【作者】 王琰；

【导师】 侯延冰；

【作者基本信息】 北京交通大学 ， 光学， 2010， 博士

【摘要】 由于半导体纳米晶表现出特殊的光电性质,特别是硫族化合物纳米晶在光电子器件、生物、医学等领域有着广泛的应用。我们通过优化合成路线,制备高质量、单分散、形貌可控的半导体纳米晶,探索合成条件对纳米晶光学性质的可调性,使其可以在各个领域得到广泛的应用。本论文研究了水相和油相中硫族化合物纳米晶的合成与光学性质。利用常规的TEM、HRTEM、XRD、XPS、FTIR测试方法对所合成的材料进行表征,并研究不同的合成条件对产物光学性质的影响,探索材料的生长过程。1利用巯基乙酸为稳定剂在水相中合成出单分散的立方相CdTe纳米晶,粒径小于10nm。研究显示不同的反应条件制备的产物其光学性能也不同,随着反应时间、溶液PH值和Te/Cd比值的增加,CdTe发射峰会发生红移。在此基础上,我们研究了不同的体系,包括巯基丙酸(MPA), L-半胱氨酸(L-Cys),3-巯基-1,2-丙二醇(TG)作为稳定剂,并与巯基乙酸(TGA)体系相比较,研究了不同稳定剂对纳米晶的形貌、生长过程、稳定性以及光学性质的影响。实验结果表明,受稳定剂自身官能团性质和空间位阻的影响,用TGA、MPA、L-Cys、TG得到的CdTe纳米晶的吸收和发射峰位不同。用L-Cys做稳定剂时,纳米晶生长最快,产物粒径变大,从而得到最长的吸收波长和发射波长；用TG做稳定剂时,反应速度最慢,得到的纳米晶的吸收波长和发射波长最短。研究表明稳定剂中除了巯基对纳米晶表面有钝化作用外,稳定剂中的其它官能团也会控制纳米晶的生长从而影响纳米晶的尺寸和光学性质。稳定剂的性质也可以影响纳米晶的形貌和稳定性,用TGA合成的球状纳米晶比L-Cys包覆的纳米棒稳定性要好。2制备了合金型纳米晶ZnxCd1-xTe,并研究了不同制备条件对合金型纳米晶的光学性质的影响,及其在光伏器件中的应用。(?)在水相中合成出不同组分的ZnxCd1-xTe纳米晶,用XRD、TEM、HRTEM、XPS表征,并用Vegard定律证明了产物为合金结构。纳米晶分散性好,典型产物的粒径为5.6nm。(?)不同组分的合金纳米晶ZnxCd1-xTe随着Zn含量的增加,吸收光谱和发射光谱逐渐发生蓝移,合金纳米晶的禁带宽度随Zn/Cd比例的变化而改变。当Zn的浓度为30%时,纳米晶的发光量子效率达到最大。随着反应时间和反应温度的增加,合金纳米晶的粒径逐渐变大,吸收和发射光谱发生规律的红移现象,所有光谱都具备窄对称的良好发光性质。(?)将粒径小于10nm的ZnCdTe纳米晶掺到MEH-PPV：C60中,制备成器件结构为ITO/PEDOT:PSS/MEH-PPV：C60(+ZnCdTe)/Al的光伏器件。与纯的MEH-PPV器件和MEH-PPV:C60器件相比较,器件掺入合金纳米晶后,增强了器件的光电流响应。当ZnCdTe掺杂浓度不高于40%时,器件ITO/PEDOT-PSS/MEH-PPV:C60(+ZnCdTe)/Al的短路电流密度、开路电压和能量转换效率等都随着纳米晶浓度的增加而增加；当纳米晶含量高于70%时,电池各个性能参数急剧下降。器件性能在ZnCdTe的掺杂浓度为40%时达到最佳,此时与未掺杂的器件相比,短路电流密度增加三倍,电池的能量转换效率增加到二倍。3采用简单的“一锅法”成功的合成了单分散、高质量的Cu2S纳米球和纳米片。实验方法简单且可控性强,避免了传统方法中提前制备含铜有机前驱物的复杂性。令在高温和低温下,分别研究了纳米晶的生长过程。用XRD、FTIR及理论计算证明了反应早期中间产物硫醇铜盐的生成。早期阶段生成的硫醇铜盐逐渐分解促进Cu2S的成核和生长过程,随着反应温度的升高或者反应时间的延长,微小的Cu2S纳米球(3-6 nm)逐渐转变成纳米片。(?)改变合成条件例如反应温度、反应时间、表面活性剂的量、反应前驱物的浓度、多次注入反应物等可以调节Cu2S纳米片的半径、厚度和长径比。反应温度影响硫醇铜盐的分解速度和效率、反应单体的浓度、反应单体与纳米晶表面间的传质速率、纳米晶的成核速度和生长等进而影响最终产物的尺寸；TOPO和十二硫醇的双稳定剂作用,使得产物尺寸随着TOPO量的增加而增大；采用高浓度和低浓度的反应前驱物,都可得到单分散性产物,变化规律符合LaMer模型。210℃下多次注入反应物,有效的增大了Cu2S纳米片尺寸可调范围。实验中制备的Cu2S纳米片的带隙可以在1.36-1.53 eV调节,产物具备宽的吸收带,使此材料可能在光伏太阳能电池方面存在潜在的应用前景。4通过优化合成路线,改变稳定剂、反应溶剂、反应物种类、反应温度等条件可以得到多种形貌的六方纤维锌矿结构的CuInS2纳米晶。令用无机金属铜铟盐做反应物,注入硫源之前加入TOPO做稳定剂,TOPO的存在不利于得到CuInS2纳米晶；注入硫源之后加入TOPO做稳定剂,得到六方纤维锌矿的片状CuInS2纳米晶。不加入TOPO时,随着硫源的热注入温度从60℃升高到160℃,纳米晶形貌从三角形占主体的颗粒转变成大的纳米片,并且晶体结构由四方晶相转变成六方晶相。令用无机金属铜铟盐做反应物,油胺做稳定剂,十八碳烯做溶剂的条件下,可以得到片状六方纤维锌矿CuInS2纳米晶。随着反应温度的增加,纳米片平均尺寸变大。(?)用有机金属铜铟盐做反应物,油胺做稳定剂和反应溶剂,高温160℃下热注入硫源得到CuInS2纳米片；室温下混合硫源和反应有机金属盐,可以得到分散性好的CuInS2纳米颗粒。令用有机金属铜铟盐做反应物,十二硫醇做稳定剂和反应溶剂,逐渐升高反应温度,CuInS2纳米晶从蝌蚪状纳米晶-纳米线-纳米棒发生形貌的转变。我们可以控制反应温度,简单有效地控制一维CuInS2纳米晶的形貌。初步研究了CuInS2纳米晶的自组装形成机理,初始反应生成的纳米颗粒在不同的反应温度下组装成不同形貌的一维结构。得到的一维CuInS2纳米晶都为六方纤维锌矿结构,吸收光谱覆盖了从可见到红外光区,预示着这种方法合成的样品在光伏器件领域存在潜在的应用前景。更多还原

【Abstract】 In this dissertation, the work is mainly focused on the synthesis and optical properties of chalcogenides nanomaterial fabricated in aqueous and oil phase. The nanomaterials are characterized by the measurement of TEM、HRTE2M、XRD、XPS、FTIR. We also studied the effect of the experimental conditions on optical properties of nanomaterials and the growth mechanism.1 CdTe nanocrystals was synthesized in aqueous solution with thioglycolic acid (TGA) as stabilizer, and the size is less than 10nm. The optical properties of products can be influenced by the reaction conditions. The emission peak shifts to long wavelength with increase in reaction time、PH value and the ratio of Te/Cd. Basing on the investigation on TGA-stabilized system, L-cysteine hydrochloride(L-Cys), 