半导体薄膜的制备及其光催化和光电性能研究

【作者】 吕伏建；

【导师】 李和兴；

【作者基本信息】 上海师范大学 ， 环境科学， 2014， 博士

【摘要】 随着能源枯竭和能源大量使用带来的环境问题日益严峻，寻找新型清洁能源已经成为全球热点问题，太阳能的利用代表着未来能源发展的主要途径。从1839年至今，光电转化研究已取得了一系列重要进展，不仅奠定了坚实的理论基础，而且在应用方面也取得了重大突破。光催化和染料敏化太阳能电池始于上世纪70年代和90年代，其基本原理是光子激发半导体禁带产生光生电子和空穴，从而产生氧化还原物种或光致电流。本论文着重研制新型可见光响应半导体薄膜材料、研究半导体薄膜材料形貌结构与光学吸收的内在联系、探究半导体薄膜材料光学吸收与光电转化效率的关系以及考察石墨烯对半导体薄膜电子转移效率的影响，具体研究内容分为以下四个方面：(1)采用TiF4乙醇溶液浸渍涂布在玻璃基底表面，由挥发诱导自组装制备介孔薄膜TiOF2可见光催化剂。通过浓度和温度调变对薄膜进行优化，结合能谱、红外、核磁等表征，探索薄膜形成机理。该薄膜具有较高结晶度，同时与玻璃基底具有化学键键合作用，从而导致良好的结合稳定度，在降解染料废水罗丹明B中显示高可见光催化活性和良好的使用寿命。薄膜同时也可以拓展到其它硅系的载体，并表现了良好的成膜性能和潜在应用功能。(2)采用钛片、四氟化钛和叔丁醇溶剂在160oC条件下发生溶剂热反应，制备出具有光增强吸收作用的TiO2光子晶体薄膜。通过调变反应时间、TiF4及HF酸含量，控制并优化光子晶体薄膜的生长，促进对光的选择性增强吸收。分别考察其在不同可控光区光源照射下，光催化降解染料废水中罗丹明B和亚甲基蓝的性能，发现光增强吸收作用显著提高光催化活性，结合相关表征，对其内在关系进行了探索。(3)采用乙醇、丙三醇和乙醚混合溶剂，以硫酸氧钛为钛源，控制反应时间来制备具有球型、核壳型和空壳型TiO2纳米球，并将之应用于染料敏化太阳能电池的散射层，考察了不同结构散射层对光的利用效率及光电转化效率的影响，发现空腔结构TiO2纳米球散射层能够显著提高光的利用率，结合多种表征手段，证明光的多次反射有利于提高了光的利用率，进而提高了光电转换效率。(4)将石墨作为双烯体，马来酸酣作为亲二烯体，采用微波辅助加热狄尔斯-阿尔德反应剥离石墨制备羧基功能化的石墨烯溶液，考察了温度与配体浓度对石墨烯结构的影响，确定最佳条件为温度180oC，石墨与马来酸酣的质量比为1：1.5。将石墨烯进行低温真空加热，发生狄尔斯-阿尔德反应逆反应，可以恢复石墨烯的导电性能，使石墨烯的薄膜方块电阻降低一个数量级，并利用功能化的石墨烯的羧基作为石墨烯与半导体薄膜TiO2的桥梁，提高染料敏化太阳能电池电子的传输速率，提高染料敏化太阳能电池的光电转化效率，结合多种表征手段，对石墨烯的形成机理以及光电转化构效关系进行了探索。更多还原

【Abstract】 Environment problem is becoming more and more serious, because of theexcess consumption of fossil energy and its decreasing resources. Consequently,finding new and clean energies has been a global issue. Solar energy is one of theimportant main routes to develop future sustainable energy. Since its first discoveryin1839, photoelectric conversion has achieved a series of important progressesincluding both fundamental theories and practical applications. Photocatalysis anddye-sensitized solar cells were proposed in the1970s and1990s, respectively. Theyfollow the same basic theory that photons excite the bandgap of semiconductor toproduce the photo-generated electrons (negative charge) and holes (positive charge),which then lead to redox species or photocurrent in the circuit.This thesis focuses on the following topics: synthesis of novel semiconductorfilms with visible light response, exploration of the relationship between themorphology of semiconductor films and its light absorbency, study on therelationship of light absorbency and photoelectric conversion, and investigation ofthe promoting effect on the electron mobility by adding functional graphene into thesemiconductor films. The main work can be divided into following4parts.(1) TiOF2mesoporous films were prepared by dipping-coating alcohol solutioncontaining TiF4onto a glass surface, followed by evaporation induced self-assemble.The formation mechanism was also revealed through characterizations of mapping,FT-IR, NMR and so on. Such TiOF2mesoporous films could be activated by visiblelights. Meanwhile, they also showed the high crystallization and binding strength dueto chemical bonding between TiOF2film and the SiO2substrate. As a result, theyshowed high activity and durability during photocatalytic degradation of RhodamineB in aqueous solution under visible light irradiation, which could be further optimizedby adjusting the TiF4concentration and reaction temperatures during preparation ofTiOF2films. These TiOF2films could also be coated onto other Si-base substrates bycovalently bonding, showing good potential in practical applications.(2) The TiO2photonic films were synthesized by solvothermal reaction of Ti foil, TiF4and tert-butyl alcohol at160oC. Such TiO2films showed enhanced lightabsorbance ability in certain wavelength. By optimizing reaction period, TiF4and/orHF amount, the TiO2films displayed strongly selective absorbance of lights withcharacteristic wavelengths. During photocatalytic degradation of rhodamine B andmethylene blue under visible lightirradiation, the TiO2films showed enhancedactivity at the irradiation of lights with characteristic wavelengths corresponding tothe strong light absorbance. The relationship between the selective light absorbanceand photocatalytic activity were investigated based on detailed characterizations.(3) TiO2microspheres with tunable chamber space (solid spheres, core shellspheres and hollow spheres) were synthesized by solvothermal reaction of mixedsolvents (alcohol, glycerin, diethyl ether) and TiOSO4at desired reaction periods.These microspheres were introduced into the dye sensitized solar cells (DSSCs) as ascattering layer encapsulated by two TiO2films comprised of uniform tiny TiO2nanoparticles, which exhibited the promoting effect on the light harvesting and cellefficiency owing to the multiple light-reflections in the microsphere chambers andthe internal light reflections within the TiO2films, together with the reduced electricresistance for the electron-transfer.(4) Carboxyl-functionalized graphene was synthesized by Diels-Alder reactionunder microwave irradiation in which the graphite played the role as diene and themaleic anhydride was used as dienophile. Based on the investigation of the influenceof either the reaction temperature or the maleic anhydride concentration on thegraphene growth, the optimum conditions were determined as the reactiontemperature of180oC and the graphite/maleic anhydride weight ratio of1/1.5. Whenthe as-received graphene were treated under vacuum at elevated temperatures, thereverse Diels-Alder reaction took place, leading to the recovery of the conductivity.The square resistance measurements showed the recovered graphene’s conductivitywas as10times as the functional graphene. Such carboxyl functional group played arole as a bridge between graphene and TiO2semiconductor films, leading to thegreat increase of electron mobility of the TiO2films, which could remarkablypromote photoelectric conversion efficiency. The formation mechanism of carboxyl functional graphene was examined based on detailed characterizations. Meanwhile,the correlation of photoelectric conversion efficiency to the graphene compositionand structure was also explored.更多还原