All‐Solution‐Processed Pure Formamidinium‐Based Perovskite Light‐Emitting Diodes

All‐solution‐processed pure formamidinium‐based perovskite light‐emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr₃ device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution‐processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution‐processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W^?1, a peak current efficiency of 21.3 cd A^?1, and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 10⁵ cd m^?2. A record lifetime T₅₀ of 436 s is achieved at the initial brightness of 10 000 cd m^?2. Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn‐on voltage is attributed to Auger‐assisted energy up‐conversion process.     

An Efficiently Doped PEDOT:PSS Ink Formulation via Metastable Liquid−Liquid Contact for Capillary Flow-Driven,Hierarchically and Highly Conductive Films

With commercial electronics transitioning toward flexible devices, there is a growing demand for high-performance polymers such as poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS). Previous breakthroughs in promoting the conductivity of PEDOT:PSS, which mainly stem from solvent-treatment and transfer-printing strategies, remain as inevitable challenges due to the inefficient, unstable, and biologically incompatible process. Herein, a scalable fabrication of conducting PEDOT:PSS inks is reported via a metastable liquid−liquid contact (MLLC) method, realizing phase separation and removal of excess PSS simultaneously. MLLC-doped inks are further used to prepare ring-like films through a compromise between the coffee-ring effect and the Marangoni vortex during evaporation of droplets. The specific control over deposition conditions allows for tunable ring-like morphologies and preferentially interconnected networks of PEDOT:PSS nanofibrils, resulting in a high electrical conductivity of 6,616 S cm⁻¹ and excellent optical transparency of the film. The combination of excellent electrical properties and the special morphology enables it to serve as electrodes for touch sensors with gradient pressure sensitivity. These findings not only provide new insight into developing a simple and efficient doping method for commercial PEDOT:PSS ink, but also offer a promising self-assembled deposition pattern of organic semiconductor films, expanding the applications in flexible electronics, bioelectronics as well as photovoltaic devices.     

Improved thermoelectric performance of PEDOT:PSS films prepared by polar-solvent vapor annealing method

To improve thermoelectric performance, polar-solvent vapor annealing (PSVA) method was introduced into the preparation of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. The solvent vapors included dimethyl sulfoxide, ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and deionized water (H₂O). The PSVA-treated PEDOT:PSS films exhibited significantly enhanced electrical conductivity and the maximum value was up to 496 S cm^?1. Especially, utilizing the PSVA method, H₂O could also remarkably enhance the electrical conductivity of pristine PEDOT:PSS film from 0.2 to 57 S cm^?1. There was no distinct change for the Seebeck coefficient of PSVA-treated films with the significantly enhanced electrical conductivity, thereby a maximum power factor of 9.47 μW m^?1 K^?2 at room temperature was obtained. The effects of PSVA method on thermoelectric performance of PEDOT:PSS films were also investigated systematically by analyzing the changes in morphology, carrier mobility and carrier concentration. The results confirmed that PSVA-treated PEDOT:PSS films could obtain smoother morphologies and realize the simultaneous increase of carrier mobility and carrier concentration, which results in the improvement of the thermoelectric performance.     

Phase-Modulated Multidimensional Perovskites for High-Sensitivity Self-Powered UV Photodetectors

2D Ruddlesden-Popper perovskites (PVKs) have recently shown overwhelming potential in various optoelectronic devices on account of enhanced stability to their 3D counterparts. So far, regulating the phase distribution and orientation of 2D perovskite thin films remains challenging to achieve efficient charge transport. This work elucidates the balance struck between sufficient gradient sedimentation of perovskite colloids and less formation of small-n phases, which results in the layered alignment of phase compositions and thus in enhanced photoresponse. The solvent engineering strategy, together with the introduction of poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS) and PC₇₁BM layer jointly contribute to outstanding self-powered performance of indium tin oxide/PEDOT:PSS/PVK/PC₇₁BM/Ag device, with a photocurrent of 18.4 µA and an on/off ratio up to 2800. The as-fabricated photodetector exhibits high sensitivity characteristics with the peak responsivity of 0.22 A W⁻¹ and the detectivity up to 1.3 × 10¹² Jones detected at UV-A region, outperforming most reported perovskite-based UV photodetectors and maintaining high stability over a wide spectrum ranging from UV to visible region. This discovery supplies deep insights into the control of ordered phases and crystallinity in quasi-2D perovskite films for high-performance optoelectronic devices.     

