CH3NH3PbI3和CH3NH3MnI3的电子结构和光学性质研究

采用第一性原理计算,研究了有机金属卤化物钙钛矿CH₃NH₃PbI₃和CH₃NH₃MnI₃的电子结构、磁性和光吸收。CH₃NH₃PbI₃和CH₃NH₃MnI₃都是具有直接带隙半导体,CH₃NH₃MnI₃磁基态为G型反铁磁序(G-AFM)。CH₃NH₃MnI₃在G-AFM状态下的带隙值为1.668 eV;当系统处于FM态时,多数自旋通道的带隙为0.696 eV,少数自旋通道的带隙为2.148 eV。结果表明,具有FM态的CH₃NH₃MnI₃的光激发电子将迅速熔化局域磁序。最后计算了CH₃NH₃PbI₃和CH₃NH₃MnI₃的光学特性,结果表明具有铁磁态的CH₃NH₃MnI₃(FM)表现出较强的红外光吸收。     

CH3NH3PbI3钙钛矿薄膜阵列光电探测器

将光电性能优异、可通过低温溶液法制备的卤化物钙钛矿制成阵列型光电探测器,必将推动其在成像、光通信等领域中的应用。然而,卤化物钙钛矿易被常规溶剂(包括显影液)溶解,导致其与光刻工艺不兼容。自组装单分子疏水层结合光刻工艺的亲水-疏水图形基底制备方法能解决制备过程中极性溶剂与钙钛矿材料不兼容的问题,通过简单的旋涂(极性钙钛矿前驱体溶液仅在亲水图形区域浸润)、低温退火,可以快速获得钙钛矿阵列。CH₃NH₃PbI₃薄膜阵列光电探测器具有良好的光电性能, 530 nm光辐照下探测率为4.7×10¹¹ Jones,响应度为0.055 A/W。这项工作为制备图案可控的钙钛矿薄膜阵列光电探测器提供了一种简单而有效的策略。     

PbI2对钙钛矿薄膜及太阳电池性能的影响

碘化铅(PbI₂)是两步法制备钙钛矿薄膜最常使用的金属卤化物前驱体,精确控制PbI₂在钙钛矿薄膜中的含量和空间分布以及优化PbI₂薄膜的形貌结构对于制备高效稳定的太阳电池具有重要意义。探索了PbI₂的浓度和退火方式对钙钛矿薄膜及太阳电池性能的影响。研究发现,PbI₂溶液的浓度不仅决定钙钛矿薄膜中PbI₂的含量,也影响钙钛矿的晶粒尺寸、取向及光学吸收等性质,从而导致器件性能的改变,当钙钛矿薄膜表面分布约45%的PbI₂时器件性能更佳。此外,PbI₂的形貌、结晶性和孔隙度受退火方式的影响显著,与溶剂退火相比,通过短暂的1 min热退火制备的PbI₂薄膜更有利于减少钙钛矿表界面缺陷,提升器件的开路电压,最终使器件的基础光电转换效率(PCE)可以提升至20.89%。上述研究结果有助于进一步优化钙钛矿太阳电池制备工艺,提升器件性能。     

CH3NH3PbI3钙钛矿太阳电池晶粒尺寸及光电性能调控

钙钛矿薄膜的晶粒尺寸对器件性能影响很大。采用湿润性不同的空穴传输层以及不同浓度的CH3NH3I（MAI）溶液,使用热退火和溶剂气氛退火的方法制备出CH3NH3PbI3薄膜及相应电池。测量了不同制备条件的钙钛矿薄膜的X射线衍射、扫描电子显微镜、光致发光谱,以及器件的电流密度-电压曲线。结果表明,溶剂气氛退火可以有效地增大薄膜的晶粒尺寸,提高器件的电流密度;较高浓度的MAI能将PbI2完全转化为CH3NH3PbI3,增大晶粒尺寸;不湿润的功函数更高的空穴传输层有利于电池效率的提高。制备了最高效率为13.3%的CH3NH3PbI3钙钛矿电池,为制备更大晶粒的钙钛矿薄膜与更高效率的钙钛矿太阳电池奠定了基础。     

