successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with ZnO nanorod has been used as photo-electrode in quantum dot sensitized solar cells. The efficiency of the fabricated CdS quantum dot-sensitized ZnO nanorod-based solar cell is 1.10 % and is the best efficiency reported so far for this type of solar cells.     

CdS量子点敏化ZnO纳米棒阵列电极的制备和光电化学性能

采用连续式离子层吸附与反应法制备了CdS量子点敏化的ZnO纳米棒电极.应用扫描电子显微镜(SEM)、X射线衍射(XRD)和透射电子显微镜(TEM)对CdS量子点/ZnO纳米棒电极的形貌、晶型和颗粒尺寸进行了分析和表征;采用光电流-电位曲线和光电流谱研究了不同CdS循环沉积次数及不同沉积浓度对复合电极的光电性能影响.结果表明,前驱体浓度都为0.1mol·L-1且沉积15次敏化后的ZnO纳米棒阵列电极光电性能最好.与单纯的ZnO纳米棒阵列电极和单纯的CdS量子点电极相比,其光电转换效率显著提高,单色光光子-电流转换效率(IPCE)在380nm处达到76%.这是因为CdS量子点可以拓宽光的吸收到可见光区,并且在所形成的界面上光生载流子更容易分离.荧光光谱实验进一步说明了光电增强的原因是,两者间形成的界面中表面态大大减少,有利于减少光生电子和空穴的复合.     

Electrical investigation and ultraviolet detection of ZnO nanorods encapsulated with ZnO and Fe-doped ZnO layer

Encapsulated ZnO nanorod arrays were fabricated using a two-step method; hydrothermal followed by dip-coating. Intensity of X-ray diffraction peaks of ZnO nanorod films increased by encapsulation with ZnO and Fe doped ZnO layer. Encapsulation process increased diameter of the rods in a range of 20–40 nm. The optical studies indicated that the band-gap decreased with increment of the nanorod diameter, and increased with Fe doping in the ZnO layer. The electrical resistance of the samples demonstrated a remarkable reduction due to encapsulation, especially in the sample encapsulated with Fe doped-ZnO layer. The photoresponse behavior of ZnO nanorod films was investigated under different powers of ultraviolet illumination. The photoresponsivity was improved for encapsulated nanorods as compared to bare nanorods.     

Comparison of two types of vertically aligned ZnO NRs for highly efficient polymer solar cells

Vertically aligned ZnO nanorods (NR) are prepared by two different syntheses methods and applied on polymer solar cells (PSCs). The ZnO electrodes work as the electron transport layer with the P3HT:PCBM blend acting as the active material. Several organic blend solution conditions are optimized: concentration, solvent, and deposition speed. The effect of different NR electrode morphologies is analyzed on the solar cell performance and characterized by current–voltage curves and IPCE analyses. The photovoltaic performance of the solar cells was observed to be influenced by many factors, among them infiltration of the organic P3HT:PCBM blend within the ZnO NR layer. The infiltration of the active layer was monitored by cross section SEM and energy dispersive X-ray spectroscopy analyses. Our results show that higher power conversion efficiencies are achieved when shorter NRs lengths are applied. The best power conversion efficiency obtained was 2.0% for a 400 nm ZnO NR electrode. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

籽晶层制备方式对氧化锌纳米棒阵列的影响

采用3种不同的方式制备ZnO薄膜籽晶层:旋涂、喷雾热解和脉冲激光沉积。对于每一种制备方式,其薄膜的晶体结构、形貌、表面粗糙度等性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行了表征。之后,通过水热合成方法,在3种籽晶层衬底上制备得到具有不同结构和形貌特征的ZnO纳米棒阵列。结果表明,ZnO纳米棒生长和籽晶层制备方式具有极强的相关性。最后,对两者相关性的生长机理进行了解释。     

Fabrication and evaluation of ZnO nanorods by liquid-phase deposition

The ZnO nanorod growth mechanism during liquid-phase deposition (LPD) has been investigated, with results considered in the context of phase stabilization, LPD chemical processes, and Gibbs free energy and entropy. Zinc oxide (ZnO) possesses unique optical and electronic properties, and obtaining ZnO species with high specific surface area is important in ZnO applications. Highly c-axis-oriented ZnO films are expected to be utilized in future optical and electrical devices. ZnO nanorods were synthesized using an aqueous solution deposition technique on a glass substrate with a free-standing ZnO nanoparticle layer. ZnO nanorod growth was easily controlled on the nanoscale by adjustment of the immersion time (15-210 min). X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), and film thickness measurements were used to characterize the crystalline phase, orientation, morphology, microstructure, and growth mechanism of the ZnO nanorods. FE-SEM images were analyzed by image processing software, which revealed details of the of ZnO nanorod growth mechanism.     

