SAGCM-APD增益影响因子分析与优化

应用二维漂移扩散模型研究具有分立吸收层、渐变层、电荷层和倍增层结构(SAGCM)的InGaAsP-InP雪崩光电探测器(APD),仿真分析了不同电荷层、倍增层厚度和掺杂浓度对电场分布、电流响应及击穿电压的影响,特别是参数变量对增益计算模型的影响,载流子传输过程的时间依赖关系和倍增层中所处位置的影响,仿真结果表明:较高掺杂浓度和较薄电荷层结构可以改变器件内部的电场分布,进而提高增益值.当入射光波长为1.55μm,光功率为500 W/m2时,光电流响应量级在10-2A;阈值电压降低到10V以下,击穿电压为42.6V时,器件倍增增益值大于100.     

无催化剂气相沉积法直接制备用于紫外光检测的氧化锌纳米线网

对于环境检测和高速光通信而言,高性能紫外光电探测器是关键。利用气相沉积法在无催化剂条件下制备氧化锌纳米线网,在纳米线网上直接制备光电器件的性能得到了提高。结果显示,纳米线网光电探测器的光电流为60 A,大约是单根纳米线光电器件光电流的15倍。详细讨论纳米线网光电探测器的响应机制发现,在纳米线网内,纳米线与纳米线之间的结势垒高度决定了纳米线内部载流子的传输。当紫外光照射纳米线网光电探测器时,纳米线与纳米线之间结势磊高度的快速变低,从而提高光电器件的性能。     

纳米结构C_(60)薄膜对TiOPc电荷分离的增强作用

研究了具有纳米结构的C60层对TiOPc电荷分离的影响。以ITO为基底,真空蒸镀TiOPc薄膜,再以真空蒸镀和电泳法分别制备C60薄膜,通过扫描电镜(SEM)观察到电泳法制备的C60电荷分离层表面具有约200μm的微结构。实验表明:TiOPc/C60器件在近红外区间的光电响应曲线与TiOPc的吸收光谱曲线趋向一致,且光伏响应随功率增加呈线性增强;具有纳米结构C60电荷分离界面的器件光电响应比具有平整C60界面的器件强60%左右,其原因在于作为电荷分离区域的TiOPc和纳米结构C60层接触的面积更大,提高了电荷分离的效率。     

胆甾液晶应用于P3HT∶PCBM聚合物光伏器件研究

本研究利用液晶材料的自组装特性,将胆甾醇油酸酯3β-Hydroxy-5-cholestene 3-oleate掺杂有机聚合物太阳能电池活性层P3HT:PC61BM内,制备出不同掺杂比例的光伏器件。实验结果表明,液晶掺杂质量比为0.3%时,器件的光电转换效率最高。说明液晶分子可诱导活性层材料分子在结晶过程中有序排列,减少层内分子团簇,减少活性层薄膜缺陷,形成有效的载流子传输通道。适当的掺杂比例,增大了器件并联电阻和填充因子,器件性能得到改善。     

热处理对活性层性质及有机光伏电池性能的影响

制备了MEH-PPV活性层薄膜及其器件,通过AFM、透射光谱和伏安特性测量研究了热处理对薄膜表面性质及其光电性能的影响。结果表明热处理降低了表面粗糙度,减小了禁带宽度和电阻率,提高了载流子迁移率。薄膜表面性质以及光电性能的优化,有利于增加有机光伏电池的短路电流、开路电压和填充因子,提高其能量转换效率,改善电池的器件性能。     

