MoO3/Au/MoO3–PEDOT:PSS multilayer electrodes for ITO-free organic solar cells

The effect of the MoO₃–PEDOT:PSS composite layer in the MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrode on the power conversion efficiency of ITO-free organic solar cells (OSCs) was evaluated. The MoO₃ (30 nm)/Au(12 nm)/MoO₃–PEDOT:PSS (30 nm)/PEDOT:PSS structure showed ~7% more optical transmittance than the MoO₃ (30 nm)/Au (12 nm)/MoO₃(30 nm)/PEDOT:PSS structure at 550 nm wavelength. The OSCs using MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrodes as anodes showed a considerable improvement in power conversion efficiency (PCE), from 1.84% to 2.81%, comparable to ITO based OSCs with PCE of 2.89%. This improvement is attributed to the suppression of MoO₃ dissolution by the acidic hole transport layer (HTL) PEDOT:PSS on the MoO₃/Au/MoO₃–PEDOT:PSS multilayer electrode, resulting in high J_sc, V_oc and FF of the OSCs. This composite based multilayer electrode was shown to be a promising replacement in ITO-free flexible optoelectronic devices.     

Flexible inverted polymer solar cells on polyethylene terephthalate substrate containing zinc oxide electron-collection-layer prepared by novel sol–gel method and low-temperature treatments

Flexible and air-stable polymer solar cells were fabricated on a polyethylene terephthalate (PET) substrate. The cell structure was indium tin oxide (ITO) on PET/zinc oxide (ZnO)/[6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM):regioregular poly(3-hexylthiophene) (P3HT)/poly (3,4-ethylenedioxylenethiophene):poly(4-styrene sulfonic acid) (PEDOT:PSS)/Au, this being called the ZnO cell. Reproducible cell performances were obtained despite the ZnO cells being fabricated in air and at low temperature, using a novel ZnO precursor solution containing zinc(II) acetylacetonate as a metal source and acetylacetone as a Zn²⁺ complexing agent. The power conversion efficiency (PCE) of the flexible ZnO cells without sealing was 2.15% under irradiating AM1.5G simulated sunlight at 100 mW cm^?2. In addition, the performance of the non-sealed ZnO cells was almost constant in ambient atmosphere under continuous light irradiation for 100 h.     

Improvement of electrical conductivity of PEDOT:PSS films by 2-Methylimidazole post treatment

The electrical conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films was significantly improved without losing the optical transparency by treating the films with solution of 2-Methylimidazole in ethanol. The maximum electrical conductivity of such a thin film reached 930 S cm⁻¹, more than 1150 order of magnitude higher than that of pure PEDOT:PSS film. The mechanism of conductivity enhancement of treated thin PEDOT:PSS films was explored by atomic force microscopy (AFM) and UV/VIS spectrophotometer. The AFM scans show that the surface of the 2-Methylimidazole treated PEDOT:PSS layer is smoother than that of the pristine PEDOT:PSS thin film. Improvement in the morphology, electrical and optical properties of PEDOT:PSS films makes them highly suitable for numerous applications in optoelectronic devices.     

Influence of aluminium electrode preparation on PCE values of polymeric solar cells based on P3HT and PCBM

The main goal of the paper was investigation of influence of aluminum electrode preparation via thermal evaporation (TE) and the magnetron sputtering (MS) on power conversion efficiency (PCE) of polymeric solar cells. The photovoltaic properties of such three kinds devices based on poly(3-hexylthiophene-2,5-diyl) (P3HT) as ITO/P3HT/Al, ITO/P3HT:PCBM (1:1, w/w)/Al and ITO/PEDOT:PSS/P3HT:PCBM (1:1, w/w)/Al were investigated. For the constructed devices impedance spectroscopy were analyzed. For devices lack of PEDOT:PSS layer or lack of PCBM, photovoltaic parameters were very low and similar to the parameters obtained for device with Al electrode prepared by magnetron sputtering. The devices comprising PEDOT:PSS with P3HT:PCBM showed the best photovoltaic parameters such as a V_OC of 0.60 V, J_SC of 4.61 mA/cm², FF of 0.21, and PCE of 5.7 × 10^?1%.     

