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1.
    
Charge transport governs the operation and performance of organic diodes. Illuminating the charge‐transfer/transport processes across the interfaces and the bulk organic semiconductors is at the focus of intensive investigations. Traditionally, the charge transport properties of organic diodes are usually characterized by probing the current–voltage (I–V) curves of the devices. However, to unveil the landscape of the underlying potential/charge distribution, which essentially determines the I–V characteristics, still represents a major challenge. Here, the electrical potential distribution in planar organic diodes is investigated by using the scanning Kelvin probe force microscopy technique, a method that can clearly separate the contact and bulk regimes of charge transport. Interestingly, by applying to devices based on novel, high mobility organic materials, the space‐charge‐limited‐current‐like I–V curves, which are previously believed to be a result of the bulk transport, are surprisingly but unambiguously demonstrated to be caused by contact‐limited conduction. A model accounting is developed for the transport properties of both the two metal/organic interfaces and the bulk. The results indicate that pure interface‐dominated transport can indeed give rise to I–V curves similar to those caused by bulk transport. These findings provide a new insight into the charge injection and transport processes in organic diodes.  相似文献   

2.
    
Photo-generated charge behaviors in the bulk heterojunctions (BHJs) of all-polymer solar cells (PSCs) are studied by Kelvin probe force microscopy (KPFM). Root-mean-square deviations (RMSDs, Rq) of the contact potential difference (CPD) images are applied to quantitatively characterize the phase segregations of the BHJs. When the BHJs are illuminated, CPD values and Rq of CPD images are changed, which attributes to the photo-generated charge transfer and accumulation. Inner structures of the BHJ are thus extrapolated by studying the charge behaviors, demonstrating KPFM an effective technique to study the relationship between inner structures and photovoltaic activities in all-PSCs.  相似文献   

3.
    
Charge transfer at the hetero-interface is at the center of van der Waals (vdWs) heterostructure devices for multi-functional applications. Compared with the extensively investigated photogenerated carrier transfer driven by the built-in electric field from the conduction or valence band offset, the charge transfer due to the Fermi level difference of the two adjacent constitutes, and its influence on the opto-/electronic performance of vdWs heterostructure devices are not clarified. Herein, by taking an example of WSe2/InSe heterostructure, it is demonstrated that the charge transfer at the hetero-interface is an efficient “doping” strategy to dramatically modulate the carrier densities of atomically thin counterparts due to the extension of “band bending” across the entire heterostructure, paving the way for the creation of lateral WSe2 p-n and n-n+ homo-junctions with multi-functionalities, including promising rectification, photovoltaic, and photodetection abilities. Moreover, the device physics of lateral homo-junctions, including potential distribution, band diagram, and photocurrent generation mechanisms, is revealed by gate-dependent Kelvin probe force microscopy and scanning photocurrent measurements. This work not only provides a general avenue to build 2D lateral homo-junctions, but also give deeper insights into the device physics of the junctions by coupling scanning probe and scanning photocurrent techniques.  相似文献   

4.
    
Surface structural, electronic and electrical properties of the quaternary alloy AlInGaN/GaN heterostructures are investigated. Surface termination, atomic arrangement, electronic and electrical properties of the (0001) surface and (10–11) V-defect facets have been experimentally analyzed using various surface sensitive techniques including spectroscopy and microscopy. Moreover, the effect of sub-band gap (of the barrier layer) illumination on contact potential difference (VCPD) and the role of oxygen chemisorption have been studied.  相似文献   

5.
The electrons and holes were injected into the blend electrets of polystyrene and C60 (PS/C60) by adjusting the biases of conductive atomic force microscopy probe. We visualized the charges trapping, release, diffusion, and retention processes of the PS/C60 electrets by utilizing the Kelvin Probe Force Microscopy (KPFM), and found that the localization and retention abilities of the ambipolar charges are enhanced with the increase of C60 content, indicating that blending C60 in PS matrix is a promising method for the charge trapping layer in transistor memory devices. Furthermore, we discussed the storage and diffusion mechanisms, and speculated that the interface of C60 and PS in the blend electrets and repulsive force between charge clusters around C60 are the important factors for the novel storage effect of the blend electret.  相似文献   

6.
    