超晶格雪崩光电二极管的结构优化及性能研究

基于碰撞离化理论研究了异质材料超晶格结构对载流子离化率的作用,设计得到In0.53Ga0.47As/In0.52Al0.48As超晶格结构的雪崩光电二极管。通过分析不同结构参数对器件性能的影响,得到了低隧道电流、高倍增因子的超晶格结构雪崩层,根据电场分布方程模拟了器件二维电场分布对电荷层厚度及掺杂的依赖关系,并优化了吸收层的结构参数。对优化得到的器件结构进行仿真并实际制作了探测器件,进行光电特性测试,与同结构普通雪崩光电二极管相比,超晶格雪崩光电二极管具有更强的光电流响应,在12.5~20 V的雪崩倍增区,超晶格雪崩光电二极管在具备高倍增因子的同时具有较低的暗电流,提高了器件的信噪比。     

基于可见光响应的纳米硒半导体器件

不加入任何表面活性剂、利用溶解-重结晶原理合成了一维结构的Se纳米带,并用XRD,SEM及TEM等方法对产品进行了表征。以单根的硒纳米带为光电响应材料、以银浆为接触电极组装成纳米器件,并对光电响应特性以及光谱响应特性进行了测试。结果表明:在可见光(日光灯)照射下,其对开灯的最快响应时间约为30 ms,关灯时最快衰减时间为50 ms。该纳米器件的光电流对温度有依赖作用,低温下有利于光电流的产生;单色光的波长对纳米器件的光电流及响应时间的影响不同,在单色光谱响应范围内,纳米器件在650 nm处产生的光电流最大,而在350 nm处的响应时间最快。     

基于电荷传输层优化的量子点发光二极管

采用溶液法旋涂薄膜、真空蒸镀铝电极,制备了ITO/PEDOT∶PSS/空穴传输材料/量子点/纳米氧化锌(ZnO Nanoparticles)/Al结构的量子点发光二极管(QLED)器件。对比了不同纳米氧化锌分散剂对器件性能的影响。当用乙醇和乙醇胺分散氧化锌时,对量子点层破坏较小,器件的亮度最高达22 940cd/m2,电流效率达28.9cd/A。研究了在聚乙烯咔唑(PVK)中掺杂不同比例4,4′-环己基二[N,N-二(4-甲基苯基)苯胺](TAPC)器件的发光特性。在PVK中掺杂TAPC材料能够促进器件空穴传输以及电子空穴注入平衡,当PVK∶TAPC=3∶1时,器件的空穴传输层形貌较为平整,亮度较高;当PVK∶TAPC=1∶1时,器件的开启电压最低。通过对器件膜层表面形貌以及电学、光学性能的对比,分析了电荷传输层优化对器件特性改善的原因。     

DMQA浓度对OLEDs光电性能的影响

为了探讨DMQA掺杂浓度对有机发光器件（OLEDs）光电性能的影响,采用器件结构ITO/PEDOT：PSS/TPD/Alq3：DMQA/LiF/Al,在0.28~4.5 wt%范围内改变DMQA的掺杂浓度,考察了器件的光电性能变化。结果显示,随着升高DMQA掺杂浓度,器件表现为电流略有下降,说明DMQA对载流子传输起阻挡或者陷阱作用;器件发光效率下降明显,说明DMQA分子间作用力较强,存在浓度淬灭效应,而且,器件发光光谱在570~610 nm区间存在肩峰,其强度随着DMQA浓度增加逐步增大,据此推断该肩峰来自于DMQA激基缔合物发射。     

用于远红外探测的Si:P阻挡杂质带红外探测器研制

提出了全外延技术方案制备阻挡杂质带薄膜,避免了离子注入制备背电极层影响外延薄膜质量的技术难点.基于硅器件工艺设计制作了Si:P阻挡杂质带红外探测器.测量了器件的光电流响应谱和暗电流特性曲线,指认了叠加在光电流响应谱上的尖锐杂质峰对应阻挡层中磷原子的杂质跃迁.研究了器件在低温下小偏压范围内的暗电流起源.通过对计算结果分析,排除了该区域暗电流起源于热激发电导和跳跃式电导的可能,指出暗电流来自器件对冷屏的光电响应.器件工作温度5 K,工作偏压1.6 V时,响应波段覆盖2.5~40μm,峰值波长28.8μm,峰值响应率20.1 A/W,峰值探测率3.7×1013cm·Hz1/2/W(背景光子通量低于1013ph/cm2·s).     