An inverted,organic WORM device based on PEDOT:PSS with very low turn-on voltage

An organic Write-Once-Read-Many (WORM) device based on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as the active layer was fabricated with an inverted architecture. Insertion of an ultrathin layer of poly(methylmethacrylate) (PMMA) between the bottom electrode and the PEDOT:PSS resulted in a systematic and substantial decrease in turn-on voltage, from 7.0 V to less than 1.0 V. An optimal thickness of the PMMA layer was found to yield the lowest consistent turn-on voltage of ∼0.8 V, with 0.5 V being the lowest value of all fabricated devices. The switching mechanism was attributed to filamentary doping of the PEDOT:PSS. Insertion of the PMMA acted to protect the underlying ZnO from being etched by the acidic PEDOT:PSS as well as to improve its wetting properties. Devices were demonstrated on both ITO and aluminum bottom electrodes, with aluminum yielding the highest ON/OFF ratios in the study. Owing to their inverted architecture, the devices demonstrated good stability, and the retention time of the ON-state was determined to be greater than twenty months while stored in air for devices with ITO bottom electrodes. In addition to deposition via spin-coating, blade-coating was demonstrated as a viable processing technique for applications requiring rapid or large-area manufacturing.     

Investigations on the annealing behavior of high-energy carbon irradiated Au/n-GaAs Schottky barrier diodes

Au Schottky barrier diodes (SBDs) have been irradiated using high-energy carbon ion fluences of 1×10¹¹, 1×10¹² and 1×10¹³ cm⁻². Current–voltage characteristics of unirradiated and irradiated diodes have been analyzed. The change in reverse leakage current increases with increasing ion fluence due to the irradiation-induced defects at the interface. The diodes were annealed at 523 and 623 K to study the effect of annealing. The rectifying behavior of the irradiated SBDs improves at 523 K. But at 623 K, the diode behavior deteriorates irrespective of the fluences. Better enhancement in the barrier height and also improvement in the ideality factor of the diodes has been observed at the annealing temperature of 523 K. Scanning Electron Microscopic analysis was carried out on the irradiated samples to delineate the projected range of the defects by high-energy carbon ion irradiation.     

Effects of UV light-irradiated buffer layer on the performance of polymer solar cells

We investigate the effect of a UV-irradiated poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the performance of polymer photovoltaic cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends. It was found that UV irradiation can reduce the bulk and contact resistance of PEDOT:PSS films, improving the power conversion efficiency from (3.05 ± 0.04)% to (3.50 ± 0.03)% due to the lower device series resistance under an illumination of AM1.5G, 100 mW/cm². The work function change after UV irradiation and negligible surface morphology change was noticed.     

Alcohol-soluble polyfluorenes containing dibenzothiophene-S,S-dioxide segments for cathode interfacial layer in PLEDs and PSCs

A series of alcohol-soluble amino-functionalized polyfluorene derivatives (PF-N-S, PF-N-SC8 and PF-N-SOC8) comprising various ratios of dibenzothiophene-S,S-dioxide segments (S/SC8/SOC8) in the main chains, respectively, were synthesized and utilized as cathode interfacial layer (CIL) in polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) with high-work-function Al (or Au) electrode. The polymers possess LUMO/HOMO levels at −2.78 to −3.53 eV/−5.69 to −6.32 eV. Multilayer PLEDs and PSCs with device configurations of ITO/PEDOT:PSS (40 nm)/P-PPV or PFO-DBT35:PCBM = 1:2 (80 nm)/CIL (3–15 nm)/Al (or Au) (100 nm) were fabricated. The PF-N-S-10/Al (or Au) cathode PLEDs displayed maximum luminous efficiency of 24.4 cd A⁻¹ (or 11.9 cd A⁻¹), significantly higher than bare Al (or Au) cathode device, exceeding well-known Ba/Al and poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN)/Al (or PFN/Au) cathode devices. The enhanced open-circuit voltages (V_ocs), electron reflux and reduced work functions clarify that the electron injection barrier from the Al (or Au) electrode can be lowered by inserting the polymers as CIL. The resulted PSCs also show device performances exceeding Al and PFN/Al cathode devices. The results indicate that PF-N-S, PF-N-SC8 and PF-N-SOC8 are excellent CIL materials for PLEDs and PSCs with high-work-function Al or Au electrode.     

