天然染料敏化太阳能电池的性能研究

用水溶液榨取和无水乙醇萃取的方法分别从火龙果皮、心里美、紫甘蓝、冬青叶、麦冬果实、山竹皮、樟树叶和樟树果实8种天然植物中提取染料,测试了它们的紫外-可见光(UV-vis)吸收光谱.采用水热法制备了TiO2薄膜电极,利用X射线衍射(XRD)和扫描电子显微镜(SEM)对其物相和表面形貌进行了表征.制备了8种天然染料敏化的太阳能电池(DSSCs),测试了电池的光电性能和电化学阻抗谱(EIS).     

Fabrication of mixed perovskite organic cation thin films via controllable cation exchange

Here in this paper, we demonstrate a facile technique for creating the mixed formamidinium(HN = CHNH_3~+, FA~+)and methylammonium(CH_3NH_3~+, MA~+) cations in the lead iodide perovskite. This technique entails a facile drop-casting of formamidinium iodide(FAI) solutions on as-prepared MAPbI_3 perovskite thin films under the controlled conditions,which leads to controllable displacement of the MA~+ cations by FA~+ cations in the perovskite structure at room temperature. Uniform and controllable mixed organic cation perovskite thin films without a "bi-layered" or graded structure are achieved. By applying this approach to photovoltaic devices, we are able to improve the performances of devices through extending their optical-absorption onset further into the infrared region to enhance solar-light harvesting. Additionally,this work provides a simple and efficient technique to tune the structural, electrical, and optoelectronic properties of the light-harvesting materials for high-performance perovskite solar cells.     

δ-MnO2改性石墨烯气凝胶的制备及电化学性能

通过对还原石墨烯气凝胶(RGOA)进行δ-MnO_2纳米颗粒改性制备出锂离子电池负极,并获得了良好的电化学性能。同时研究了δ-MnO_2的负载量对三维复合RGOA/δ-MnO_2负极材料电化学性能的影响,发现随着δ-MnO_2负载量的增加,锂离子电池性能先增后减,在δ-MnO_2负载量合适时(160 mg)比容量达到最大值(1 701.9 mAh·g~(-1)),该值明显高于δ-MnO_2负极的理论容量1 230 m Ah·g~(-1)。此外,该RGOA/δ-MnO_2-160 mg负极即便在5 A·g~(-1)的大电流下经历600次循环后仍能保持210.5 mAh·g~(-1)的比容量。如此优异的电化学性能归因于RGOA的大比表面积和高导电性,以及δ-MnO_2颗粒的高比容量和高催化活性。此外,三维石墨烯气凝胶中大量的孔洞有利于提供足够的空间负载超细δ-MnO_2颗粒,避免了δ-MnO_2在嵌锂过程中的体积膨胀以及抑制了固液界面保护膜(SEM)的加厚。通过计算赝电容对锂离子电池比容量的贡献,证实RGOA/δ-MnO_2电极的充放电过程为赝电容行为所主导,这也是取得良好比容量和循环性能的另一重要原因。     

氟置换高岭石层间羟基的能量最小化模拟

为了进一步澄清高岭石中结构无序的成因以及氢键对它们的影响程度,利用补充了氟参数的CLAYFF力场,对层间羟基不同分数的氟置换进行了能量最小化模拟.结果发现:四面体底氧起皱的原因是四、八片层不匹配引起的Al—O(连接氧)键拉伸以及维持四面体自身外形的需要;四面体旋转的原因与Newnham的解释类似.八面体上下三原子对旋转是由于:(1)四、八面体层的不匹配,具体地说是连接氧/内部羟基氧与八面体铝之间的O—Al—O键角(θ1)和Al—O—Al键角(θ2),层间羟基氧与八面体铝之间的O—Al—O键角(θ4)和Al—O—Al键角(θ5)的增大,以及八面体共棱O—Al—O键角(θ3)的减小;(2)铝硅斥力引起的θ1、θ2变小和θ3变大;(3)(1)和(2)中所有键角变化引起的结构调整;(4)高岭石特殊的网状结构共同引起的.八面体O-O共享棱的缩短和铝更靠近层间羟基氧同样也是(1)-(4)作用的结果;θ1、θ2、θ4和θ5增大和θ3减小还引起了八面体展平.层间氢键对四面体底氧起皱、八面体展平和八面体上下三原子对旋转起阻碍作用,而对四面体旋转起促进作用.此外,当氟对层间羟基的置换摩尔分数较低时(xF=0-0.7),高岭石层间距并不明显随氟的增加而增加,这说明了高岭石的水合过程可能并不需要氟化铵的加入.     

