Organic Interfacial Layer Research Articles

Solution-processed, inverted organic solar cells with bilayered inorganic/organic electron extraction layers

High-mobility, solution-processed CdS films were investigated as electron transport layers in inverted, organic solar cells and found to yield excellent performance in conjunction with organic interfacial dipole layers.

Improved amplified spontaneous emission of organic gain media with metallic electrodes by introducing a low-loss solution-processed organic interfacial layer

Improved amplified spontaneous emission has been demonstrated by introducing a solution-processed organic film between the metallic electrodes and gain media.

Controlling the electrical characteristics of Au/n‐Si structure with and without (biphenyl‐CoPc) and (OHSubs‐ZnPc) interfacial layers at room temperature

In order to interpret well whether or not the organic or polymer interfacial layer is effective on performance of the conventional Au/n‐Si (metal semiconductor [MS]) type Schottky barrier diodes (SBDs), in respect to ideality factor (n), leakage current, rectifying rate (RR), series and shunt resistances (Rs, Rsh) and surface states (Nss) at room temperature, both Au/biphenyl‐CoPc/n‐Si (MPS1) and Au/OHSubs‐ZnPc/n‐Si (MPS2) type SBDs were fabricated. The electrical characteristics of these devices have been investigated and compared by using forward and reverse bias current–voltage (I–V) characteristics in the voltage range of (−4 V)–(4 V) for with and without (biphenyl‐CoPc) and (OHSubs‐ZnPc) interfacial layers at room temperature. The main electrical parameters of these diodes such as reverse saturation current (I0), ideality factor (n), zero‐bias barrier height (ΦB0), RR, Rs and Rsh were found as 1.14 × 10−5 A, 5.8, 0.6 eV, 362, 44 Ω and 15.9 kΩ for reference sample (MS), 7.05 × 10−10 A, 3.8, 0.84 eV, 2360, 115 Ω and 270 kΩ for MPS1 and 2.16 × 10−7 A, 4.8, 0.7 eV, 3903, 62 Ω and 242 kΩ for MPS2, respectively. It is clear that all of these parameters considerably change by using an organic interfacial layer. The energy density distribution profile of Nss was found for each sample by taking into account the voltage dependence of effective barrier height (Φe) and ideality factor, and they were compared. Experimental results confirmed that the use of biphenyl‐CoPc and OHSubs‐ZnPc interfacial layer has led to an important increase in the performance of the conventional of MS type SBD. Copyright © 2015 John Wiley & Sons, Ltd.

Maximizing the value of gate capacitance in field-effect devices using an organic interface layer

Past research has confirmed the existence of negative capacitance in organics such as tris (8-Hydroxyquinoline) Aluminum (Alq3). This work explored using such an organic interface layer to enhance the channel voltage in the field-effect transistor (FET) thereby lowering the sub-threshold swing. In particular, if the values of the positive and negative gate capacitances are approximately equal, the composite negative capacitance will increase by orders of magnitude. One concern is the upper frequency limit (∼100Hz) over which negative capacitance has been observed. Nonetheless, this frequency limit can be raised to kHz when the organic layer is subjected to a DC bias.

Influence of the atmosphere on organic–organic interfacial layers and deterioration in organic light‐emitting diodes

AbstractThe influence of organic–organic interfacial contaminants and deterioration in organic light‐emitting diodes (OLEDs) was investigated. There was deterioration of the device characteristics when atmospheric contamination was introduced to the emission site. We simultaneously observed a decrease of the maximum capacitance, Cmax, of the OLEDs, implying that there was charge accumulation at the interface. Our study demonstrates that maintaining the interface adjacent to emission site free from contaminants is crucial to protect the device from deterioration.

Electrical and interfacial properties of Au/P3HT:PCBM/n-Si Schottky barrier diodes at room temperature