Improvement of photoelectrochemical and optical characteristics of MEH-PPV using titanium dioxide nanoparticles

The use of bulk heterojunctions can increase the efficiency of exciton dissociation in polymer-based photovoltaics. We prepared and characterized bulk heterojunctions of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and titanium dioxide nanoparticles deposited by spin coating on indium tin oxide substrates. The surface morphology of the MEH-PPV+TiO₂ composite films revealed that addition of TiO₂ nanoparticles increased the film roughness. The effect of TiO₂ nanoparticles on the photoelectrochemical and optical characteristics of MEH-PPV polymer heterojunctions was studied. Addition of TiO₂ nanoparticles improved the absorbance of MEH-PPV composite films. Moreover, the photocurrent of the composite devices increased with the TiO₂ nanoparticle concentration. These observations provide an insight into new approaches to improve the light collection efficiency in photoconductive polymers.     

C60 Concentration Influence on MEH-PPV:C60 Bulk Heterojunction-Based Schottky Devices

We have investigated the effect of C60 concentration on the performance of poly[2-methoxy-5-(2′-ethylhexoxy-p-phenylene vinylene] (MEH-PPV):C60 blend-based Schottky barrier-based devices. Incorporation of C60 in MEH-PPV leads to a red shift and the reduction of intensity in MEH-PPV absorption spectra. The appearance of a C60 characteristic band in the Raman spectra of the composites indicates the presence of C60 in the blends. A FESEM study reveals that the addition of C60 significantly modifies the surface morphology of the blend films. However, higher concentrations (>?5 wt.%) results in agglomeration of C60 particles. Dark I–V measurements allow us to extract various diode parameters including barrier height, ideality factor, and saturation current. Profound variations have been observed in the dominant charge carrier transport mechanism for different C60 concentrations. A photoresponse study demonstrates the enhancement in the photocurrent with the increase in the C60 concentration up to 5 wt.%. Beyond this concentration, agglomeration impedes exciton dissociation and charge transport, which results in a decrease in the photocurrent. Finally, an impedance spectroscopy analysis has been extensively carried out to estimate the internal device parameters, such as junction resistance, capacitance and carrier lifetime. The correlation between these parameters and I–V curves has been established.     

Highly enhanced photoelectric catalysis of WO3 nanoblocks loaded with Ag nanoparticles

WO3/Ag composite film photoanodes were synthesized by hydrothermal combined electrodeposition method. Characterization of samples was conducted by scanning electron microscope (SEM) and X-ray diffraction (XRD), which showed that WO3/Ag composite films had been synthesized. Diffuse reflectance spectra show WO3/Ag composite film has more strong absorption than WO3 film under simulated visible light irradiation. Electrochemical impedance spectroscopy shows WO3/Ag composite film photoanode enhances charge transfer efficiency compared with WO3 film. WO3/Ag composite film photoanodes show higher photocurrent and photoelectric catalytic activity than WO3 film, and the WO3/Ag composite film obtained by depositing Ag nanoparticles at 50 s (WO3/Ag-50) shows the highest photocurrent and photoelectric photoelectric catalytic activity. Meanwhile, the photoelectric catalytic activity of the composite film is higher than their direct photocatalytic and electric catalytic activity. The higher photocurrent and photoelectric catalytic activity of the WO3/Ag composite film photoanodes are attributed to the surface plasmon resonance effect of Ag nanoparticles and Schottky junction effect at the WO3/Ag interface.     