Flexible,plastic transistor-based chemical sensors

Flexible, plastic chemical sensors were fabricated using a thin polymer gate dielectric layer and polymer electrodes patterned via selective wetting directly on the surface of the organic semiconductor film. Low-voltage transistors based on DDFTTF with PEDOT:PSS electrodes had a mobility as high as 0.05 cm²/Vs with an on–off ratio of 1.2 × 10⁴ on ITO/PET substrates. These devices demonstrated stable operation in water with sensor characteristics similar to those reported on rigid silicon substrates, with sub-ppm detection for cysteine and 2,4,6-trinitrobenzene (TNB).     

New wide-bandgap organic donor and its application in UVB sensors with high responsivity

A triarylamine-containing fluorene derivative (FP) with wide bandgap and excellent thermal stability was synthesized and used as electron donor to construct planar heterojunction organic ultraviolet sensor (UVS), while bis(4-(4,6-diphenyl-1,3,5-triazine-2-yl)phenyl)diphenylsilane (NSN) was used as electron acceptor. The UVS ITO/PEDOT:PSS/FP/NSN/LiF/Al showed sensitive visible-blind response to UV illumination from both ITO and cathode sides. When no bias applied, the peak responsivity to UV light through ITO and cathode side was 47 and 33 mA/W, respectively. To the irradiation from the semitransparent Al side, the most sensitive response range covers the UVB region. Under a bias of ?4 V, the peak responsivity at 300 nm reaches 473 mA/W.     

The enhancement of electrical and optical properties of PEDOT:PSS using one-step dynamic etching for flexible application

The conductivity enhancement of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by dynamic etching process was investigated to introduce the outstanding and simplest method for soft electronics. Four different samples which were pristine PEDOT:PSS, PEDOT:PSS doped with 5 wt.% DMSO, PEDOT:PSS with dipping process, and PEDOT:PSS with dynamic etching process were prepared to compare the properties such as conductivity, morphology, relative atomic percentage, and topography. All samples were characterized by four point probe, current atomic force microscopy (C-AFM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. The conductivity of the sample with dynamic etching process showed the highest value as 1299 S/cm among four samples. We proved that the dynamic etching process is superior to remove PSS phase from PEDOT:PSS film, to flow strong current through entire surface of PEDOT:PSS, and to show the smoothest surface (RMS 2.28 nm). XPS analysis was conducted for accurate chemical and structural surface environments of four samples and the relative atomic percentage of PEDOT in the sample with dynamic etching was the highest as 29.5%. The device performance of the sample with the dynamic etching process was outstanding as 10.31 mA/cm² of J_sc, 0.75 eV of V_oc, 0.46 of FF, and 3.53% of PCE. All properties and the device performance for PEDOT:PSS film by dynamic etching process were the most excellent among the samples.     

Indium zinc oxide ohmic contact to poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) induced by UV light

In this research, we investigated the I–V characteristics of ITO/PEDOT:PSS/InZnO devices for two sets of samples. The first set is composed of PEDOT:PSS as-prepared, while the second set is composed of PEDOT:PSS irradiated by UV light source. We found that UV irradiation improves the electrical conductivity of the fabricated devices and yields to ohmic contact. Based on the UPS measurements, it was found that UV irradiation leads to an increase in the work function and the enhancement of electrical conductivity of PEDOT:PSS films. XPS and AFM measurements indicate that conformational changes of the PEDOT:PSS films are responsible for this behavior. We also studied the effect of storage on the electrical properties of our devices. No significant changes of electrical characteristics have been found after storing the devices for a period of 30 days.     