In this study, a gold/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/n-type silicon (Au/P3HT:PCBM/n-Si) metal-polymer-semiconductor (MPS) Schottky barrier diode (SBD) was fabricated. To accomplish this, a spin-coating system and a thermal evaporation were used for preparation of a P3HT/PCBM layer system and for deposition of metal contacts, respectively. The forward- and reverse-bias current–voltage (I–V) characteristics of the MPS SBD at room temperature were studied to investigate its main electrical parameters such as ideality factor (n), barrier height (ΦB), series resistance (Rs), shunt resistance (Rsh), and density of interface states (Nss). The I–V characteristics have nonlinear behavior due to the effect of Rs, resulting in an n value (3.09) larger than unity. Additionally, it was found that n, ΦB, Rs, Rsh, and Nss have strong correlation with the applied bias. All results suggest that the P3HT/PCBM interfacial organic layer affects the Au/P3HT:PCBM/n-Si MPS SBD, and that Rs and Nss are the main electrical parameters that affect the Au/P3HT:PCBM/n-Si MPS SBD. Furthermore, a lower Nss compared with that of other types of MPS SBDs in the literature was achieved by using the P3HT/PCBM layer. This lowering shows that high-quality electronic and optoelectronic devices may be fabricated by using the Au/P3HT:PCBM/n-Si MPS SBD.

Direct Observation of Dipole Influence Induced by a Spin Coated Organic Interfacial Layer on Effective Schottky Barrier Height Modulation of Hg/Si Contact

A thin organic interfacial layer fabricated by a spin coating method based on 80% ethoxylated polyethylenimine (PEIE) solution is demonstrated to be able to effectively modulate the Schottky barrier height (SBH) of Hg/Si contact. A 0.28 eV reduction of effective electron affinity for the PEIE coated Si is observed by Kelvin probe measurement, which directly reveals the dipole influence induced by the PEIE layer. Capacitance-voltage and current-voltage measurements further demonstrate that the SBH modulation is dominated by the interlayer dipole effect.

Interfacial Organic Layers for Chemical Stability and Crystalline Ordering of Thiophene and Carboxyl Films on a Metal Surface

Organic-based devices require multicomponent, multilayer architectures consisting of functional molecules that may be chemically unstable at a metal interface. In this work, we demonstrate that an interfacial organic layer (IOL) provides chemical stability at and above room temperature, while also achieving desired crystalline ordering of the functionalized organic layer. As the IOL decouples organic species from direct interactions with the metal, new structural motifs become available that are not otherwise observed, yielding the first submolecular resolution imaging of phenylthiophene stacking at a surface. We studied self-organized layers comprising two classes of functional groups, carboxylic acids and thiophenes, which have applications in organic electronics but are each chemically unstable and structurally disordered when deposited directly onto the Cu(001) and other metal surfaces. The IOL strategy demonstrated here resolves these issues and broadens opportunities for organic thin films on metal ...

External quantum efficiency enhancement in organic photovoltaic devices employing dual organic anode interfacial layers

We demonstrate the use of a dual anode interfacial layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and tetracene for efficient small molecule organic solar cells. These layers provided a multifaceted improvement on device performance by enhancing absorption in the donor layer, serving as an exciton blocking layer at the anode interface, providing a low resistance anode contact, and serving as a templating layer for increased crystallinity in the donor layer. Palladium phthalocyanine/C60 planar heterojunction devices fabricated on top of the dual layers of PEDOT:PSS and tetracene demonstrates 85% enhancement in the donor contribution to external quantum efficiency and yielded a maximum power conversion efficiency of 3.66%.

A detailed comparative study on the main electrical parameters of Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes

We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (ΦB0), series resistance (Rs), and shunt resistance (Rsh) with values of 1.38, 0.75eV, 97.64Ω, and 203MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62eV, 164.15Ω and 0.597MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (Nss). The values of Nss range from 1.36×1012 at Ec—0.569eV to 1.35×1013eV−1cm−2 at Ec—0.387eV for Au/PVA:Zn/n-Si SBD and 3.34×1012 at Ec—0.560eV to 1.35×1013eV−1cm−2 at Ec—0.424eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.

Fabrication of organic interfacial layers by molecular layer deposition: Present status and future opportunities

To keep pace with the miniaturization of next generation devices in applications such as electronics, biotechnology, and energy, their constituent polymer thin films must meet challenging requirements such as providing simultaneously ultrathin and conformal coatings. Traditional polymer deposition methods may not be suitable, and as a result, new fabrication methods are needed. Molecular layer deposition (MLD), as an analog to atomic layer deposition, provides precise control over many polymer film properties, such as thickness, composition, morphology, and conformality. Hence, MLD can be a powerful and novel method for fabrication of polymer films. This review article introduces the variety of polymer films that have been developed using MLD together with important film growth characteristics and properties. Examples of MLD polymer applications are provided as well. Finally, challenges and outlooks of the MLD technique are discussed.

