【作者】 蒋方丹；

【导师】 冯嘉猷；

【作者基本信息】 清华大学 ， 材料科学与工程， 2007， 博士

【摘要】 进入21世纪以来,全球范围内能源和环境问题日益突出。太阳能具有取之不尽、用之不竭并且属于清洁能源等优点,成为解决能源短缺、环境污染和温室效应等问题的有效途径。薄膜太阳能电池兼具Si基太阳能电池高转换效率及成本较低的优点,其中,铜铟硒(CuInSe2, CIS)由于具有能够调整光学能隙、吸收率高(~6×105/cm)、抗辐射能力强和长期的稳定性等特点,被认为最有希望的薄膜太阳能电池材料之一。本文对CIS薄膜太阳能电池中有关薄膜材料的几个基础问题进行研究,研究内容主要包括实验和理论计算两个部分。实验部分研究了电沉积法和溅射Cu-In合金层硒化法制备CIS薄膜,并对这两种制备方法的关键工艺参数对CIS薄膜的性能影响进行了分析。研究了电沉积法的工作机理和工艺参数对CIS薄膜性能的控制规律,以及后续的真空退火处理对电沉积CIS薄膜的结晶性、表面形貌和薄膜成分的改善作用;研究了硒化温度对溅射Cu-In合金层硒化法制备CIS薄膜的工艺的影响,揭示了硒化过程中成分和物相的变化以及薄膜表面和截面形貌的变迁,提出了硒化过程中CIS薄膜生长的三个阶段;在反应溅射的MoNx薄膜基底上生长了强择优取向的CIS薄膜,并对择优取向的形成原因进行了分析。理论计算部分用第一性原理计算方法对CIS中的一些基础物理问题进行了研究。研究了CIS结构变形和同族元素取代对电子结构的影响,用化学键长的变化解释了能带结构的变化,并提示了CIS的结构参数和能隙随着同族元素取代量的变化规律;研究了CIS中的本征和非本征缺陷物理,对于黄铜矿相和CuAu结构的CIS,首次提出了有序缺陷化合物CuIn5Se8的两种稳定晶型,计算了CIS中本征和非本征缺陷的形成能随化学势和费米能级的变化规律,并对Na+掺杂所引入缺陷的作用机制进行了解释;对CIS与II-VI族化合物所形成的异质结的能带排列进行了计算,确定导带偏差ΔEc和价带偏差ΔEv对寻找CdS缓冲层的替代材料有重要指导意义。本文的研究结果对推进CIS薄膜太阳能电池的大规模应用具有积极的意义。更多还原

【Abstract】 Since the beginning of 21st century, global-scale energy and environmental issues have become increasingly prominent. Solar energy has the advantages of inexhaustible and clean energy, thus is effective solution to energy shortages, environmental pollution and the greenhouse effect. Thin film solar cells combine the high conversion efficiency as compared with Si based solar cells and the advantage of low cost. Meanwhile, copper indium diselenide (CuInSe2, CIS) is considered as the most promising materials for thin film solar cell application, owing to its ability to adjust optical band gap, high optical absorption coefficient (~6×105/cm), strong anti-radiation characteristics and long-term stability. In this thesis, we focus on some fundamental issues of CIS thin film materials for solar cell application, including the experimental and theoretical calculation parts.In the experimental part, the preparation of CIS thin film by electrodeposition and selenization of sputtered Cu-In alloy precursors is studied, and the effects of key process parameters on the properties of CIS thin films are analyzed. In the electrodeposition process, the work mechanism and the control of performance of CIS thin films by process parameter are studied. Also, the influence of follow-up vacuum annealing on the crystallization, surface morphology and composition profile of electrodeposited CIS thin films is investigated. Furthermore, the effect of selenization temperature on the properties of CIS thin films prepared by selenization of sputtered Cu-In alloy precursors is studied, revealing the selenium incorporation, phase change and evolution of surface and cross-section morphology of CIS thin films during selenization process. The three stage growth model of CIS thin films is also proposed. Moreover, it is revealed that CIS thin films deposited onto MoNx thin film substrate exhibit strong preferred orientation along (112) plane, and the enhancement of preferred orientation is attributed to the reduced lattice mismatch between MoNx and CIS with increasing N2 partial pressure during reactive sputtering of MoNx thin films.In the theoretical calculation part, we employ first principles calculation based on density functional theory (DFT) to study some basic physics problems in CIS. First, the electronic structure modification of CIS induced by structural deformation and composition alchemy is studied, in which the structural deformation is related to distortion of lattice constants (a and c) and anion displacementμand composition alchemy is related to substitution of components with the same group elements. The energy level movements induced by structural deformation are integrated by alteration of chemical bonds, and the changes of lattice parameter and band gap induced by composition alchemy are demonstrated. Also, the defect physics in CIS are studied by calculating the formation energy of intrinsic and extrinsic defects to evaluate the most favorite defect mechanism. Two stable polytypes of ordered defect compound CuIn5Se8 derived from chalcopyrite and CuAu type CIS are first reported in this thesis. Moreover, the roles of sodium induced extrinsic point defect and defect pairs in CIS are explained. Another topic is to determine the band alignment between CIS and II-VI group compounds (i.e. CdS, CdSe, ZnO, ZnS and ZnSe). The valence band offsetΔEv and conduction band offsetΔEc are calculated by means of average electrostatic potental.This thesis’s finds have positive significance to advance the large scale application of CIS thin film solar cells.更多还原