磁控溅射氧氩体积流量比对β-Ga2O3薄膜的影响

利用射频磁控溅射在c面单晶蓝宝石(Al₂O₃)衬底上制备Ga₂O₃薄膜,研究了溅射过程中通入氧气与氩气的体积流量比对经过异位高温后退火处理得到的β-Ga₂O₃薄膜特性的影响。利用X射线衍射仪(XRD)和原子力显微镜(AFM)对薄膜进行表征,结果表明β-Ga₂O₃薄膜沿着■晶面择优生长,具备较好的单一取向性。在氧氩体积流量比约为1∶20时,薄膜的结晶性能相对较好、表面晶粒分布较均匀、均方根粗糙度较小、晶粒尺寸较大。此外,吸收光谱表征结果表明,不同氧氩体积流量比下制备得到的β-Ga₂O₃薄膜的带隙变化范围为4.53～4.64 eV,在较低氧氩体积流量比下制备的β-Ga₂O₃薄膜表现出较优的光学性质,在波长200～300 nm内具有较好的吸收特性,表现出良好的深紫外光学特性。     

快速响应的垂直结构二维钙钛矿光电探测器

制备基于二维钙钛矿(PEA)₂(MA)₄Pb₅I₁₆[PEA为C₆H₅(CH₂)NH₃, MA为CH₃NH₃]的垂直结构光电探测器,当二维钙钛矿薄膜厚度为280 nm时,器件的亮电流最大,500 nm处外量子效率达到90%,响应率达到0.37 A/W,探测率达到3.4×10¹² Jones(1 Jones=1 cm·Hz^1/2/W)。当二维钙钛矿薄膜厚度减小时,器件的响应时间没有持续减小,而在其厚度为80 nm时器件的响应时间最短,这是受载流子渡越时间和钙钛矿薄膜质量双重影响下的结果。在二维钙钛矿薄膜厚度为80 nm的基础上,通过减小器件的有效面积,其最终实现了113 ns的响应时间。本工作对推动低成本快速响应光电探测器的发展有着重要意义。     

GaAs衬底上β-Ga2O3纳米点阵薄膜的MOCVD制备

将热氧化与MOCVD工艺相结合,总结了一种在本征GaAs衬底上进行β-Ga₂O₃纳米点阵薄膜制备的工艺,该工艺不涉及金属催化剂与复杂刻蚀,工艺更为简单。使用扫描电子显微镜对所制备薄膜的形貌特征进行了表征与分析,发现所制备的纳米点阵薄膜呈现五方的柱状结构。对所制备样品进行了X射线衍射、拉曼振动、光致发光谱的测试,结果表明薄膜的晶体质量随着MOCVD生长温度与Ⅵ/Ⅲ比的提高而得到优化。使用有限元法（FEM）仿真验证了β-Ga₂O₃纳米点阵薄膜制备的高陷光特点。     

原子层沉积低温生长α-MoO3薄膜

以六羰基钼和氧气为前驱体,通过等离子增强原子层沉积技术（PE-ALD）在硅基片上实现了α-MoO₃薄膜的低温制备。利用X射线衍射仪、扫描电子显微镜、原子力显微镜、X射线光电子能谱仪等手段对薄膜的晶体结构、表面形貌及薄膜成分进行表征和分析。研究发现衬底温度和氧源脉冲时间对MoO₃薄膜的晶体结构和表面形貌变化起关键作用。当衬底温度为170℃及以上时所制备的薄膜为α-MoO₃;适当延长ALD单循环中的氧源脉冲时间有利于低温沉积沿（0k0）高度择优取向的MoO₃薄膜。根据对不同厚度MoO₃薄膜表面的原子力显微图片分析,MoO₃薄膜为岛状生长模式。     

WO3/SnO2复合薄膜的制备及光电性能

采用水热法和电化学沉积法,成功制备了包覆有SnO₂纳米颗粒的WO₃纳米棒阵列薄膜,退火处理后形成WO₃/SnO₂异质结复合薄膜。通过改变SnO₂的沉积时间得到了复合薄膜的最佳制备条件。采用XRD,FESEM对WO₃/SnO₂复合薄膜的物相和形貌进行了分析,通过电化学工作站对WO₃/SnO₂复合薄膜的光电性能进行了研究,结果表明,电沉积时间为120 s时,WO₃/SnO₂复合薄膜具有最小的阻抗,且在0.6 V的偏压下光电流密度为0.46 mA/cm²,相比于单一WO₃纳米棒薄膜,表现出更好的光电化学性能。     