3-mercaptopropionic(MPA) and 1-thioglycerol(TG) were chosen as the stabilizers to investigate the effect of the stabilizers on the morphology, growth, stability and optical properties. CdTe nanocrystals capped with different stabilizers exhibit distinct UV-Vis absorption spectra and PL spectra. It is due to the different functional groups and stereo-hindrance effect. UV-Vis absorption spectra and PL spectra from CdTe nanocrystals obtained using L-Cys as the stabilizer shift to the longest wavelengths. That using TG as the stabilizer displays the shortest wavelengths. Besides sulfhydryl group (-SR) of all stabilizers can combine with Cd2+to form complexes, the other substituents of the stabilizer also affect the size and optical properties of CdTe nanocrystals. Moreover, the stability and morphology can also been effected by the property of stabilizer. The TGA-stabilized nanospheres are more stable than L-Cys-stabilized nanorods.2 We successfully synthesized ZnxCd1-xTe alloyed nanocrystals in aqueous solution with TGA as the stabilizer, at lower temperature by using a facile route. We studied the effect of the reaction conditions on optical properties of alloyed nanocrystals and probed into their application in photovoltaic devices.(?)ZnxCd1-xTe alloyed nanocrystals with different compositions were synthesized in aqueous solution with thioglycolic acid (TGA) as stabilizer. The synthesized nanocrystals were characterized by XRD, TEM, HR-TEM and XPS. The structure of alloyed nanocrystals was confirmed by Vegard law. The ZnxCd1-xTe alloyed nanocrystals have a good dispersity with typical size of 5.6nm. (?)Composition-dependent absorption and PL spectra shift to short wavelength with increasing Zn content due to the change of band gap. The highest PL quantum yield (QY) of ZnxCd1-xTe alloyed nanocrystals is achieved when the concentration of Zn is 30%. The particle size increases with raised refluxing time and synthesis temperature, which led to the red shift of absorption and PL spectra. All the samples display a narrow symmetric-band and few electronic defect PL properties.(?) We blend the alloyed nanocrystals (<10nm) with the MEH-PPV:C6o to prepare photovoltaic devices. The structure of device is ITO/PEDOT:PSS/MEH-PPV:C6o(+ZnCdTe)/Al. Comparing the spectral response of photocurrent of the MEHPPV:C6o(+ZnCdTe) nanocomposite device with that of the devices based on MEH-PPV:C6o and pristine MEH-PPV, one can find that the nanocomposite device exhibits an enhanced photocurrent. When the weight ratio is not higher than 40%, the short current density, the open-circuit voltage and the power conversion efficiency increased with the weight ratio of ZnCdTe nanocrystals raised. The characteristics of the devices degraded when the concentration of ZnCdTe nanocrystals is too high up to 70%. The power conversion efficiency is doubled and the short current density is close to triple by blending ZnCdTe nanocrystals with the concentration of 40%.3 Mono dispersed copper(I) sulfide (Cu2S) nanodisks with high quality were synthesized by using a simple one-pot colloidal process, in which no pre-prepared organometallic precursors are required.