SiO2干凝胶中CdS量子点的光致发光性质

以正硅酸乙酯(TEOS)为SiO2的前驱物,硝酸镉为镉源,硫脲为硫源,用溶胶-凝胶法制备了CdS量子点掺杂的SiO2干凝胶,利用XRD、紫外-可见吸收光谱、光致发光谱对其性质进行研究.样品的测试结果表明在SiO2干凝胶的网状结构中形成了CdS量子点,平均粒径为5.1 nm.SiO2凝胶中CdS吸收峰位置明显蓝移.在一定...     

Synthesis and application of TiO_2 single-crystal nanorod arrays grown by multicycle hydrothermal for dye-sensitized solar cells

TiO2 is a wide band gap semiconductor with important applications in photovoltaic cells. Vertically aligned Tit2 nanorod arrays （NRs） are grown on the fluorine-doped tin oxide （FTO） substrates by a multicycle hydrothermal synthesis process. The samples are characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, high-resolution transmission electron microscopy （HRTEM）, and selected-area electron diffraction （SAED）. It is found that dye-sensitized solar cells （DSSCs） assembled by the as-prepared Tit2 single-crystal NRs exhibit different trends under the condition of different nucleation and growth concentrations. Optimum cell performance is obtained with high nucleation concentration and low growth cycle concentration. The efficiency enhancement is mainly attributed to the improved specific surface area of the nanorod.     

Charge transfer modification of inverted planar perovskite solar cells by NiOx/Sr:NiOx bilayer hole transport layer

Perovskite solar cells (PSCs) are the most promising commercial photoelectric conversion technology in the future. The planar p-i-n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability. However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-level-matched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO$_{x}$/Sr:NiO$_{x}$ bilayer hole transport layer (HTL) improves the holes transmission of NiO$_{x}$ based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves $J_{\rm sc}$. As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 mA$\cdot$cm$^{-2}$ and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.     

石墨烯/尖晶石LiMn2O4纳米复合材料制备及电化学性能

采用溶胶凝胶法和还原氧化石墨法制备尖晶石LiMn2O4纳米晶和石墨烯纳米片,并采用冷冻干燥法制备了石墨烯/尖晶石LiMn2O4纳米复合材料,利用XRD、SEM、AFM等对其结构及表面形貌进行表征;利用CV、充放电、EIS研究纳米复合材料的电化学性能和电极过程动力学特征。结果表明:纳米LiMn2O4电极材料及其石墨烯掺杂纳米复合材料的放电比容量分别为107.16 mAh.g-1,124.30 mAh.g-1,循环100周后,对应容量保持率为74.31%和96.66%,石墨烯可显著改善尖晶石LiMn2O4电极材料的电化学性能,归结于其良好的导电性。纳米复合材料EIS上感抗的产生与半导体尖晶石LiMn2O4不均匀地分布在石墨烯膜表面所造成局域浓差有关,并提出了感抗产生的模型。     

高岭石-水体系中水分子结构的分子动力学模拟

以Hendricks模型为初始结构, 利用CLAYFF力场对高岭石-水体系进行无晶体学限制的分子动力学模拟. 结果表明, 层间水有三种类型: I型类似于Costanzo提出的“洞水”分子, 其HH矢量(水分子中从一个氢原子位置指向另一个氢原子位置的方向矢量)平行于(001)平面, 而C2轴稍微倾斜于(001)面法线; II型类似于“连接水”, 一个氢氧键指向临近的层间四面体氧形成氢键, 另一个氢氧键与(001)面近似平行; III型水分子在层间近似保持为竖直状, 一个氢与层间四面体氧形成氢键, 而另一个氢与对面层的羟基氧形成氢键. 高岭石羟基氢沿(001)晶面法线的浓度曲线显示一部分羟基指向变为近似平行于(001)面, 羟基氧因此能够暴露出来与层间水分子氢形成氢键. 此外, 模拟中还观察到部分II型水分子氧偏离于层间的平均位置而更靠近四面体层, 这和Costanzo的实验结果一致, 可能是X射线谱图中(002)弱衍射峰出现的原因.     

Broadband non-polarizing beam splitter based on guided mode resonance effect

A broadband non-polarizing beam splitter (NPBS) operating in the telecommunication C+L band is designed by using the guided mode resonance effect of periodic silicon-on-insulator (SOI) elements. It is shown that this double layer SOI structure can provide ～50/50 beam ratio with the maximum divergences between reflection and transmission being less than 8% over the spectrum of 1.4 μm～1.7 μm and 1% in the telecommunication band for both TE and TM polarizations. The physical basis of this broadband non-polarizing property is on the simultaneous excitation of the TE and TM strong modulation waveguide modes near the designed spectrum band. Meanwhile, the electric field distributions for both TE and TM polarizations verify the resonant origin of spectrum in the periodic SOI structure. Furthermore, it is demonstrated with our calculations that the beam splitter proposed here is tolerant to the deviations of incident angle and structure parameters, which make it very easy to be fabricated with current IC technology.