Halide perovskite-based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole-selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open-circuit voltage of 0.9 V with 18 µW cm−2 under 200 lux (cool white light-emitting diodes). An appropriate post-deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p-type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole-selective layer-deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device.  相似文献   

7.
    
Ionicity plays an important role in determining material properties, as well as optoelectronic performance of organometallic trihalide perovskites (OTPs). Ion migration in OTP films has recently been under intensive investigation by various scanning probe microscopy (SPM) techniques. However, controversial findings regarding the role of grain boundaries (GBs) associated with ion migration are often encountered, likely as a result of feedback errors and topographic effects common in to SPM. In this work, electron microscopy and spectroscopy (scanning transmission electron microscopy/electron energy loss spectroscopy) are combined with a novel, open‐loop, band‐excitation, (contact) Kelvin probe force microscopy (BE‐KPFM and BE‐cKPFM), in conjunction with ab initio molecular dynamics simulations to examine the ion behavior in the GBs of CH3NH3PbI3 perovskite films. This combination of diverse techniques provides a deeper understanding of the differences between ion migration within GBs and interior grains in OTP films. This work demonstrates that ion migration can be significantly enhanced by introducing additional mobile Cl? ions into GBs. The enhancement of ion migration may serve as the first step toward the development of high‐performance electrically and optically tunable memristors and synaptic devices.  相似文献   

8.
    
Next‐generation memory and energy harvesting devices require a higher output performance for charging lectric devices. Generally, it is very limited to control charge transfer through triboelectricity in triboelectric materials. Here, using ferroelectric polarization, it is found that both the amount and direction of charge transfer in triboelectric materials can be controlled. The ferroelectric‐dependent triboelectricity in a ferroelectric co‐polymer film is explored using atomic force microscopy (AFM). Ferroelectric surfaces are rubbed with the AFM tip after poling with positive and negative bias voltages to achieve a triboelectric effect. The surface potential of the positively (negatively) poled area becomes smaller (larger) after rubbing the film surface with the AFM tip. Furthermore, the power output from the triboelectric nanogenerator is dependent on the ferroelectric polarization state. The results indicate that the amount and direction of the charge transfer in triboelectricity can be controlled by the ferroelectric polarization state.  相似文献   

9.
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10.
    
Charge trapping is one of several factors that limit the performance of organic electronic materials, yet even in pentacene, a prototypical small‐molecule semiconductor, the precise chemical nature of charge trapping remains poorly understood. Here the effects of three chemical trap‐precursor candidates are examined by layering thin‐film pentacene transistors with different pentacene defect species. The resulting charge trapping is studied in each device via scanning‐probe electric force microscopy coupled with variable‐wavelength sample illumination. Firstly, it is found that layering with pentacen‐6(13H)‐one (PHO) readily produces uniform charge trapping everywhere in the transistor channel, as expected for an active blanket‐deposited trap‐precursor. However, layering with 6,13‐dihydropentacene (DHP) produces fewer, more‐isolated traps, closely resembling the surface potential distribution in pristine pentacene thin films. Secondly, the rates of trap‐clearing versus illuminating wavelength (trap‐clearing spectra) are measured, revealing enhanced trap‐clearing rates at wavelengths assigned to the absorption of either pentacene or the charged trap species. The trap‐clearing spectrum for the PHO‐layered sample closely resembles the spectrum obtained from pentacene aged in a working transistor, while the trap‐clearing spectrum for the DHP‐layered sample resembles the spectrum observed in pristine pentacene. We conclude that PHO competently creates traps in pentacene that match the expected trap‐clearing spectrum for degraded pentacene, while DHP does not, and that the chemical trap species in aged pentacene is very likely PHO+.  相似文献   

11.
    