(?) We studied the growth process of Cu2S nanocrystals at low and high temperature, respectively. Early product was characterized by XRD and FTIR and confirmed by theoretical arithmetic. Copper thiolate forms at the beginning of the reaction which effectively acts as a precursor whose decomposition leads to further nucleation and growth of Cu2S nanocrystals. That tiny naodots(3-6 nm) can gradually turn into nanodiks with the reaction temperature or time increased.(?) The diameter, thickness, aspect ratio, and optical property of the Cu2S nanodisks can be adjusted systematically by changing the reaction time, the amount of surfactants, the concentration of the precursors and the frequency of multiple injections. The temperature can affect the stability of the intermediate complexes, the amount of monomer species, the mass transfer rate of the monomers to the surface of nanocrystals and the rates of both nucleation and growth. The size of nanocrystal is therefore various at different reaction temperature. Both TOPO and dodecanethiol are surfactants that direct the anisotropic growth of Cu2S nanodisks. As the amount of TOPO is increased, the size of nanodisks raised accordingly. Increasing the concentration of the precursors leads to still monodisperse samples with smaller size, which is consistent with the classic LaMer model. The adjustable range of size can be widened efficiently by multiple injections. The band gap of as-synthesized Cu2S nanodisks can be tuned in the range of 1.36-1.53 eV. The nanodisks show a broad absorption band, making them potential candidates for applications in photovoltaic devices.4 Wurtzite CuInS2 nanocrystals with different morphologies were synthesized by optimize the conditions containing the stabilizer, solvent, reaction temperature and precursors.(?) Using the inorganic metal salts as the precursors, the addition of TOPO before the injection of dodecanethiol is unfavorable for the formation of CuInS2 nanocrystals. Wurtzite CuInS2 nanocrystals can be synthesized with the addition of TOPO after the injection of dodecanethiol. CuInS2 nanoparticles can turn into large nanodisks with the increased injected temperature of dodecanethiol from 60℃to 160℃without the addition of TOPO, while the structure of CuInS2 nanocrystals can be changed from tetragonal to hexagonal pattern.(?) Using inorganic metal salts as the precursors, wurtzite CuInS2 nanodisks can be synthesized with oleylamine as the stabilizer and ODE as the solvent. The size of nanodisk increases with the raised reaction temperature.(?) Using the organic metal salts as the precursors, CuInS2 nanodisks can be achieved by the injection of dodecanethiol at 160℃with oleylamine as the stabilizer and solvent. But CuInS2 nanoparticles are synthesized with good dispersity when dodecanethiol is mixed with organic metal salts at room temperature.(?) Using organic metal salts as the precursors, the morphologies of CuInS2 nanocrystals transform in the orders of tadpole-like structure, nanowires and nanorods as the increase of temperature with dodecanethiol as the stabilizer and solvent. We can effectively control the morphology by change the reaction temperature. We studied the "oriented attachment" machanism at different temperature. All one-dimensional CuInS2 nanocrystals are assigned to hexagonal wurtzite pattern. The absorption spectra can cover from visible to infrared region, which make the materials have potential applications on photovoltaic devices.更多还原