Modified Indium Tin Oxide Anodes Research Articles

Gold nanoparticals modified indium tin oxide anode for high performance red perovskite light emitting diodes

Gold nanoparticles (Au NPs) play an important role in improving the external quantum efficiency of perovskite light emitting diodes (PeLED). To avoid direct contact between the Au NPs and the light emitting layer, the Au NPs@SiO<sub>2</sub> structure and blending the Au NPs into the hole transport layer (HTL) or electron transport layer (ETL) have been proposed previously. However, the Au NPs@SiO<sub>2</sub> is difficult to obtain and affects the charge transport. When the Au NPs is blended in poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS), the density of Au NPs is not easily controlled and the PEDOT:PSS is not an ideal HTL for PeLED. Therefore, the electrostatic adsorption is used in this work to uniformly disperse the ~20 nm-size Au NPs on the top of the ITO anode, and the Poly(9-vinylcarbazole) (PVK) is spin-coated as the HTL to achieve the high performance red PeLED based on the (NMA)<sub>2</sub>Cs<sub><i>n</i>–1</sub>Pb<sub><i>n</i></sub>I<sub>3<i>n</i>+1</sub>. After the Au NPs modification, the maximum luminous brightness rises from ~5.2 to ~83.2 cd/m<sup>2</sup>. Meanwhile, the maximum external quantum efficiency rises from ~0.255% to ~6.98%. Mechanism studies show that microcavity can be formed between the Au NPs-modified ITO anode and the Al cathode, and the transmitted light and the reflected light interfere with each other to improve the output couple efficiency of the PeLED. The photoluminescence (PL) spectrum and angle dependent PL intensity of the Au NPs-modified PeLED prove that the fluorescence enhancement of the (NMA)<sub>2</sub>Cs<sub><i>n</i>–1</sub>Pb<sub><i>n</i></sub>I<sub>3<i>n</i>+1</sub> perovskite is attributed mainly to the microcavity effect. Furthermore, the effects of Au NPs density on the performance of the PeLED are investigated, which reveals that the device with ~15 min adsorption is optimal. Finally, we rule out the contributions of Au NPs to the morphology, crystallization, electrical properties and localized surface plasmon resonance (LSPR) effects of (NMA)<sub>2</sub>Cs<sub><i>n</i>–1</sub>Pb<sub><i>n</i></sub>I<sub>3<i>n</i>+1</sub> perovskite films. In this work, the Au NPs are successfully applied to red PeLED for the first time, providing a feasible way of developing the low-cost and high-efficiency PeLED.

Effects of organic acids modified ITO anodes on luminescent properties and stability of OLED devices

In this paper, p-chlorophenylacetic acid and p-fluorophenylacetic acid were applied to modify the indium tin oxide (ITO) electrodes. The surface work functions of unmodified ITO, p-chlorophenylacetic acid modified ITO (Cl-ITO) and p-fluorophenylacetic acid modified ITO (F-ITO) are 5.0 eV, 5.26 eV and 5.14 eV, respectively, and the water contact angles are 7.3°, 59.1° and 46.5°, respectively. The increase of the work function makes the hole injection ability of the devices improved, which is proved by the hole transport devices. The self-assembly (SAM) layers transfer hydrophilic ITO to hydrophobic ITO, which makes ITO more compatible with the hydrophobic organic layers, making the organic film more stable during the operation. After modification, the organic light emitting diodes (OLEDs), SAM-modified ITO/NPB/Alq3/LiF/Al, with better performance and stability were fabricated. Especially, the OLED with Cl-ITO (Cl-OLED) has a maximum luminance of 22 428 cd/m2 (improved by 32.9%) and a half-lifetime of 46 h. Our results suggest that employing organic acids to modify ITO surface can enhance the stability and the luminescent properties of OLED devices.