The Effect of Organic and Metal Oxide Interfacial layers on the Performance of Inverted Organic Photovoltaics

AbstractWe study the origin of the improvement of the power conversion efficiency (PCE) of inverted organic solar cells when an interfacial insulating organic layer of polyoxyethylene tridecyl ether (PTE) is introduced between the indium tin oxide (ITO) bottom electrode and the TiOx interfacial layer. XPS and UPS measurements are used to investigate the energy level alignment at the interfaces within the ITO/TiOx and ITO/PTE/TiOx structures and to identify any effects due to chemical interaction and interfacial dipoles. Scanning electron microscopy studies show that the surface structure of the TiOx layer is affected, when it is coated on top of the PTE layer. Surface contact angle measurements show that the incorporated interfacial layer of PTE is more hydrophilic than ITO and thus PTE modified TiOx becomes more hydrophilic. This, in combination with the surface gaps of the PTE interfacial layer, is likely to lead to changed wetting and hydrolysis properties of TiOx when coated on ITO/PTE than on ITO alone. The different TiOx layer quality is reflected in improved electron selectivity, leading to enhanced fill factor, reduced parasitic resistance effects and higher power conversion efficiency for inverted solar cells with a PTE interfacial layer between ITO and TiOx.

Initial Stages of Atomic Layer Deposition of Tantalum Nitride on SiO2 and Porous Low-κ Substrates Modified by a Branched Interfacial Organic Layer: Chemisorption and the Transition to Steady-State Growth

We have examined the initial stages of atomic layer deposition (ALD) of TaNx on SiO2, a porous low-κ SiO2-based material, and both of these substrates modified by a branched interfacial organic layer, using in situ X-ray photoelectron spectroscopy (XPS) as the primary analytical method. The interfacial organic layer examined was poly(ethylene imine) (PEI), a branched molecule with amine functionality. We find that PEI alters both the density and nature of the species formed after the chemisorption of Ta[N(CH3)2]5, which represents the first half-cycle of ALD. In particular, PEI suppresses chemisorption of Ta[N(CH3)2]5 on SiO2 while enhancing it on low-κ. Results from XPS suggest that the Ta species on low-κ and both surfaces modified by PEI are formed in reduced concentrations while also retaining more N(CH3)2 ligands. From angle-resolved XPS, PEI acts as an effective barrier to Ta penetration of porous low-κ, even for exposures to Ta[N(CH3)2]5 at many mTorr of partial pressure. Concerning ALD, growth on ...

Solution processed small molecule organic interfacial layers for low dark current polymer photodiodes

We demonstrate a small molecule solution processed hole interfacial layer approach to improve the dark current characteristics of polymer photodiodes. The two hole blocking materials under investigation 3-phenyl-4(1′-naphthyl)-5-phenyl-1,2,4-triazole (TAZ) and 2-[3,5-bis(1-phenylbenzimidazol-2-yl)phenyl]-1-phenylbenzimidazole (TPBi) are spincoated from ethanol as an orthogonal solvent on top of a P3HT:PCBM active layer. We reduce the dark current at a bias voltage of −1V by a factor of 17.2 by introducing a TAZ interfacial layer while keeping the responsivity unchanged.

Electrical and photocurrent characteristics of Au/PVA (Co-doped)/n-Si photoconductive diodes

Abstract In this work, we investigate the some main electrical and photocurrent properties of the Au/PVA(Co-doped)/n-Si diodes by using current–voltage (I–V) measurements at dark and various illumination intensity. Two types of diodes with and without polyvinyl alcohol (PVA) (Co-doped) polymeric interfacial layer were fabricated and measured at room temperature. Results show that the polymeric interfacial layers and series resistance (Rs) strongly affect the main electrical parameters of these structures. Also, metal/polymer/semiconductor (MPS) diode with PVA (Co-doped) interfacial organic layer is very sensitive to the light such that the current in reverse bias region increase by 103–104 times with the increasing illumination intensity. The open circuit voltage Voc and short-circuit current Isc values of this MPS diode under 100 mW/cm2 illumination intensity were found as 0.28 V and 19.3 μA, respectively.

