【作者】 谢超；

【导师】 吴玉程； 罗林保；

【作者基本信息】 合肥工业大学 ， 材料物理与化学， 2014， 博士

【摘要】 石墨烯具有优异的光学及电学特性，在未来光电子器件透明电极领域有广阔的应用前景。硅纳米结构尤其是垂直排列的硅纳米阵列结构具有优异的陷光能力和电荷传输能力，在新一代高性能太阳能电池领域吸引了人们广泛的研究兴趣。制备稳定低成本高转换效率的石墨烯/硅光伏器件是当前的研究热点与前沿方向。本文主要对基于石墨烯与硅纳米结构的高性能光伏器件的构造与光电性能展开系统研究。通过制备高质量石墨烯与多种具有优异陷光能力的硅纳米（微米）阵列结构，对硅纳米（微米）阵列结构进行表面钝化、对石墨烯进行修饰掺杂、以及引入电子阻挡层等手段构筑了高性能石墨烯/硅光伏器件。此外，还构筑了基于硅纳米线阵列的异质结器件并对其光伏和光电响应特性进行了研究。主要的研究结果如下：1）采用化学气相沉积法（CVD）合成出高质量的石墨烯，利用HNO3、AuCl3等对石墨烯进行掺杂，结合对石墨烯层数的控制，实现其导电性和功函数的调控；利用CVD、金属辅助化学刻蚀法及反应离子刻蚀等方法成功制备硅纳米线和多种具有优异陷光能力的硅纳米（微米）阵列结构。采用甲基和Pt纳米颗粒修饰对硅表面进行钝化，有效的降低其表面载流子复合速率。2）制备了单层石墨烯/硅纳米线阵列光伏器件，研究了器件结构与器件性能的关系，采用石墨烯分散液填充硅纳米线间隙将器件能量转换效率提升至2.15%；构建了单层石墨烯纳米带/多根硅纳米线光伏器件，研究了纳米线掺杂浓度与器件光伏性能的关系，纳米线掺杂浓度最高时器件能量转换效率达1.47%。3）提出采用硅纳米孔阵列以增加石墨烯与硅的有效结区面积，系统的研究了硅表面钝化、石墨烯层数、HNO3掺杂时间等因素对器件光伏性能的影响。通过优化条件，实现能量转换效率分别达6.85%和7.65%的基于硅纳米线阵列和硅纳米孔阵列光伏器件。通过引入有机电子阻挡层，降低了硅端电子扩散至石墨烯端复合的几率，器件效率进一步提升至8.71%和10.30%。构筑了石墨烯/硅微米孔阵列光伏器件，研究了孔阵列深度与其陷光能力以及器件光伏性能之间的关系。利用具有持续掺杂效果的AuCl3对石墨烯进行掺杂，器件能量转换效率提升至10.40%，且具有优异的稳定性。4）构筑了碳量子点/硅纳米线阵列三维核/壳异质结光电器件，研究了该异质结的整流比、开启电压、理想因子和势垒高度等参数。系统地对碳量子点层数与器件光伏性能的关系进行了研究，最优器件的能量转换效率为9.10%。进一步发现该器件可作为自驱动的高灵敏快速光电探测器并对光电探测的关键参数进行了研究。5）构建了p型CdTe纳米带/n型硅纳米线阵列异质结光电器件，研究了该异质结的关键参数。由于两种材料较为匹配的能带关系以及纳米线阵列优异的陷光能力，该异质结能充分吸收可见及近红外光，器件能量转换效率为2.3%，远高于基于平面硅的器件。此外，该器件还可以作为稳定的自驱动光电探测器并具有快的响应速度。本文在基于石墨烯与硅纳米结构高性能光伏器件的构造与光电性能研究中的主要创新之处为：通过调控石墨烯的导电性与功函数、降低硅表面载流子复合速率、增加硅纳米（微米）结构陷光能力、增大石墨烯与硅有效结区面积以及降低硅端载流子扩散至石墨烯端复合几率等手段构筑了高性能石墨烯/硅光伏器件；利用硅纳米线阵列优异的陷光能力、异质结的能带匹配关系和三维核/壳结构独特的电荷传输特性构建了高性能硅纳米线阵列异质结光电器件。更多还原