Performance enhancement of polymer solar cells with high work function CuS modified ITO as anodes

In this paper, a thin layer of high work function CuS was introduced to the interface between the anode and hole transporting layer (HTL) to modify the indium tin oxide (ITO) anode. Modified ITO substrates possess a higher work function, a lower sheet resistance and a negligible loss in transparency. More importantly, a thin layer of CuS can also benefit for the hole transporting of the device. Polymer solar cells (PSCs) utilizing modified ITO anodes exhibit a significant enhancement in power conversion efficiency (PCE) and air stability compared to devices with normal ITO anodes. This anode modification strategy applies to different active layer systems. Anode-modified devices with poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the active layer exhibit a PCE of 3.5%, while poly(4,8-bis(5-(2-ethyl-hexyl)-thiophene-2-yl)-benzo[l,2-b:4,5-b′] dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene) (PBDTTT-C-T) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) system shows a PCE of 7.4%. As a result, this work provides a good compatibility for modification of ITO by a thin layer of CuS in PSCs to achieve better performance.

High performance semitransparent phosphorescent white organic light emitting diodes with bi-directional and symmetrical illumination

A semitransparent white organic light-emitting diode (WOLED) is produced based on a blue phosphorescence from iridium(III)[bis(4,6-difuorophenyl)-pyridinato-N,C2] picolinate and an orange phosphorescence from bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3) iridium(acetylacetonate). In this work, a hole-transporting layer of N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (NPB) and an electron-transporting layer of 3,5,3″,5″-tetra-3-pyridyl-[1,1′;3′,1″] terphenyl (B3PyPB) were used. B3PyPB has high electron mobility and a high triplet energy level. The use of B3PyPB helps to reduce the triplet quenching and also to confine the charge recombination in the emissive region of a single-host two-color WOLED. A bi-layer Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and a cathode of Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) were employed. The semitransparent WOLEDs thus developed have perfect symmetrical, bi-directional illumination characteristics, and the weak angular dependent EL emission spectra, which are beneficial for application in planar diffused lighting.

Gold nanoparticles modified ITO anode for enhanced PLEDs brightness and efficiency

We reported a facile and controllable electrostatic adsorption of gold nanoparticles (Au NPs) on an indium tin oxide (ITO) anode, for applications in polymer light-emitting diodes (PLEDs). Au NPs (size 20 nm) were found to be well dispersed on a pre-treated ITO anode, and the density of Au NPs was well controlled from 0 to 60 μm−2 depending on the adsorption time. By using the Au NPs modified ITO as the anode, the optimized PLEDs showed a 60% enhancement in brightness and 40% enhancement in luminous efficiency. Our results showed that the enhancement of devices performance mainly originated from enhanced photoluminescence, the maximum of luminous efficiency appeared when the distance of Au NPs and light emission profile was about 40–80 nm, which indicated that the origin of enhanced luminescence is due to the “far-field” effect of the Au NPs layer rather than a classical localized surface plasma resonance.

Platinum nanoparticles modified indium tin oxide anodes for enhancing the efficiency and stability of organic solar cells

Organic P3HT:PCBM heterojunction solar cells with indium tin oxide (ITO) anodes modified by platinum nanoparticles (NPs) were fabricated. The open-circuit voltage (Voc) of the cells was increased compared with the reference cell without Pt NPs. An enhanced power conversion efficiency of ∼12% was obtained for the optimum sputtering deposition duration of 10s. A double junction model of the Schottky junction and the p–n junction is proposed to describe the frequency dependence of the capacitance in the modified cell. The formation of the front Schottky junction allows efficient collection of holes from the active layer, and enhances the Voc. Moreover, the air stability of organic solar cells was improved. The modification of ITO with Pt NPs shows promise as a technique for fabrication of high-efficiency stable photovoltaic devices.

