立方结构PbSe薄膜在六角硒化镉单晶(0001)表面的外延生长研究

采用分子束外延技术在六角铅锌矿结构CdSe单晶基片(0001)表面生长了立方结构PbSe薄膜,通过对所生长PbSe薄膜的X射线衍射(XRD)及透射电镜(TEM)分析,阐明了所生长立方PbSe薄膜与六角纤锌矿结构CdSe (0001)的外延关系,高分辨率TEM分析结果显示:CdSe基片与PbSe薄膜之间界面清晰,PbSe薄膜的晶体结构完整,其电子衍射谱的各级衍射斑点无明显畸变;XRD分析结果显示:所生长立方PbSe薄膜为(100)取向,PbSe薄膜与CdSe单晶的面内外延关系为PbSe[110]//CdSe[100],并呈现出三种不同面内取向晶粒镶嵌排列的微观结构,这表明:虽然六角铅锌矿结构CdSe (0001)面与立方PbSe(100)面具有不同的对称性,但仍能生长出高质量的PbSe薄膜,并为PbSe薄膜的应用奠定了可能。     

PbSe单晶薄膜的分子束外延及其表面微结构

用分子束外延技术在BaF2（111）衬底上生长了PbSe单晶薄膜,观测了表面形貌和微结构．结果表明,在高Se／PbSe束流比（≥0．4）条件下,PbSe按照二维层状模式生长,外延层中的应力通过位错滑移发生塑性形变而获得充分弛豫,获得的PbSe薄膜是具有单原子层平整度的表面台阶和螺旋结构;降低Se／PbSe束流比至0．2,首次在PbSe样品表面观察到规则的三角形纳米孔状结构;当Se／PbSe束流比为0时,PbSe薄膜表面出现三维岛状结构,应力只能得到部分弛豫．在BaF2（111）衬底上分子束外延生长PbSe单晶薄膜的最佳温度为450℃．     

Pb1-xSrxSe薄膜材料的微结构和光学特性

采用分子束外延的方法在BaF2衬底（111）上制备出了高质量的Pb1-xSrxSe（0≤X≤0．050）薄膜．X射线衍射结果表明，Pb1-xSrxSe薄膜为立方相NaCl型晶体结构，没有观察到SrSe相分离现象，薄膜的取向为平行于衬底（111）晶面．薄膜晶格常数随Sr含量的增加逐渐增大，Sr含量由Vegard公式得到．再用理论模拟Pb1-xSrxSe薄膜透射光谱的方法得到了相应的带隙．最后通过介电函数模型拟合得到了PbSe和Pb1-xSrxSe薄膜在光子能量位于基本带隙附近的折射率n和吸收系数a．     

PbSe纳米晶的制备及在太阳能电池中的应用

基于简单的溶剂注射工艺制备了PbSe纳米晶，利用平均粒径为5nm的PbSe米晶制备了P3HT／PbSeeh,P3HT／PbSe／PCBM两种结构的纳米晶聚合物太阳能电池，P3HT／PbSe电池的最高光电转换效率为O．19％，而基于三相体系P3HT／PbSe／PCBM池的光电转换效率为2．09％，说明PCBM对提高电池的光电转换效率具有重要的作用。     

碳化硼薄膜制备的研究进展

综述了碳化硼材料的主要性能和制备碳化硼薄膜的主要方法,讨论了包括磁控溅射、离子束沉积和化学气相沉积等制备方法的优点及重要工艺参数,并就各方法指出了提高薄膜性能的主要措施,指出制备出更均匀、致密的碳化硼薄膜,提高薄膜与基体间的结合力,降低薄膜应力仍是今后研究的重点.     

高温超导薄膜微细图形制备工艺的研究进展

高温超导薄膜具有良好的物理性能,其微细图形在微电子器件中有非常广泛的应用.概述了高温超导薄膜微细图形的制备工艺及研究进展,重点介绍了高温超导薄膜微细图形制备方法中的光刻法、改性工艺、耐熔微掩膜制备法和Sol-gel法与化学修饰法相结合的基本原理、工艺特点及最新研究进展.首次把Sol-gel法与化学修饰法相结合制备薄膜的微细图形的工艺用于高温超导薄膜微细图形的制备中.     

透明氧化物薄膜的制备及其发展趋势

对近几年透明氧化物薄膜的制备进行了综述,重点介绍了溶胶-凝胶法、电沉积法、水热电化学法和喷雾热解法等方法的制备特点、性能评价以及透明氧化物薄膜的应用领域,并对今后透明氧化物薄膜的制备发展趋势进行了预测.     