Electrical bistability,negative differential resistance and carrier transport in flexible organic memory device based on polymer bilayer structure

Bistable nonvolatile memory devices containing two different layers of polymers, viz. MEH-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenyl vinylene]) and PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) has been fabricated by a simple spin-coating technique on flexible polyimide (PI) substrates with a structure Al/MEH-PPV/PEDOT:PSS/Ag-Pd/PI. The current–voltage measurements of the as-fabricated devices showed a nonvolatile electrical bistability with electric field induced charge transfer through the polymer layers and negative differential resistance (NDR) which is attributed to the charge trapping in the MEH-PPV layer. The current ON/OFF ratio between the high-conducting state (ON state) and low-conducting state (OFF state) is found to be of the order of 10³ at room temperature which is comparable to organic field effect transistor based memory devices. We propose that such an improvement of rectification ratio (ON/OFF ratio) is caused due to the inclusion of PEDOT:PSS, which serves as a conducting current path for carrier transport; however, NDR is an effect of the trapped charges in the MEH-PPV electron confinement layer. The device shows excellent stability over 10⁴ s without any significant degradation under continuous readout testing in both the ON and OFF states. The carrier transport mechanism of the fabricated organic bistable device has been explained on the basis of different conduction mechanisms such as thermionic emission, space-charge-limited conduction, and Fowler–Nordheim tunneling. A band diagram is proposed to explain the charge transport phenomena. These bilayer structures are free from the drawbacks of the single organic layer based memory devices where the phase separation between the nanoparticles and polymers leads to the degradation of device stability and lifetime.     

有序碳纳米管的光电响应实验

通过实验,研究了720℃时通过化学气相沉积(CVD)法在Si基板上得到的大面积垂直排列的有序多壁碳纳米管(MWNTs)的光电响应特性。实验表明,激光诱导所产生的光电流是光强度和偏置电压的线性函数,其大小取决于所产生的光子载体的漂移速度。     

Modeling anomalous charge carrier transport in disordered organic semiconductors using the fractional drift-diffusion equation

Anomalous transport is ever-present in many disordered organic semiconductor materials. The long-tail behavior observed in the transient photocurrent is a manifestation of anomalous transport. Owing to the fact that anomalous transport has dispersive and non-Gaussian transport dynamics, thus anomalous transport cannot be adequately described by the standard drift-diffusion equation which is a framework commonly used to model normal diffusive transport. In this work, we generalized the standard drift-diffusion equation to time fractional drift-diffusion equation (TFDDE) using the fractional calculus approach to model the anomalous transport in the regio-random poly(3-hexylthiophene) (RRa-P3HT) and regio-regular poly(3-hexylthiophene) (RR-P3HT). Physical elucidation of TFDDE is given by stressing how the influence of the multiple-trapping mechanisms and energy disorder lead to the long-tail behavior in the transient photocurrent curves. TFDDE is solved numerically using finite difference scheme to obtain the profiles of charge carriers density evolution and hence to reproduce the corresponding transient photocurrents of RRa-P3HT and RR-P3HT. Poisson solver is also included in the model to account for the fluctuation of localized electric field due to the evolution of charge carriers. It is found that charge carriers acquire additional energy from high electric field that helps them to escape from the trap centers more easily and then propagating at higher velocity, which yields higher transient current. Higher concentration of charge carriers can be generated at higher light intensity and they can occupy energy levels close to the mobility edge, where charge carriers will encounter smaller capturing rate and hop at a longer length in each hopping event. Thus, the transport dynamic of charge carriers at high light intensity is less dispersive than that of the low light intensity. Besides, the transport dynamic of charge carriers in RR-P3HT is relatively less dispersive and has higher mobility than that of the RRa-P3HT since RR-P3HT has lower capturing rate and is less energy disordered.     