Pt–free counter electrodes based on modified screen–printed PEDOT:PSS catalytic layers for dye–sensitized solar cells

One of the most highlighted advantages of dye-sensitized solar cells (DSSCs) consists in the possibility to apply simple and low-cost printing techniques and solution processable materials for their assembling. Here, we report on screen-printed Pt–free counter electrodes (CEs) based on poly(3,4–ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersions with different content of rheological agent – hydroxyethyl cellulose (HEC). These PEDOT:PSS dispersions, having measured pseudoplastic and thixotropic rheological behaviour, were screen–printed onto FTO glasses. The content of rheological agent in PEDOT:PSS catalytic layers showed an effect on measured thickness, electrochemical properties, specific conductivity and subsequently on the evaluated photovoltaic performance of DSSCs. The PEDOT:PSS CE with the 0.03 wt% of HEC achieved the best electrochemical performance and specific conductivity (80 S cm⁻¹), the lowest thickness of 200 nm and transparency in VIS light spectrum over 60%. DSSCs based on this PEDOT:PSS CE reached the highest conversion efficiency of 4.2% which is only approximately 40% lower value than η=6.9% evaluated for Pt CE.     

Formation of low-resistance and transparent indium tin oxide ohmic contact for high-brightness GaN-based light-emitting diodes using a Sn–Ag interlayer

We report on the formation of low-resistance and highly transparent indium tin oxide (ITO) ohmic contacts to p-GaN using a Sn–Ag alloy interlayer. Although the as-deposited Sn–Ag(6 nm)/ITO(200 nm) contacts show non-ohmic behaviors, the scheme becomes ohmic with specific contact resistance of 4.72×10⁻⁴ Ω cm² and produce transmittance of ∼91% at wavelength of 460 nm when annealed at 530 °C. Blue light-emitting diodes (LEDs) fabricated with the Sn–Ag/ITO contacts give forward-bias voltage of 3.31 V at injection current of 20 mA. LEDs with the Sn–Ag/ITO contacts show the improvement of the output power by 62% (at 20 mA) compared with LEDs with Ni/Au contacts.     

Low temperature Solution-Processed ZnO film on flexible substrate

Transparent conductive ZnO films were directly deposited on unseeded polyethersulfone (PES) substrates with a spin-spray method using aqueous solution at a low substrate temperature of 85 °C. All ZnO films were crystalline with wurtzite hexagonal structure and impurity phases were not detected. ZnO films deposited without citrate ions in the reaction solution had a rod array structure. In contrast, ZnO films deposited with citrate ions in the reaction solution had a continuous, dense structure. The transmittance of the ZnO films was improved from 11.9% to 85.3% as their structure changed from rod-like to continuous. After UV irradiation, the ZnO films with a continuous, dense structure had a low resistivity of 9.1×10⁻³ Ω cm, high carrier concentration of 2.7×10²⁰ cm⁻³ and mobility of 2.5 cm² V⁻¹ s⁻¹.     

A highly conductive PEDOT:PSS film with the dipping treatment by hydroiodic acid as anode for organic light emitting diode

A highly conductive, transparent and uniform poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) film has been developed by dipping treatment with hydriodic acid (HI) solution. The HI-treated PEDOT:PSS film can reach a sheet resistance of 68 Ω per square and a transmittance of 87% at 550 nm. The conductivity enhancement for the HI-treated film is ascribed to the permeation of proton and iodine anion of HI into PEDOT:PSS film, resulting in the separation of PSS and PEDOT chains. The phase separation of PSS and PEDOT can provide more conductive pathways for carriers to improve conductivity of the film. Using the optimized HI-treated PEDOT:PSS film as anode, we have fabricated indium tin oxide (ITO)-free organic light emitting diode (OLED), which shows better performance than the device with ITO as anode. This proves that such PEDOT:PSS film with the dipping treatment by HI solution is a promising alternative to ITO for low cost, transparent and flexible OLED application.     

Effects of tetramethylene sulfone solvent additives on conductivity of PEDOT:PSS film and performance of polymer photovoltaic cells

A solvent additive in PEDOT:PSS solution is one of many methods to improve the conductivity of the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. We explore a new type of the solvent additive, namely tetramethylene sulfone (TMS), for the fabrication of the PEDOT:PSS conductive layer in the ITO/PEDOT:PSS/P3HT:PCBM/TiO_x/Al polymer photovoltaic cells, in comparison to a more common dimethyl sulfoxide (DMSO) solvent additive. At optimal conditions, the TMS additive at 10 wt.% has been found to enhance the conductivity of pristine PEDOT:PSS films from 0.04 S/cm up to approximately 189 S/cm, compared with the highest conductivity for the case of the DMSO additive at 15 wt.% of 117 S/cm. Possible mechanisms of this conductivity enhancement, relating to the polymer conformation and the film morphology, have been investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy. The performance of the polymer photovoltaic cells fabricated with the solvent additives PEDOT:PSS films follows a similar trend to the conductivity of the films as a function of the additive concentration. The additives mainly lead to greater short circuit current density (J_sc) of the photovoltaic cells. The highest power conversion efficiency (PCE) of 2.24% of the device has been obtained with the 10 wt.% TMS additive of, compared to the PCE of 1.48% for the standard device without solvent additive.     