Photoelectrochemical performance of a sub-micron structured film with poly(3-methylthiophene) (P3MT)-modified CdTe/ZnO shell-core sub-micron tube arrays

A sub-micron structured film with a poly(3-methylthiophene) (P3MT)-modified CdTe/ZnO shell-core sub-micron tube array has been prepared by a series of electrodeposition processes, and a semiconductor-sensitized solar cell based on this structure was also fabricated. Vertically oriented ZnO sub-micron tubes were obtained on an indium tin oxide (ITO) substrate, and then CdTe nanocrystals and a thin P3MT layer were electrodeposited sequentially onto the walls of the ZnO sub-micron tubes. A suitable thickness of CdTe and P3MT could improve the photovoltaic properties of the solar cell, which was attributed to the enhancement in the light absorption and the decrease in the recombination of photogenerated carriers. In addition, a p-n heterojunction formed between the interface of CdTe and P3MT played an important part in the efficient separation and fast transport of photogenerated carriers in the sub-micron structure. A power conversion efficiency of 1.20% was obtained with this type of solar cell.     

Tuning the Dimensions of ZnO Nanorod Arrays for Application in Hybrid Photovoltaics

ZnO nanorod arrays are a very eligible option as electron acceptor material in hybrid solar cells, owing to their favorable electrical properties and abundance of available, easy, and low‐cost synthesis methods. To become truly effective in this field, a major prerequisite is the ability to tune the nanorod dimensions towards optimal compatibility with electron‐donating absorber materials. In this work, a water‐based seeding and growth procedure is used to synthesize ZnO nanorods. The nanorod diameter is tuned either by modifying the zinc concentration of the seeding solution or by changing the concentration of the hydrothermal growth solution. The consequences of this morphological tailoring in the performance of hybrid solar cells are investigated, which leads to a new record efficiency of 0.82 % for hydrothermally grown ZnO nanorods of size 300 nm in combination with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). This improvement is attributed to a combined effect of nanorod diameter and orientation, and possibly to a better alignment of the P3HT backbone resulting in improved charge transport.     

Effects of substrates and seed layers on solution growing ZnO nanorods

Oriented ZnO nanorods were fabricated in a two-step approach, including the synthesis of seed layer on different substrates and the growth of ZnO nanorods in aqueous solutions of zinc nitrate and hexamethylenetetramine at low temperature. The effects of seed layer synthesized by different methods, sol–gel method and electrochemical deposition method, on the orientation and morphologies of ZnO nanorods were compared in detail. The optimal parameters for the growth of highly oriented ZnO nanorod arrays were found and the forming mechanism was also disclosed. Furthermore, as an application of the ZnO nanorod film, dye-sensitized solar cells based on it were successfully fabricated. The cell performances of ZnO nanorods grown on ED-ZnO seed layer deposited at −700 mV were higher than those with SG-ZnO seed layer due to good nanostructure.     

Sb2S3纳米粒子修饰ZnO纳米片微纳分级结构的光电化学性能

采用恒电位方法,选择氯化钾和乙二胺(EDA)为添加剂,在氧化铟锡(ITO)导电玻璃上制备了高度有序的ZnO纳米片阵列,通过二次电沉积得到了ZnO纳米片上生长纳米棒的微纳分级结构.利用化学浴沉积法在ZnO基底上沉积Sb₂S₃纳米粒子制备出了Sb₂S₃/ZnO纳米片壳核结构和Sb₂S₃/ZnO微纳分级壳核结构.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、紫外-可见(UV-Vis)吸收光谱、瞬态光电流等对其形貌、结构组成和光电化学性能进行了表征和分析.结果表明, Sb₂S₃/ZnO纳米片上生长纳米棒分级壳核结构的光电流明显高于Sb₂S₃/ZnO纳米片壳核结构.在Sb₂S₃/ZnO纳米片壳核结构和Sb₂S₃/ZnO微纳分级壳核结构的基础上旋涂一层P3HT薄膜形成P3HT/Sb₂S₃/ZnO复合结构,以上述复合结构薄膜为光活性层组装成杂化太阳电池,其中, P3HT/Sb₂S₃/ZnO分级壳核结构杂化太阳电池的能量转换效率最高,达到了0.81%.     

The effect of hydrothermal growth temperature on preparation and photoelectrochemical performance of ZnO nanorod array films

Highly oriented ZnO nanorod arrays with controlled diameter and length, narrow size distribution and high orientation consistency have been successfully prepared on ITO substrates at different growth temperatures by using a simple hydrothermal method. XRD results indicate that the nanorods are high-quality single crystals growing along [001] direction with a high consistent orientation perpendicular to the substrate. SEM images show that the nanorods have average diameters of about 30-70 nm by changing growth temperature. The thin films consisting of ZnO nanorods with controlled orientation onto ITO substrates allow a more efficient transport and collection of photogenerated electrons through a designed path. For a sandwich-type cell, the relatively high overall solar energy conversion efficiency reaches about 2.4% when the growth temperature is at 95 °C.     