DMSO-treated flexible PEDOT:PSS/PANi fiber electrode for high performance supercapacitors

Wearable energy storage device nowadays gains great interest due to sharply increased demand for highly flexible, stretchable and embedded electronics, where fiber-based supercapacitor (FSC) is a competitive counterpart. The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/ polyaniline (PEDOT:PSS/PANi) fiber has been prepared via an accessible technique of one-dimensional (1D) self-assembly. Nevertheless, PSS as the main cross-linking matrix may lead to more hopping sites for charge carriers, lessening the continuous electrically conductive path. Herein, PEDOT:PSS/PANi fiber was treated with dimethyl sulfoxide (DMSO) to remove the insulative PSS chains. Coupling high electroactivity of PANi and high conductivity of PEDOT, the optimized DMSO-PEDOT:PSS/PANi fiber displays enhanced electrochemical properties with a high specific capacitance (C_s) of 367.7 F g^?1 at 0.5 A g^?1 and good rate capability. Moreover, a symmetric FSC based on the DMSO-P₄P₆ fiber exhibits a high energy density of 42.4 Wh kg^?1 at a power density of 302.3 W kg^?1.

Graphical abstract

PEDOT: PSS/PANi fibers are prepared via a simple technique of one-dimensional (1D) self-assembly, and the PEDOT: PSS/PANi fiber exhibits superior flexibility, electrical conductivity, and electrochemical properties.

     

Nonvolatile write-once-read-many-times memory device with functionalized-nanoshells/PEDOT:PSS nanocomposites

We have investigated the memory effect of the nanocomposites of functionalized carbon nanoshells (f-CNSs) mixed with poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate (PEDOT:PSS) polymer. The f-CNSs were synthesized by the spray pyrolysis method and functionalized in situ with functional groups (OH, COOH, C-H, C-OH) with the aim of improving their compatibility in the aqueous dispersion of PEDOT:PSS. The current-voltage (I-V) sweep curves at room temperature for the Al/f-CNSs, for certain concentrations range, embedded in a PEDOT:PSS layer/Al devices showed electrical bistability for write-once-read-many-times (WORM) memory devices. The memory effect observed in the devices can be explained due to the existence of trapped charges in the f-CNSs/PEDOT:PSS layer. The carrier transport mechanisms for the memory devices is studied and discussed.     

Conductivity enhancement of conjugated polymer after HCl-methanol treatment

Polymer conductivity is key factor to improve the performance of the electronic and photonic devices. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) films were soaked into 0.03, 0.14, 0.41, and 1.13 M concentrations of HCl-methanol solution for 10, 20, 30, 40, 50, 60, and 70 min. The resulting films were investigated using Fourier transform infrared (FTIR) spectrometry, conductivity measurements, and field emission scanning electron microscopy. The characteristic FTIR absorption peaks of poly(4-styrenesulfonate) (PSS) of the films decreased as the soaking time increased. While PSS absorption peaks appeared in the HCl-methanol soaking solution and increased with the soaking time. The conductivity of PEDOT:PSS film was approximately 1.20 × 10^− 6 S/cm before soaking in the HCl-methanol solution. The conductivity of PEDOT:PSS was enhanced nearly three orders of magnitude after soaking the films into the HCl-methanol solvent. The surface of PEDOT:PSS film was initially very smooth. However, numerous humps appeared on the surface of the films after soaking PEDOT:PSS film into the HCl-methanol solution for 10, 20, and 30 min. The number of humps was reduced and disappeared thereafter.     

Electrical properties of polymer/metal interface in polymer light-emitting devices: electron injection barrier suppression

The electrical characterization of a high efficient multilayer polymer light emitting diode using poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] as the emissive layer and an anionic fluorinated surfactant as the electron transport layer was performed. For the sake of comparison, a conventional single layer device was fabricated. The density current vs. voltage measurements revealed that the conventional device has a higher threshold voltage and lower current compared to the surfactant modified device. The effective barrier height for electron injection was “suppressed”. The influence of the interfaces and bulk contributions to the dc and high frequencies conductivities of the devices was also discussed.     