Band Alignment at Anode/Organic Interfaces for Highly Efficient Simplified Blue-Emitting Organic Light-Emitting Diodes

Efficient simplified blue-emitting phosphorescent organic light-emitting diodes (OLEDs) were fabricated with a nickel oxide (Ni2O3) or molybdenum oxide (MoO3) modified indium tin oxide (ITO) anode. The maximum current efficiency of device anode/bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium (FIrpic)/FIrpic:1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi)/LiF/Al was increased from 3.6 cd/A with ITO anode to 22.0 and 23.6 cd/A for Ni2O3 and MoO3 modified ITO anodes, respectively. Moreover, the maximum current and power efficiencies of another bilayer device ITO/MoO3/FIrpic:4,4′-N,N′-dicarbazole-biphenyl (CBP)/FIrpic:TPBi/LiF/Al were as high as 49 cd/A and 48 lm/W, respectively. Photoelectron spectroscopy measurements were employed to investigate the electronic structure of the anode/organic interfaces. Results show that the band alignment at the oxide/organic interface plays a critical role in these simplified blue devices.

4.8% efficient poly(3-hexylthiophene)-fullerene derivative (1:0.8) bulk heterojunction photovoltaic devices with plasma treated AgOx/indium tin oxide anode modification

We report here an improved efficiency, up to 4.8% with a high fill factor of ∼63% under AM 1.5G spectral illumination and 100mW∕cm2 intensity, for poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction photovoltaic (PV) devices with a 1:0.8 weight ratio using surface modifications to the indium tin oxide (ITO) anodes through plasma oxidized silver. Here, an enhanced short-circuit current density was achieved without significant loss in the open-circuit voltage (>0.6V) nor the fill factor (>63%), leading to an efficiency jump from 4.4% in the control devices to 4.8% with the surface modified ITO anode. The enhanced short-circuit density is attributed to an interface energy step between the ITO and the polymer hole transporting layer. It has been theorized that the introduction of an interface energy step could alter the charge collection efficiency, resulting in an improved overall efficiency in PV devices. In our study, the current density–voltage characteristics under darkness clearly show an increased current density, especially under forward bias, for the anode treated cell, suggesting the presence of an interface energy step between the ITO and the hole transporting layer with surface modified ITO anodes.

Current-voltage behavior in hole-only single-carrier devices with self-assembling dipole molecules on indium tin oxide anodes

The authors report the use of chemically modified indium tin oxide (ITO) with different binding groups (–COCl and –PO2Cl2) of p-chlorobenzene derivatives forming effective monolayers to control the work function of ITO and hence to enhance the hole injection. The enhanced hole injection is studied by measuring current density–voltage (J-V) characteristics. The behavior of J-V characteristics caused by varying the ITO work function in hole-only single-carrier devices with a hole transport layer of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine is examined. Upon grafting with p-chlorophenylphosphoryl dichloride, the J-V characteristics show a space-charge-limited conduction behavior. Such modified ITO anodes lead to improvements in the device properties.

Molecular-scale interface engineering for polymer light-emitting diodes

Achieving balanced electron-hole injection and perfect recombination of the charge carriers is central to the design of efficient polymer light-emitting diodes (LEDs). A number of approaches have focused on modification of the injection contacts, for example by incorporating an additional conducting-polymer layer at the indium-tin oxide (ITO) anode. Recently, the layer-by-layer polyelectrolyte deposition route has been developed for the fabrication of ultrathin polymer layers. Using this route, we previously incorporated ultrathin (<100 A) charge-injection interfacial layers in polymer LEDs. Here we show how molecular-scale engineering of these interlayers to form stepped and graded electronic profiles can lead to remarkably efficient single-layer polymer LEDs. These devices exhibit nearly balanced injection, near-perfect recombination, and greatly reduced pre-turn-on leakage currents. A green-emitting LED comprising a poly(p-phenylene vinylene) derivative sandwiched between a calcium cathode and the modified ITO anode yields an external forward efficiency of 6.0 per cent (estimated internal efficiency, 15-20 per cent) at a luminance of 1,600 candelas per m2 at 5 V.