Influence of Interface Layers on Ag Thin Film Growth

We prepared Ag thin films on SiO2/Si substrates, with and without a subnanometer-thick organic interface layer of 3-mercaptopropyltrimethoxysilane (MPTMS). The surface morphology and electrical resistivity of these films were investigated and compared. Ag films grown with an MPTMS layer were relatively flat, resulting in a smaller critical thickness. This was probably because migration of Ag atoms on the substrate was suppressed by interactions between the Ag atoms and the thiol moiety. The deposition rate and terminating group of the organic interface layer also influenced the Ag film growth.

Electrical properties and barrier modification of GaAs MIS Schottky device based on MEH-PPV organic interfacial layer

We report fabrication and electrical characterization of GaAs based metal-interfacial layer-semiconductor (MIS) device with poly[2-methoxy-5-(2/-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), as an interfacial layer. MEH-PPV raises the barrier height in Al/MEH-PPV/p-GaAs MIS device as high as to 0.87eV. A Capacitance-Voltage (C–V) characteristic exhibits a low hysteresis voltage with an interface states density of 1.69×1011cm−2eV−1. Moreover, a high transition frequency (fc) of about 50kHz was observed in the accumulation mode. The photovoltaic response of Al/MEH-PPV/p-GaAs device was measured under the air masses (AM) 1.0 and 1.5. The open circuit voltage (VOC), short circuit current (ISC), fill factor and the efficiency of the Al/MEH-PPV/p-GaAs device were found to be 1.10V, 0.52mA, 0.65, and 5.92%, respectively, under AM 1.0 condition.

High barrier Schottky diode with organic interlayer

A new Cu/n-InP Schottky junction with organic dye (PSP) interlayer has been formed by using a solution cast process. An effective barrier height as high as 0.82 eV has been achieved for Cu/PSP/n-InP Schottky diodes, which have good current–voltage (I–V) characteristics. This good performance is attributed to the effect of formation of interfacial organic thin layer between Cu and n-InP. By using capacitance–voltage measurement of the Cu/PSP/n-InP Schottky diode the diffusion potential and the barrier height have been calculated as 0.73 V and 0.86 eV, respectively. From the I–V measurement of the diode under illumination, short circuit current (Isc) and open circuit voltage (Voc) have been extracted as 0.33 μA and 150 mV, respectively.

Cross-Linked Perylene Diimide-Based n-Type Interfacial Layer for Inverted Organic Photovoltaic Devices

This contribution describes the synthesis and characterization of a perylene diimide (PDI)-based n-type semiconductor and its application to organic photovoltaic (OPV) devices having inverted architecture. Films of N,N'-bis(3-trimethoxysilylpropyl)-1,6,7,12-tetrachloroperylene-3,4,9,10-tetracarboxyldiimide (Cl(4)PSi(2)) and blends of this material with various polymers are solution-deposited on tin-doped indium oxide (ITO) substrates as interfacial layers (IFLs). The organic IFL described in this work is based on the air- and light-stable PDI core, annealed at low temperatures compatible with flexible substrates, and crosslinks in air for compatibility with device fabrication. Morphological, optical, and electrochemical analysis of these IFL films demonstrate predominantly smooth surfaces and HOMO and LUMO energies of ~4.5 and 7.0 eV, respectively, which are ideal for accepting electrons and blocking holes in inverted devices. A cationic silane species is added to the Cl(4)PSi(2) at an optimum ~2-5 wt % to reduce IFL series resistance and enhance device performance. Also, a short light soaking procedure is necessary for completed devices to achieve high fill factors in current density-voltage analysis, a phenomenon previously only observed for inverted devices having an n-type inorganic IFL.

Electronic parameters of high barrier Au/Rhodamine-101/ n-Inp Schottky diode with organic ınterlayer

In this work, we present that Rhodamine-101 (Rh-101) organic molecules can control the electrical characteristics of conventional Au/ n-InP metal–semiconductor contacts. An Au/ n-InP Schottky junction with Rh-101 interlayer has been formed by using a simple cast process. A potential barrier height as high as 0.88 eV has been achieved for Au/Rh-101/ n-InP Schottky diodes, which have good current–voltage (I–V) characteristics. This good performance is attributed to the effect of formation of interfacial organic thin layer between Au and n-InP. By using capacitance-voltage measurement of the Au/Rh-101/ n-InP Schottky diode the diffusion potential and the barrier height have been calculated as 0.78 V and 0.88 eV, respectively. From the I–V measurement of the diode under illumination, short circuit current and open circuit voltage have been extracted as 1.70 μA and 240 mV, respectively.