磁控溅射工作压强对β-Ga2O3薄膜特性的影响

作为新兴的第三代半导体材料,β-Ga₂O₃高质量薄膜是制备高效Ga₂O₃基器件的基础,β-Ga₂O₃薄膜的制备、表征及光电特性的研究具有深刻的意义。通过分析研究磁控溅射工作压强变化对薄膜性能和形貌的影响,为制备更高质量的薄膜提供了一种新的方法。基于射频磁控溅射方法,在单晶c面蓝宝石(Al₂O₃)衬底上沉积生长Ga₂O₃薄膜,并进行900℃、90min的氮气退火处理,以得到β-Ga₂O₃薄膜。沉积过程不改变其他实验参数,仅改变工作压强,研究工作压强对β-Ga₂O₃薄膜特性的影响。X射线衍射仪(XRD)和原子力显微镜(AFM)表征结果显示,β-Ga₂O₃薄膜具有不同取向的衍射峰,沿着■晶向择优生长,薄膜呈多晶状态。适当增大工作压强可使β-Ga<...     

Novel polycrystalline silicon thin film transistors prepared by deposition from Si2H6 and subsequent annealing by NH3 plasma

This work investigated the channel layer of polycrystalline silicon (poly-Si) thin film transistors (TFTs) prepared by amorphous silicon (a-Si) films deposited using Si₂H₆ gas. The recrystallization of channel layers, source/drain, gate electrodes and post implant anneal were performed at the same time. Due to the larger grain size, the device has higher field effect mobility than SiH₄ deposited devices. These devices were also subsequently passivated by NH₃ plasma. The NH₃ plasma significantly improves the n-channel devices; however, the improvement of p-channel devices is limited. Especially, the threshold voltage of n-channel devices is significantly shifted toward the negative gate voltage than the shift magnitude of p-channel devices. To investigate the band gap width and Fermi level by determining the leakage activation energy, it is found that the channel film is changed slightly from p-type to n-type. These results may be attributed to the donor effect by NH₃ plasma passivation.     

原子层沉积方法制备低温多层Al2O3/TiO2复合封装薄膜的研究

原子层沉积(ALD)方法可以制备出高质量薄膜,被认为是可应用于柔性有机电致发光器件(OLED)最有发展前景的薄膜封装技术之一。本文采用原子层沉积(ALD)技术,在低温(80℃)下,研究了Al₂O₃及TiO₂薄膜的生长规律,通过钙膜水汽透过率(WVTR)、薄膜接触角测试等手段,研究了不同堆叠结构的多层Al₂O₃/TiO₂复合封装薄膜的水汽阻隔特性,其中5 nm/5 nm×8 dyads(重复堆叠次数)的Al₂O₃/TiO₂叠层结构薄膜的WVTR达到2.1×10^-5 g/m²/day。采用优化后的Al₂O₃/TiO₂叠层结构薄膜对OLED器件进行封装,实验发现封装后的OLED器件在高温高湿条件下展现了较好的寿命特性。     

Smooth indium zinc oxide film prepared by sputtering a In2O3:ZnO=95:5 target

Indium zinc oxide (IZO) films with surface roughness Ra<0.3 nm have been prepared by radio frequency sputtering. The IZO film is the possible candidate for replacing the indium tin oxide (ITO) film in pattern precision or low processing temperature concern. Instead of commonly used In₂O₃:ZnO=90:10 in weight percentage (wt%) target, a target doped with 5 wt% impurities was used in this study. It was found that the electrical resistivity of the IZO film increases rapidly if oxygen gas was introduced during the sputtering process. This increase tendency in electrical resistivity is much more significant than the IZO film prepared with a 10 wt% doped ZnO target. The electrical resistivity increased rapidly as soon as the IZO film became crystallized in heat treatment. Optical properties of the IZO film do not change significantly with varying process parameters. The appropriate processing condition for the prepared IZO film is no oxygen feeding and no heat treatment.     

Pr3+掺杂SrTiO3薄膜的聚合物前驱体法制备及发光性能

采用聚合物前驱体法,在LaNiO<,3>/si(100)衬底上低温制备了Pr<,3+>掺杂SrTiO<,3>薄膜.用XRD,AFM、PL手段分析了薄膜的晶体结构、表面形貌与发光性能.结果显示,退火温度决定SrTiO<,3>薄膜的晶粒大小和表面形貌,在600℃退火2 h获得的薄膜表面均匀、无裂痕,晶粒大小约为60 nm,...     