Effects of (NH4)2Sx treatment on the electrical and optical properties of indium tin oxide/conducting polymer electrodes

In this study, the effects of (NH₄)₂S_x treatment on the electrical and optical properties of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) electrodes were researched. The authors found that (NH₄)₂S_x treatment could result in suppressing the hysteresis-type current-voltage characteristics related to the interfacial capacitance variation and a reduction in the equivalent refractive index of the ITO/PEDOT:PSS electrodes, owing to the improvement in the interfacial stability of the ITO/PEDOT:PSS electrodes and a reduction in the interface trap-states related charge store at the ITO/PEDOT:PSS interface. This implies that the ITO/PEDOT:PSS electrodes fabricated using the (NH₄)₂S_x-treated ITO may produce a higher extraction efficiency for ITO/PEDOT:PSS-based optoelectronic devices.     

High‐Performance Inverted Planar Perovskite Solar Cells Enhanced by Thickness Tuning of New Dopant‐Free Hole Transporting Layer

A new hole transporting material (HTM) named DMZ is synthesized and employed as a dopant‐free HTM in inverted planar perovskite solar cells (PSCs). Systematic studies demonstrate that the thickness of the hole transporting layer can effectively enhance the morphology and crystallinity of the perovskite layer, leading to low series resistance and less defects in the crystal. As a result, the champion power conversion efficiency (PCE) of 18.61% with J_SC = 22.62 mA cm^?2, V_OC = 1.02 V, and FF = 81.05% (an average one is 17.62%) is achieved with a thickness of ≈13 nm of DMZ (2 mg mL^?1) under standard global AM 1.5 illumination, which is ≈1.5 times higher than that of devices based on poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT:PSS). More importantly, the devices based on DMZ exhibit a much better stability (90% of maximum PCE retained after more than 556 h in air (relative humidity ≈ 45%–50%) without any encapsulation) than that of devices based on PEDOT:PSS (only 36% of initial PCE retained after 77 h in same conditions). Therefore, the cost‐effective and facile material named DMZ offers an appealing alternative to PEDOT:PSS or polytriarylamine for highly efficient and stable inverted planar PSCs.     

Photo- and electro-luminescent properties of 5,10,15,20-tetra-p-tolyl-21H,23H-porphine doped poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] films

In this work we studied both photoluminescence (PL) and electroluminescence (EL) properties of 5, 10, 15, 20-tetra-p-tolyl-21H, 23H-porphine (TTP) doped poly[2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) with the weight percentages of 0, 0.5, 1, 3, 5, 8 and 12, respectively. In the process of PL the significant energy transfer occurs from MEH-PPV to TTP, even though there is a small spectral overlap between the absorption of TTP and the emission of MEH-PPV. For investigation of the process of EL a series of organic light-emitting diodes were fabricated with the device structure of ITO/PEDOT:PSS/TTP-doped polymer layer/Al (ITO = Indium Tin Oxides; PEDOT:PSS = poly (3,4-oxyethyleneoxythiophene): poly-(styrene sulfonate)). In devices in which the TTP was present at 5% the emission of EL was dominated by TTP; at lower doping levels MEH-PPV emission dominated. Moreover, multi-color emission was observed at the doping level below 5%. On the other hand, the mechanism for the EL process was reported.     

Parameter extraction applied to the de-doping of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styenesulphonate)) thermoelectrics

A recent report suggested that de-doping (reducing the volume of the dopants) could improve the figure-of-merit of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styenesulphonate)) thermoelectrics through a simultaneous decrease in the thermal conductivity and an increase in the electrical conductivity. While this had been shown to increase the values of ZT, better understanding on the physics would be desirable. This work analyzed the transport data reported by Kim et al. (Nat Mater 12:719–723, 2013) on PEDOT:PSS and evaluated the changes in the materials parameters during de-doping. Our results showed that moderate de-doping had the effect of increasing the carrier mobility while at the same time it decreased somewhat the carrier density. Matching the mobilities computed from the thermal and electrical conductivity data and from theory allowed us to evaluate the width of the density of states σ, the values of the site spacing a′ and the localization length L for a known value of the escape frequency ν_ph. As observed, both L and a′ increased moderately with de-doping while their ratio L/a′ also increased from 0.44 to 0.55 over the ethylene glycol treatment range (up to 200 min). This suggested that de-doping not only reduced the PSS volume and the film thickness but also brought about improvement in the charge transport. The computed value of σ was amazingly small (only ~3.8 meV) contributing to the better thermoelectric performance.     