CIS太阳电池材料的研究进展

综述了国内外太阳电池及其材料的发展概况.目前应用的光电转换材料主要有硅材料和化合物半导体材料,介绍了用这几类材料制作的太阳电池的特点,重点介绍了其光电转换效率.在薄膜电池材料中重点综述了铜铟硒(CIS)基薄膜太阳电池的研究进展.由于制约太阳电池发展的关键问题是制备成本高和转换效率低,提出了采用化学法制备CIS基薄膜材料及其梯度带隙,该方法将开辟高性能CIS基吸收层薄膜材料及其器件制备的低成本新途径.     

光催化二氧化钛薄膜的制备工艺研究进展

评述了制备二氧化钛薄膜的液相法、气相法和电化学法3大类方法的优缺点,以及3大类方法所包含的溶胶-凝胶、微乳液、磁控溅射、物理气相沉积、化学气相沉积、阳极氧化和微弧氧化等方法制备二氧化钛薄膜的工艺步骤、特点及研究进展.文章最后指出,液相法由于自身存在的优点,仍将是今后二氧化钛薄膜制备和研究的重点;而光催化性能更好的掺杂二氧化钛,其研究重点是探讨掺杂方式、制备方法和优化配比等.     

溶胶-凝胶法制备ITO薄膜研究进展

概述了近年来国内外溶胶-凝胶法(Sol-Gel)制备ITO薄膜的研究状况,对Sol-Gel法制备ITO薄膜工艺做了简要介绍,重点讨论了Sol-Gel法制备ITO薄膜的溶胶体系,分析比较了有机醇盐、无机盐以及掺入ITO粉末方法体系的优缺点,最后讨论了甩膜法、提拉法及平铺法在Sol-Gel法制备ITO薄膜中镀膜的应用.指出Sol-Gel法是一种高效可行的制备ITO薄膜的方法,有着广阔的应用前景.     

Band gap engineering in PbSe thin films from near-infrared to visible region by photochemical deposition method

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32–1.40 eV for films deposited on soda lime glass substrates and 1.46–1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10^?7–513 × 10^?7 (Ω cm)^?1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate.     

Effect of Ascorbic Acid Additions on the Mechanism Underlying the Growth of Nanostructured PbSe Films via Hydrochemical Deposition

The effect of ascorbic acid additions on the growth mechanism of thin PbSe films produced by hydrochemical deposition has been studied by atomic force microscopy (AFM). A fractal analysis of AFM images of the lead selenide films has shown that their formation follows the “cluster–particle” aggregation mechanism. The fractal dimension assessed by the box-counting method is 2.26 at an average grain size of ~150 nm. From the transmission spectra of the films grown at deposition times from 20 to 120 min, we have evaluated their optical band gap, which has been shown to decrease from 0.595 to 0.53 eV with increasing deposition time. These values are attributable to the manifestation of quantum size effects in the grown PbSe films.     

Temperature variation of thermoelectric power of vacuum deposited PbSe thin films and its thickness dependence

PbSe thin films of thicknesses in the range 20 to about 170 nm have been prepared on glass substrates held at room temperature by thermal evaporation of the bulk alloy at a pressure of 5×10^–5 torr. The thermoelectric power of these films has been evaluated as a function of temperature in the range 300 to 500 K from the thermal e.m.f. data. It was found that the thermoelectric power of all the films initially increases with increasing temperature, then reaches a maximum, and, with a further increase in temperature, decreases rapidly and also changes sign. The possible reasons for this peculiar behaviour have been given. It is also found that there is no systematic variation of thermoelectric power with thickness of the films. This is probably due to completely specular scattering at the external and internal surfaces of PbSe thin films or to changes in stoichiometry of different films.     

Structural,optical and electrical properties of PbS and PbSe quantum dot thin films

PbS and PbSe were prepared by hot injection method. The powders were used for preparing the corresponding films by using thermal evaporation technique. The structural, optical and electrical properties of PbS and PbSe thin films were investigated. The structural properties of PbS and PbSe were investigated by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray techniques (EDX). PbS and PbSe films were found to have cubic rock salt structure. The particles size ranged from 1.32 to 2.26 nm for PbS and 1.28–2.48 nm for PbSe. EDX results showed that PbS films have rich sulphur content, while PbSe films have rich lead content. The optical constants (absorption coefficient and the refractive index) of the films were determined in the wavelength range 200–2500 nm. The optical energy band gap of PbS and PbSe films was determined as 3.25 and 2.20 eV, respectively. The refractive index, the optical dielectric constant and the ratio of charge carriers concentration to its effective mass were determined. The electrical resistivity, charge carriers concentration and carriers mobility of PbS at room temperature were determined as 0.55 Ω cm, 1.7 × 10¹⁶ cm^?3 and 656 cm² V^?1 s^?1, respectively, and for PbSe films they were determined as 0.4 Ω cm, 9 × 10¹⁵ cm^?3 and 1735 cm² V^?1 s^?1, respectively. These electrical parameters were investigated as a function of temperature.     