基底对电沉积制备ZnO纳米棒阵列的影响

采用恒电位电沉积方法, 在未经修饰的ITO导电玻璃基底上通过控制实验条件制备出不同形貌的纳米ZnO结构, 而在经过ZnO纳米粒子膜修饰后的ITO导电玻璃基底上, 制备出透明、高取向、粒径小于30 nm的ZnO纳米棒阵列. 用扫描电子显微镜(SEM)、X射线衍射(XRD)以及透射光谱对制备出的ZnO纳米棒阵列的结构、形貌和透明性进行了表征. 测试结果表明, ZnO纳米棒阵列的平均直径为21 nm, 粒径分布窄, 约18～25 nm, 择优生长取向为[001]方向, 垂直于基底生长. 当入射光波长大于400 nm时, ZnO纳米棒阵列的透光率大于95%.     

Magnesium doped ZnO nanoparticles embedded ZnO nanorod hybrid electrodes for dye sensitized solar cells

We report a novel type of Mg doped ZnO nanoparticles (ZMP) embedded on hydrothermally grown ZnO nanorod (ZR) based photoanode dye sensitized solar cells. The crystallinity, composition and morphology of the photoanodes were characterized by using X-ray diffraction analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The amount of dye absorbed in the photoanode was observed using UV visible spectral analysis. The improved internal resistance and charge-transfer kinetics of the fabricated cells were analyzed using electrochemical impedance spectroscopy. The ZMP embedded electrode of low thickness (~2.5 μm) gained an enhanced short-circuit current density of 8.56 mA/cm², open-circuit photo voltage of 0.71 V, fill factor of 0.51, and overall conversion efficiency of 2.91 % under 1 sun illumination. This shows high conversion efficiency and performance than that of ZnO nanorod (η ~ 0.22 %) and bare ZnO nanoparticles (ZP) embedded ZnO nanorod (η ~ 1.04 %) based cells. The presence of Mg ions in the ZnO nanoparticle hinders the interfacial recombination of the photo-excited electrons with the electrolyte and also shows better dye absorption than that of ZR. These factors can significantly enhance solar-cell performance and increase the efficiency of the ZMP based dye sensitized solar cells.     

Controlled growth of well-aligned ZnO nanorod array using a novel solution method

A simple method of synthesizing nanomaterials and the ability to control the size and position of them are crucial for fabricating nanodevices. In this work, we developed a novel ammonia aqueous solution method for growing well-aligned ZnO nanorod arrays on a silicon substrate. For ZnO nanorod growth, a thin zinc metal seed layer was deposited on a silicon substrate by thermal evaporation. Uniform ZnO nanorods were grown on the zinc-coated silicon substrate in aqueous solution containing zinc nitrate and ammonia water. The growth temperature was as low as 60-90 degrees C and a 4-in. wafer size scale up was possible. The morphology of a zinc metal seed layer, pH, growth temperature, and concentration of zinc salt in aqueous solution were important parameters to determine growth characteristics such as average diameters and lengths of ZnO nanorods. We could demonstrate the discrete controlled growth of ZnO nanorods using sequential, tailored growth steps. By combining our novel solution method and general photolithography, we selectively grew ZnO nanorod arrays on a patterned silicon substrate. Our concepts on controlled ZnO nanorod growth using a simple solution method would be applicable for various nanodevice fabrications.     

Growth and Characterization of [001] ZnO Nanorod Array on ITO Substrate with Electric Field Assisted Nucleation

This paper reports direct growth of [001] ZnO nanorod arrays on ITO substrate from aqueous solution with electric field assisted nucleation, followed with thermal annealing. X-ray diffraction analyses revealed that nanorods have wurtzite crystal structure. The diameter of ZnO nanorods was 60–300 nm and the length was up to 2.5 μm depending on the growth condition. Photoluminescence spectra showed a broad emission band spreading from 500 to 870 nm, which suggests that ZnO nanorods have a high density of oxygen interstitials. Low and nonlinear electrical conductivity of ZnO nanorod array was observed, which was ascribed to non-ohmic contact between top electrode and ZnO nanorods and the low concentration of oxygen vacancies.     

CdS nanocrystallites sensitized ZnO nanorods with plasmon enhanced photoelectrochemical performance

A sandwiched structure of CdS/Ag/ZnO nanorod photoanode exhibits greatly enhanced photoelectrochemical activity for solar hydrogen generation, due to synergistic effect of CdS nanocrystallites and plasmonic Ag nanoparticles for the enhanced optical absorption and the promoted charge carrier separation.