Microstructural effects on the phase transitions and the thermal evolution of elastic and piezoelectric properties in highly dense,submicron-structured NaNbO<Subscript>3</Subscript> ceramics

The dielectric, piezoelectric and elastic coefficients, as well as the electromechanical coupling factors, of NaNbO₃ submicron-structured ceramics have been obtained by an automatic iterative method from impedance measurements at resonance. Poled thin discs were measured from room temperature up to the depoling one, close to 300 °C. Dielectric thermal behaviour was determined also for unpoled ceramics up to the highest phase transition temperature. Ceramics were processed by hot-pressing from mechanically activated precursors. Microstructural effects on the properties are discussed. The suppression of the classical maximum in dielectric permittivity in unpoled ceramics at the phase transition at 370 °C was found when a bimodal distribution of grain sizes, with a population of average grain size of 110 nm in between much coarser grains, is observed. The appearance of a phase transition at 150 °C took place when Na vacancies are minimised. The occurrence of a non-centrosymmetric, ferroelectric phase, in the unpoled ceramic from room temperature to ~300 °C, highly polarisable resulting in high ferro–piezoelectric properties was also observed in the ceramic which presents grain size below 160 nm. Maximum values of k _p = 14%, d ₃₁ = −8.7 × 10⁻¹² C N⁻¹ and N _p = 3772 Hz m at room temperature, and k _p = 18%, d ₃₁ = −25.4 × 10⁻¹² C N⁻¹ and N _p = 3722 Hz m at 295 °C were achieved in the best processing conditions of the ceramics.     

Fabrication of flexible conductive films derived from poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) (PEDOT:PSS) on the nonwoven fabrics substrate

In this research, conducting poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonic acid) (PEDOT:PSS) aqueous dispersion was synthesized at first via chemical oxidative polymerization and followed by mixing it with poly(styrene-r-butyl acrylate) P(St-BA) aqueous latex, creating a conductive material with outstanding stretchability. The elastic conductive composite were then film formed on the glass and poly(ethylene terephthalate) (PET) nonwoven fabric substrate by spin coating and dip coating, respectively. Composite films with various contents of PEDOT:PSS polymer (10–100 wt.%) had been prepared. From the conductivity measurements, the conductivity was still kept as high as 88 S cm⁻¹ even the PEDOT:PSS content was lowered to 10 wt.%. Furthermore, the elasticity of conductive films on the PET-nonwoven fabric substrate was evaluated by the 180° bending test repeating 100 times. With introducing soft P(St-BA) material in the PEDOT:PSS phase, the surface resistance increased merely 3–6 times after bending 100 times, while the surface resistance for pure PEDOT:PSS film could reach 18–20 times.     

Synthesis and photovoltaic properties of conjugated copolymers bearing planar acenaphtho[1,2-b]quinoxaline moiety with deep HOMO level

A series of alternating copolymers (PC-AQx, PT-DTAQx, PC-DTAQx, PF-DTAQx, and PBDT-DTAQx) bearing novel planar acenaphtho[1,2-b]quinoxaline (AQx) or 8,11-di(thiophen- 2-yl)acenaphtho[1,2-b]quinoxaline (DTAQx)-acceptor cores have been synthesized via Suzuki or Stille coupling reactions. UV–vis absorption and GIXRD characterization results indicated that the presence of planar DTAQx unit is favorable for the promotion of well-ordered interchain packing in the solid state, and the incorporation of planar electron-donating benzo[1,2-b: 4,5-b′]-dithiophene (BDT) moiety would be propitious to the molecular self-organization. Electrochemical measurement results suggested that four copolymers possess deep HOMO energy level of −5.5 ~ −5.6 eV. The polymer solar cell with structure of ITO/PEDOT:PSS(30 nm)/polymer:PCBM (60 nm)/Bphen(10 nm)/Ag(100 nm) exhibited the highest V _oc of 0.84 V with PF-DTAQx as p-type polymer, while the best power conversion efficiency (PCE) of 0.9 % was obtained using a blend of PBDT-DTAQx and PCBM (1:4) as active layer.     