A novel method for a smooth interface at poly-SiOx/SiO2 by employing selective etching

We have investigated the excimer laser recrystallization of slightly oxygen-added amorphous silicon (a-SiO_x) films for the application to the active layer of thin film transistors. We also propose a new method to reduce the surface roughness of poly-SiO_x films by etching the grain boundaries selectively. SEM images show that the Si-O bonds are well segregated into the poly-Si grain boundaries after laser crystallization and the surface morphology is remarkably improved after the selective buffered oxide etchant (BOE) etching of the grain boundaries. The electrical conductivity measurement shows that the activation energies of poly-SiO_x and poly-Si films have an identical value of 0.52 eV. This may confirm that oxygen-induced defects do not cause any difference in the electrical performance even at the oxygen concentration of 0.18 at.%. Moreover, the electrical mobility and subthreshold slope of poly-SiO_x TFTs are considerably improved by employing the proposed method, which smooths the poly-SiO_x/SiO₂ interface     

Critical current characteristics of YBa2Cu3O7 thin films on (110) SrTiO3

The material and electrical characteristics of YBa₂Cu ₃O₇ (YBCO) thin films deposited by inverted cylindrical magnetron sputtering on (110) SrTiO₃ (STO) were investigated. X-ray diffractometry shows the grain orientations to be predominantly the YBCO (110) and (103) with no evidence of c-axis grains, Electron micrographs show the film surface to consist of coupled elongated grains parallel to the (110) STO edge. The films were patterned into small 2.5 mm squares parallel to the substrate edges for electrical characterization. Transport currents parallel and perpendicular to the (110) substrate edge showed a 945:1 anisotropy in film resistance and a factor of two in critical current density for temperatures below 60% of the transition temperature (T_c). The temperature dependence of the critical current near T_c was quadratic-like and strongly dependent on the value of T_c used in the analysis. For the two orientations, there was nearly a 6 K difference in T_c as determined by the point at which the critical current became zero. The response of the critical current to small magnetic fields was greater for transport current along the c-axis direction and was observable over a temperature interval nearly four times greater than for current along the basal plain. These YBCO thin films have good response to small magnetic fields and are suitable for vortex flow device development     

Passivated Perovskite Crystallization via g‐C3N4 for High‐Performance Solar Cells

Organometallic halide perovskite films with good surface morphology and large grain size are desirable for obtaining high‐performance photovoltaic devices. However, defects and related trap sites are generated inevitably at grain boundaries and on surfaces of solution‐processed polycrystalline perovskite films. Seeking facial and efficient methods to passivate the perovskite film for minimizing defect density is necessary for further improving the photovoltaic performance. Here, a convenient strategy is developed to improve perovskite crystallization by incorporating a 2D polymeric material of graphitic carbon nitride (g‐C₃N₄) into the perovskite layer. The addition of g‐C₃N₄ results in improved crystalline quality of perovskite film with large grain size by retarding the crystallization rate, and reduced intrinsic defect density by passivating charge recombination centers around the grain boundaries. In addition, g‐C₃N₄ doping increases the film conductivity of perovskite layer, which is beneficial for charge transport in perovskite light‐absorption layer. Consequently, a champion device with a maximum power conversion efficiency of 19.49% is approached owing to a remarkable improvement in fill factor from 0.65 to 0.74. This finding demonstrates a simple method to passivate the perovskite film by controlling the crystallization and reducing the defect density.     

Epitaxial growth of β-SiC on Si by RTCVD with C3H8 and SiH4

The authors established that β-SiC thin films can be grown epitaxially on (100) Si substrates by rapid thermal chemical vapor deposition (RTCVD) employing carbonization with C₃H₈ , as well as post-carbonization growth using SiH₄ and C ₃H₈ in H₂. They determined the optimum carbonization conditions with respect to reaction temperature and ramp rate, gas flow rates, etc. A possible mechanism, based on nucleation density and Si surface diffusion, has been proposed for the effect of C ₃H₈ flow rate in film thickness, morphology, and void formation. Void-free SiC films have been grown on Si at high C₃H₈ flow rates. The authors determined the optimum conditions for subsequent SiC growth with respect to temperature and Si/C ratio in the gas phase. They established that the resulting SiC thin films are monocrystalline by X-ray and electron diffraction. The SiC-Si interface was investigated by cross-section transmission electron microscopy and found to be sharp and intimate where no voids are present