In this work, by coupling scanning Kelvin probe force microscopy (SKPM) and photoconductive atomic force microscopy (pcAFM), the variation of the surface potential, photogenerated voltage, and photocurrent networks of the perovskite solar cells (PSCs) with different film topography is studied. The nanoscale photovoltaic reaction of different perovskite capping layers with three different perovskite crystalline sizes is first studied by using the SKPM technique. The performance of the overall device is correlated with the local nanostructure of the perovskite film. Photocurrent maps under various applied voltages are also presented. The pcAFM measurements on three different morphology positions determine that the defect region on the capping layer can induce the charge recombination process in the complete PSCs and thus suppress the Voc in the complete device. These results suggest that the performance of PSCs can still be improved through better control of morphology. Henceforth, SKPM coupled with pcAFM techniques has the potential to become a routine characterization tool for perovskite organic and hybrid photovoltaics.  相似文献   

12.
    
Sulfur is extensively used to increase the bandgap of Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells and to improve the open circuit voltage (VOC ) in order to optimize the characteristics of the devices. This study uses a sulfurization process to obtain a double‐graded bandgap profile. Selenization was carried out on Cu(In,Ga) precursors, followed by one sulfurization process or two consecutive sulfurization processes on top of the CIGSe absorber layer surface. The optimum two‐step sulfurization process provides an increase of VOC of 0.05 V and an improvement of conversion efficiency of 1.17%. The efficiency of the 30 × 30 cm2 monolithic module, which has 64 CIGS cells connected in series (aperture area: 878.6 cm2), is 15.85%. The optical and electrical properties of the phase and the work function distribution were investigated using the depth profiles of the absorber layer as a function of the sulfurization conditions. The CIGSSe thin film formed by two‐step sulfurization with a high sulfur concentration exhibits a single work function peak, better crystallinity, and higher conversion efficiency than those of the thin film formed by two‐step sulfurization at low sulfur concentration. In terms of the Raman spectra depth profile, the phase areas for the CIGSSe thin film that underwent the optimized high sulfur concentration two‐step‐sulfurization appeared to have less of Cu2‐xSe phase than that with low sulfur concentration. Consequently, surface and interface phase analysis is an essential consideration to improve cell efficiency. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

13.
    
Conjugated polyelectrolytes (CPEs) are polymer semiconductors whose properties are affected by the presence of covalently fixed and mobile ions. These structural components lead to interfacial dipoles, electrochemical doping, and mixed ionic and electronic conductivity. While the behavior of ionic carriers is important to a number of CPE applications, it remains difficult to quantify ion transport in films due to interference from electronic carriers; relationships between molecular structure and ion conductivity are thus not well understood. This work demonstrates direct observation of ions in six different CPE films using Kelvin probe force microscopy. Surface potential measurements of thin, planar CPE device structures are used to map the distribution of ions through the simple electrostatic relationship between potential and charge density. The transport of mobile ions within the CPE bulk can be studied through the time‐dependent relaxation of bias‐stressed CPE films, through which the decay of ion populations near each electrode is measured and carefully modeled, leading to estimated values of ionic mobility and effective ionic carrier density. The results show that ion transport is most strongly impacted by the number of ion‐bearing side chains per monomer, which facilitate room temperature ion transport via vibrational motion.  相似文献   

14.
Charge retention of Si nanocrystals elaborated by ultra-low energy ion implantation and thermal annealings into a thin SiO2 layer is characterized by atomic force microscopy (AFM) and Kelvin force microscopy (KFM). Electrons and holes are injected under ambient conditions by applying different bias to a conductive AFM tip in contact with the grounded sample. A surface potential mapping of the sample by KFM is continuously carried out after charge injection. The temporal decay of injected charges and their corresponding lateral spreading are quantified. The results show that the presence of Si nanocrystals leads to a strong charge confinement.  相似文献   

15.
碳纳米管原子力显微镜针尖的研究进展   总被引：3，自引：0，他引：3  
碳纳米管具有很小的半径、较高的纵横比、高的柔软性能、独特的化学结构和确定的电子特性，这一系列性质使得它很适合用作原子力显微镜针尖。针尖的制作原先是手工操作，目前应用较广泛的是化学汽相沉积法（CVD）。这种针尖使朱子力显微镜的分辨率得到很大的提高，纳米操纵能力大大加强。  相似文献   

16.
    