Multiple exciton generation in films of electronically coupled PbSe quantum dots

We study multiple exciton generation (MEG) in electronically coupled films of PbSe quantum dots (QDs) employing ultrafast time-resolved transient absorption spectroscopy. We demonstrate that the MEG efficiency in PbSe does not decrease when the QDs are treated with hydrazine, which has been shown to greatly enhance carrier transport in PbSe QD films by decreasing the interdot distance. The quantum yield is measured and compared to previously reported values for electronically isolated QDs suspended in organic solvents at approximately 4 and 4.5 times the effective band gap. A slightly modified analysis is applied to extract the MEG efficiency and the absorption cross section of each sample at the pump wavelength. We compare the absorption cross sections of our samples to that of bulk PbSe. We find that both the biexciton lifetime and the absorption cross section increase in films relative to isolated QDs in solution.     

Size- and temperature-dependent charge transport in PbSe nanocrystal thin films

We report the size- and temperature-dependence of electron transport in thin films of PbSe nanocrystals. Upon increasing temperature over the range 28-200 K, the electron transport underwent a transition in mechanism from Efros-Shklovskii-variable-range-hopping (ES-VRH) to nearest-neighbor-hopping (NNH). The transition occurred at higher temperatures for films with smaller particles. The electron localization length, estimated from the ES-VRH model, was comparable to the nanocrystal size and scaled systematically with nanocrystal diameter. The activation energy from the NNH regime was also size-dependent, which is attributed both to size-dependent Coulomb effects and the size-distribution of nanocrystals.     

Lead selenide nanowire growth by vapor-liquid-solid mechanism under mask during plasma processing

Data on the formation of lead selenide (PbSe) nanowires under a stencil mask during the processing of epitaxial PbSe films in high-density inductively coupled plasma (ICP) of low-pressure argon RF discharge are presented. The nanowires were studied by high-resolution scanning electron microscopy and energy-dispersive X-ray spectroscopy. A physical model is proposed that explains the local formation of PbSe nanowires in terms of their catalytic growth according to the vapor-liquid-solid mechanism.     

Determining the internal quantum efficiency of PbSe nanocrystal solar cells with the aid of an optical model

We determine the internal quantum efficiency (IQE) of the active layer of PbSe nanocrystal (NC) back-contact Schottky solar cells by combining external quantum efficiency (EQE) and total reflectance measurements with an optical model of the device stack. The model is parametrized with the complex index of refraction of each layer in the stack as calculated from ellipsometry data. Good agreement between the experimental and modeled reflectance spectra permits a quantitative estimate of the fraction of incident light absorbed by the NC films at each wavelength, thereby yielding well-constrained QE spectra for photons absorbed only by the NCs. Using a series of devices fabricated from 5.1+/-0.4 nm diameter PbSe NCs, we show that thin NC cells achieve an EQE and an active layer IQE as high as 60+/-5% and 80+/-7%, respectively, while the QE of devices with NC layers thicker than about 150 nm falls, particularly in the blue, because of progressively greater light absorption in the field-free region of the films and enhanced recombination overall. Our results demonstrate that interference effects must be taken into account in order to calculate accurate optical generation profiles and IQE spectra for these thin film solar cells. The mixed modeling/experimental approach described here is a rigorous and powerful way to determine if multiple exciton generation (MEG) photocurrent is collected by devices with EQE<100%. On the basis of the magnitudes and shapes of the IQE spectra, we conclude that the 1,2-ethanedithiol treated NC devices studied here do not produce appreciable MEG photocurrent.     

Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability

The chemical stabilities of hybrid perovskite materials demand further improvement toward long‐term and large‐scale photovoltaic applications. Herein, the enhanced chemical stability of CH₃NH₃PbI₃ is reported by doping the divalent anion Se^2? in the form of PbSe in precursor solutions to enhance the hydrogen‐bonding‐like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe‐doped CH₃NH₃PbI₃ films exhibited >140‐fold stability improvement over pristine CH₃NH₃PbI₃ films. As the PbSe‐doped CH₃NH₃PbI₃ films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI₃‐based cell. As a bonus, the incorporated Se^2? also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.     

Lead Selenide (PbSe) Colloidal Quantum Dot Solar Cells with >10% Efficiency

Low‐cost solution‐processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as attractive active absorbers in solar cells due to their high multiple‐exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air‐stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution‐phase ligand exchange approach, and finally absorber films are prepared using a one‐step spin‐coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40‐day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low‐cost and high‐performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.