【Abstract】 Graphene is an attractive candidate for the application as transparent electrode infuture optoelectronic devices due to its extraordinary optical and electrical properties.Silicon (Si) nanostructures, especially Si nanoarray structures, are of tremendousinterests in new-generation solar cell applications, because of their outstandinglight-trapping and excellent carrier transport abilities. Construction of high efficiencygraphene/Si solar cells with low cost and stable performance has attracted significantattention recently.In this thesis, we conducted a systematic study on the high-performance photovoltaicdevices based on graphene and Si nanostructures. The main investigations are focusedon the synthesis of high-quality graphene and various Si nano (micro) structures withexcellent light-trapping capability, modification and passivation of graphene and Si, aswell as construction of high-performance graphene/Si solar cells by using of electronblocking layer. Additionally, the heterojunction photovoltaic devices based on Sinanowire (SiNW) array were also fabricated and their photovoltaic and photoresponseproperties were studied. The main results are summarized as follows:1) High-quality graphene was synthesized by chemical vapor deposition (CVD)method, and HNO3and AuCl3doping were employed to tune its conductivity and workfunction. SiNWs and various Si nanoarrays (microarray) with excellent light-trappingabilities were prepared by using CVD, metal-assisted chemical etching and reactive ionetching methods. The carrier recombination activity at Si surface was effectivelysupressed by using a passivation method including CH3and Pt nanoparticlesmodification.2) We fabricated monolayer graphene/SiNW array Schottky junction solar cells andextensively studied the effect of device configuration on the photovoltaic characteristics.A maximum PCE of2.15%was achieved through filling the interspace of SiNW arraywith graphene suspension. Furthermore, solar cells based on monolayer graphenenanoribbon/multiple SiNWs were also constructed. By enhancing the doping level ofSiNWs, an optimal efficiency of1.47%was attained.3) We proposed a strategy to increase the effective junction area between grapheneand Si by using Si nanohole (SiNH) array. The effects of Si passivation, graphene layernumber, as well as HNO3doping time on the devices photovoltaic performance were studied. The PCEs of6.85%and7.65%were achieved for SiNW array/graphene andSiNH array/graphene devices, respectively, by optimizing the device architectures.What is more, the PCEs were substantially enhanced to8.71%and10.30%, respectively,through inserting an organic electron blocking layer between graphene and Si, whichcan lower the probability of electron diffusion from Si to graphene. Furthermore,photovoltaic devices based on graphene/Si micro-hole array were fabricated. The holesdepth and corresponding light-trapping ability were studied in order to increase thedevice photovoltaic performance. The maximum efficiency was enhanced to as high as10.40%with excellent air stability through doping graphene with AuCl3.4) Three-dimensional core-shell heterojunctions based on carbon quantum dots(CQDs) and SiNW array were first prepared, and some key parameters of theheterojunctions including rectification ratio, turn-on voltage, ideality factor as well asbarrier height were studied. The maximum PCE of9.10%was achieved by optimizingthe CQDs layer number. In addition, the heterojuncitons can function as self-poweredvisible light photodetectors with high-sensitivity and high-speed. Some key parametersrelated to photodetector were also investigated.5) We successfully fabricated p-CdTe nanoribbon/n-SiNW array heteojunctionoptoelectronic devices and investigated some key parameters of the heteojunction. Dueto their matched energy bandgap and outstanding light-trapping ability of SiNW array,the heterojunctions can effectively absorb most incident light ranging from visible tonear-infrared (NIR), giving rise to an PCE of2.3%, much higher than that of planar Sibased device. What is more, the heterojunctions can serve as high-speed self-poweredphotodetectors operated in the visible to NIR range with good stability.The main innovations of this thesis are:(1) The high-performance graphene/Si solarcells were achieved through tuning the conductivity and work function of graphene,reducing the surface carrier recombination velocity of Si, enhancing the light-trappingability of Si nano (micro) structures, increasing the effective junction area ofgraphene/Si as well as lowering the probability of electron diffusion from Si tographene.(2) The high-performance heteojunction optoelectronic devices based onSiNW array were attained by taking advantage of the excellent light-trapping ability ofSiNW array, the matched energy bandgap of heterojunction and the unique chargetransport property of three-dimensional core-shell structure.更多还原