柔性基底上有序生长六噻吩薄膜及其在太阳电池中的应用

【作者】 沐俊应；

【导师】 陈振兴；

【作者基本信息】 中南大学 ， 化学工艺， 2008， 硕士

【摘要】 有机半导体材料具有质量轻、柔韧易加工性、可低温大面积成膜等特点,将低成本的有机半导体材料用于微电子及光电子器件的研究近年来受到高度重视。六噻吩（6T）是迄今发现空穴迁移率最高的有机半导体材料之一,是有机薄膜晶体管半导体层、有机发光二极管空穴传输层、以及有机薄膜太阳电池电子给体层的潜在备选材料,相关薄膜沉积工艺及器件研究非常必要。采用石英晶体微天平实时监测薄膜生长速率,控制生长速率和基底温度,分别在柔性聚乙烯吡咯烷酮（PVP）绝缘层和柔性氧化铟锡（ITO）透明导电层上真空蒸发沉积了分子有序排列的六噻吩薄膜。X射线衍射（XRD）分析表明,生长速率太高或太低都将导致薄膜结晶度的下降。对PVP基底,六噻吩薄膜有序生长的条件为生长速率10nm/min、基底温度90℃,分子链取向始终与基底平行,降低基底温度将导致薄膜结晶度的下降。扫描电镜（SEM）分析显示,室温下沉积的六噻吩薄膜由10hm级宽、100nm级长的秆状晶粒构成,而较高温度下沉积的六噻吩薄膜则由1μm级尺寸的片状晶粒构成。后者结晶度明显高于前者,可见SEM与XRD分析结果一致。而对ITO基底,六噻吩薄膜有序生长的条件为生长速率10nm/min、基底温度50℃。基底温度显著影响六噻吩分子取向,室温下六噻吩分子链与基底呈一定夹角,随着温度的提高六噻吩分子链趋向与基底平行,且紫外可见光谱中514nm处吸收峰发生红移。在优化六噻吩薄膜沉积工艺的基础上,以ITO为基底制备了基于6T/C₆₀的柔性薄膜太阳电池。平面异质结器件ITO/6T/C₆₀/Al的C₆₀层恒定为60nm,将6T层厚度从20nm提高到40nm,发现30nm时器件光伏性能最佳,10m W·cm^-2模拟太阳光下短路电流Isc为0.380mA·cm^-2,开路电压Voc为0.330V,填充因子FF为0.41,光电转换效率η为0.51%。在C₆₀和Al层之间引入6nm厚度CuPc电极修饰层,FF及η均有所提高。采用单舟蒸发沉积了6T:C₆₀主体异质结薄膜,制备的混合型结构器件ITO/6T（20nm）/6T:C₆₀（20nm）/C₆₀（50nm）/Al的Isc为0.405mA·cm^-2,Voc为0.364V,FF为0.39,η为0.58%。更多还原

【Abstract】 Recently,great importance has been attached to the application of organic semiconductors in microelectronic and optoelectronic devices due to its potential low cost,low weight,flexibility,and easy processing. Sexithiophene（6T）is one of the organic semiconductors with the best holes transport mobility,thin film of which is promising candidate as semiconducting layer for organic thin film transistors,as holes transport layer for orgainc light emitting diodes,or as donor for organic thin film solar cells.Optimization of related film deposition processes and devices is critical.Through optimizing evaporation conditions such as substrate temperature and growth rate detected by in situ quartz crystal microbalance measurement,well-ordered sexithiophene films were deposited on both flexible insulating polyvinylpyrrolidone（PVP）layers and flexible transparent conductive indium tin oxide（ITO）layers.X-ray diffraction （XRD）investigations showed that too low or too high growth rate led to declined film crystallinity.On PVP substrate,well-ordered sexithiophene film was deposited at growth rate 10nm/min and substrate temperature 90℃.The main axis of sexithiophene molecules was found parallel to PVP substrate,and thin film crystallinity declined with the decrease of substrate temperature.Scanning electron microscope（SEM）investigations indicated that sexithiophene film deposited at room temperature was constituted of stalk grains with 10nm magnitude width and 100nm magnitude length, while sexithiophene film deposited at higher temperature was constituted of flake grains with size of 1μm magnitude.The latter was obviously crystalized better than the former,which was consistent with the XRD results.On ITO substrate,well-ordered sexithiophene film was deposited at growth rate 10nm/min and substrate temperature 50℃.Substrate temperature notably influenced molecule orientation of sexithiophene on ITO layers.At room temperature there existed an inclined angle between the main axis of sexithiophene molecules and ITO substrate surface.With the increase of substrate temperature,the main axis tended to parallel to substrate surface,and the UV/Vis absorption peak at 514nm occured redshift.Flexible thin film solar cells based on 6T/C₆₀heterojunction were vacuum deposited on ITO substrates based on the previously optimized preparation process of sexithiophene films.The thickness of 6T layers with the planar heterojunction devices ITO/6T/C₆₀/Al was varied from 20nm to 40nm without changing the 60nm thick C₆₀layer,and the optimum photovoltaic properties were obtained at 30nm with short circuit current （Isc）of 0.380 mA·cm^-2,open circuit voltage（Voc）of 0.330V,fill factor （FF）of 0.41,and photovoltaic conversion efficiency（η）of 0.51%. Introduction of a 6nm thick CuPc layer between C₆₀and Al layers resulted in higher FF andη.Single source evaporation was applied to deposit the bulk heterojunction thin film 6T:C₆₀,and the planar-mixed heterojunction device with structure of IYO/6T（20nm）/6T:C₆₀（20nm）/C₆₀（50nm）/Al performed Isc of 0.405 mA·cm^-2,Voc of 0.364V,FF of 0.39,andηof 0.58%.更多还原