Effect of PEDOT–PSS resistivity and work function on PLED performance

The effect of a commonly used hole injection layer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT–PSS), on polymer light-emitting diode (PLED) performance has been investigated. A series of four different types of commercial PEDOT–PSS, with varying resistivity and work function were examined in devices with the structure Indium Tin Oxide (ITO)/PEDOT–PSS/High Molecular Weight Poly(n-vinylcarbazole) (PVKH): 30% N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD)/Low molecular Weight Poly(n-vinylcarbazole) (PVKL): 40% 2-(4-Biphenyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole (PBD): 8% Ir(ppy)₃. It was found that the PEDOT–PSS with the highest work function and resistivity produced the devices with the highest efficiencies; this is due to the improved hole injection effect, the decrease in electron leakage current and the prevention of pixel crosstalk. A maximum device current efficiency of 33.4 cd A⁻¹ has been achieved for the most resistive PEDOT; this corresponded to an external quantum efficiency (E.Q.E.) of 11%. Increasing the work function of the PEDOT used resulted in a 60% increase in E.Q.E. and device efficiency for PEDOTs in the same resistivity range. Drift–diffusion simulations, carried out using SEmiconducting Thin Film Optics Simulation software (SETFOS) 3.2, produced J–V curves in good agreement with the experimentally observed results; this allowed us to extract qualitative values for the effective device mobility along with the PEDOT work function and resistivity.     

Metal salt modified PEDOT:PSS as anode buffer layer and its effect on power conversion efficiency of organic solar cells

The effects of metal chlorides such as LiCl, NaCl, CdCl₂ and CuCl₂ on optical transmittance, electrical conductivity as well as morphology of PEDOT:PSS films have been investigated. Transmittance spectra of spun PEDOT:PSS layers were improved by more than 6% to a maximum of 94% in LiCl doped PEDOT:PSS film. The surface of the PEDOT:PSS films has exhibited higher roughness associated with an increase in the electrical conductivity after doping with metal salts. The improvement in the physical properties of PEDOT:PSS as the hole transport layer proved to be key factors towards enhancing the P3HT:PCBM bulk heterojunction (BHJ) solar cells. These improvements include significantly improved power conversion efficiency with values as high as 6.82% associated with high fill factor (61%) and larger short circuit current density (∼18 mA cm⁻²).     

Investigation of structural and optoelectronic properties of annealed nickel phthalocyanine thin films

Thin films of nickel phthalocyanine (NiPc) were prepared by thermal evaporation and the effects of annealing temperature on the structural and optical properties of the samples were studied using different analytical methods. Structural analysis showed that the grain size and crystallinity of NiPc films improved as annealing temperature increased from 25 to 150 °C. Also, maximum grain size (71.3 nm) was obtained at 150 °C annealing temperature. In addition, NiPc films annealed at 150 °C had a very smooth surface with an RMS roughness of 0.41 nm. Optical analysis indicated that band gap energy of films at different annealing temperatures varied in the range of 3.22–3.28 eV. Schottky diode solar cells with a structure of ITO/PEDOT:PSS/NiPc/Al were fabricated. Measurement of the dark current density–voltage (J–V) characteristics of diodes showed that the current density of films annealed at 150 °C for a given bias was greater than that of other films. Furthermore, the films revealed the highest rectification ratio (23.1) and lowest barrier height (0.84 eV) demonstrating, respectively, 23% and 11% increase compared with those of the deposited NiPc films. Meanwhile, photoconversion behavior of films annealed at 150 °C under illumination showed the highest short circuit current density (0.070 mA/cm²) and open circuit voltage of (0.55 V).