Effect of guest concentration on carrier transportation in blends of conjugated polymers

In this paper, the charge transport in pure poly (9,9-dioctylfluorene-2, 7-diyl) (PFO) and its blend with poly (5-methoxy-2-2-ethyl-hexylthio)-p-phenylenevinylene (MEH-PPV) is studied. The mobility (μ_eff) and diffusivity (D) of the pure and blend thin films have been calculated using electroluminescence transient (ELT) technique. MEH-PPV concentration was varied from 0.8 to 15 wt%. It is found that at relatively low concentration of MEH-PPV, less than 1.2 wt%, the mobility of PFO:MEH-PPV blend increases with the concentration of MEH-PPV, and after that, it starts decreasing. The field dependence of effective hole mobility follows the Poole–Frenkel (P–F) plot of mobility (μ) as a function applied electric field with positive slope (β_PF > 0) up to 5.0 wt% concentration of MEH-PPV. A negative P-F type dependence is then observed for 8.0–15 wt% MEH-PPV concentration. Diffusivity (D) of blends is following the same trends as mobility i.e. blend with 1.2 wt% MEH-PPV shows the highest diffusivity. These results have been correlated with the morphology of pure and blend thin films. Gaussian Disorder Model (GDM) alone is not able to explain the change in β_PF with the MEH-PPV concentration, guest induced crystallization of PFO plays an important role at low concentrations of MEH-PPV. At higher concentrations of MEH-PPV (≥8 wt%), crystallization is suppressed, and position disorder induced behavior of polymer determines the charge transport in the blends.     

核-壳结构ZnO@CuO光阳极的制备及其光电性能研究

ZnO是钙钛矿太阳电池(PSCs)电子传输层(ETL)的优良材料,但ZnO与钙钛矿吸收层界面有很大的热不稳定性,从而导致该界面严重的电荷复合。文章采用水热法在FTO导电玻璃上制备出具有良好取向性的ZnO纳米棒阵列(NAs)。通过调控电化学沉积时间,在ZnO NAs上沉积一层CuO纳米颗粒,获得ZnO@CuO纳米复合材料薄膜。利用场发射扫描电镜(FESEM)、X射线衍射(XRD)对复合薄膜的形貌和物相进行了观察和分析。通过紫外-可见光漫反射(UV-Vis DRS)和瞬态荧光光谱(PL)对其光学性能进行了测定。结果表明,制备的ZnO NAs阵列均匀且垂直度较好,直径约为120 nm;通过电化学沉积CuO纳米颗粒(尺寸为34～44 nm)后,复合薄膜的可见光吸收能力增强,载流子分离效率提高;在电化学沉积时间为40 s时,所得到的ZnO@CuO NAs的光电流密度最高,约为ZnO NAs的3.37倍,表现出良好的光电转换性能。     

Effect of low-temperature interphase charge transport at the Si/SiO2 interface on the photoresponse of silicon barrier structures

The effect of low-temperature electron charge redistribution at the Si/SiO₂ interface between the interphase states and the conduction band of an n-Si crystal on the temperature behavior of conductance, photovoltage, and photocurrent in Si barrier structures with edge surface electron channels was studied in the temperature range of 77–300 K. The dynamics of the channel-current response to the voltage changes in the dark and under illumination can be explained qualitatively by dispersive hopping transport of holes in SiO₂, which induces electron transfer to, and accumulation at, the Si surface near the barrier contact. The leveling off of the photovoltage at low temperatures and the nonmonotonic temperature dependence of the photocurrent are attributed to the nonmonotonically increasing, localized hole density at the Si/SiO₂ interface and the free electron density at the Si surface with decreasing temperature, which reflects changes in the valence of oxygen complexes.     

Charge transport in poly(p-phenylene vinylene) at low temperature and high electric field

Charge transport in poly(2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV)-based hole-only diodes is investigated at high electric fields and low temperatures using a novel diode architecture. Charge carrier densities that are in the range of those in a field-effect transistor are achieved, bridging the gap in the mobility versus charge carrier density plot between polymer-based light-emitting diodes and field-effect transistors. The extended field range that is accessed allows us to discuss the applicability of current theoretical models of charge transport, using numerical simulations. Finally, within a simple approximation, we extract the hopping length for holes in MEH-PPV directly from the experimental data at high fields, and we derive a value of 1.0 ± 0.1 nm.