HfO2-based ferroelectric materials are promising candidates for next-generation nonvolatile memories. Since the first report on Si-doped HfO2 ferroelectric thin film in 2011, it has been confirmed that various dopants can induce ferroelectricity in HfO2-based films, and the “wake-up” effect in HfO2 films with different dopants deposited by different processes has been studied extensively. Recent developments in the wake-up effect of doped HfO2-based films are presented. Aside from the differences between the various ferroelectric materials and their deposition methods, the electrodes used in a ferroelectric capacitor, which determine the nature of the interface between the electrode and the ferroelectric layer, can strongly influence the characteristics of the wake-up effect. The rate of variation of the remanent polarization shows certain trends with different dopants. Based on the wake-up mechanisms, many methods to optimize and control this effect are presented in this letter. Until now, the reported mechanism explanations of the wake-up effect all aimed at one type of specific dopant or deposition technique, but can't systematically interpret why the root causes might be different with different dopants and deposition processes. There is also a lack of in-depth research on the effects of interfacial layer with respect to different electrode material.  相似文献   

17.
    
Exciton dissociation at the zinc oxide/poly(3‐hexylthiophene) (ZnO/P3HT) interface as a function of nitrogen doping of the zinc oxide, which decreases the electron concentration from approximately 1019 cm?3 to 1017 cm?3, is reported. Exciton dissociation and device photocurrent are strongly improved with nitrogen doping. This improved dissociation of excitons in the conjugated polymer is found to result from enhanced light‐induced de‐trapping of electrons from the surface of the nitrogen‐doped ZnO. The ability to improve the surface properties of ZnO by introducing a simple nitrogen dopant has general applicability.  相似文献   

18.
计算了放射源在半导体中沿厚度方向的能量沉积,并以此计算β辐射伏特效应电池的理想短路电流。通过对比实测短路电流和理想短路电流可以得到β辐射伏特效应电池PN结内建电场的扩散长度。在上述基础上,本文给出了β辐射伏特效应电池内建电场厚度设计原则： 放射源在半导体中能量沉积厚度和PN结内建电场中载流子的扩散长度两者中较小的应作为β伏特效应电池内建电场厚度设计值,如果沉积厚度远远大于载流子扩散长度,则说明多结结构较适合该类β伏特效应电池果,多结的结数应约为沉积厚度与载流子扩散长度的比。  相似文献   

19.
耦合GaN/AlxGa1-xN量子点的非线性光学性质   总被引：1，自引：1，他引：0  
在有效质量和偶极矩近似下,考虑了由于压电极化和自发极化所引起的内建电场和量子点的三维约束效应,对纤锌矿对称Al_xGa_(1-x)N/GaN/Al_xGa_(1-x)N/GaN/Al_xGa_(1-x)N圆柱型应变耦合量子点中激子非线性光学性质进行了研究。计算结果表明,内建电场使吸收光谱向低能方向移动,发生红移现象,并且使吸收峰强度大大减小。量子限制效应使光吸收峰强度随着量子点尺寸的减小而增强,并且随着量子点尺寸的减小,吸收光谱发生蓝移现象。  相似文献   

20.
《Organic Electronics》2014,15(1):211-215
The understanding of the charge carrier transport in electronic materials is of crucial interest for the design of efficient devices including especially the restraints that arise from device miniaturization. In this work the performance of organic thin-film and single crystal field-effect transistors with the same active material was studied in detail focusing on the high current density regime, where a pronounced non-hysteretic maximum in the transconductance was found. Interestingly, in this operation mode for both, thin films and single crystals, comparable densities of free and gate-induced charge carriers were estimated. Kelvin probe microscopy was used to measure the contact potential difference and the electrical field along the transistor channel during device operation exhibiting the formation of local space charges in the high current density regime.  相似文献   

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