Luminescence properties and electronic structure of Sm<Superscript>3+</Superscript>-doped YAl<Subscript>3</Subscript>B<Subscript>4</Subscript>O<Subscript>12</Subscript>

The luminescence properties of Sm³⁺ ions in YAl₃B₄O₁₂ were studied upon synchrotron excitation in the 3.8–11 eV region. In addition to the 4f → 4f excitation bands, the excitation spectra of the Sm³⁺ emission contain broad bands at 6.1 and ~7.0 eV. These bands are attributed to charge transfer transition in Sm³⁺–O²⁻ complexes and 4f → 5d transition of Sm³⁺ ions, respectively. The optical absorption edge of YAl₃B₄O₁₂ was determined at 7.3 eV. A comparison with the results of electronic structure calculations on YAl₃B₄O₁₂ is also made.     

Performance enhancement of polymer Schottky diode by doping pentacene

Schottky diodes have been fabricated using pentacene-doped poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) as a semiconducting material. To understand the fundamental properties of the pentacene-doped PEDOT:PSS, ultraviolet visible (UV) absorption spectroscopy was employed. It was found that a significant amount of pentacene can dissolve in n-methylpyrrolidone solvent. No characteristic absorption peak of pentacene was observed in the UV-visible spectra of PEDOT:PSS films doped with pentacene,. However, the absorption intensity of the doped PEDOT:PSS films increased as the pentacene concentration increased in particular in the UV region. The atomic force microscope images show that the surface roughnesses of PEDOT:PSS films increased as the pentacene concentration increased. Three-layer Schottky diodes comprising Al/PEDOT:PSS/Au or Al/PEDOT:PSS-pentacene/Au were fabricated. The maximum forward currents of non-doped and doped Schottky diodes were 4.8 and 440 µA/cm² at 3.3 MV/m, respectively. The forward current increased nearly two orders of magnitude for Schottky diode doped with 11.0 wt.% of pentacene.     

Conductivity enhancement of PEDOT:PSS thin film using roll to plate technique and its characterization as a Schottky diode

The conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) was improved by pressing the PEDOT:PSS thin film using roll to plate system. PEDOT:PSS thin film was deposited on polyethylene terephthalate using electrohydrodynamics atomization technique. The physico-chemical properties of the pressed thin film at different loads were compared with an un-pressed sample. The electrical properties show that the film conductivity has been increased by four times. An optimized pressing load was found to have good conductivity and transmittance of the thin film. A hybrid device (PEDOT:PSS/F8BT/ZnO/Ag) was fabricated using layer by layer method with PEDOT:PSS as anode. The I–V characterization showed that the device with pressed PEDOT:PSS showed higher current densities. The results give a promising future of PEDOT:PSS in electronics device applications using printed electronics techniques.     

Preparation of a working electrode with a conducting PEDOT:PSS film and its applications in a dye-sensitized solar cell

This study investigates the applicability of a working electrode with a poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film on a dye-sensitized solar cell (DSSC). This working electrode was designed and fabricated by inserting a PEDOT:PSS film between a fluorine-doped tin oxide (FTO) glass substrate and a layer of nanocrystalline TiO₂ particles (P-25). This study also examines the effects of annealing temperature and duration on the transmittance and microstructure of a PEDOT:PSS film as well as the power conversion efficiency of DSSC with this film. The power conversion efficiency of a DSSC with a PEDOT:PSS film (6.37%) substantially exceeds that of a conventional DSSC (4.24%). This result is attributed to the fact that this transparent and conductive PEDOT:PSS film deposited on the FTO glass substrate using a simple spin coating method substantially improves the short-circuit photocurrent per unit area and the fill factor of DSSC.     

Enhancement-Mode PEDOT:PSS Organic Electrochemical Transistors Using Molecular De-Doping

Organic electrochemical transistors (OECTs) show great promise for flexible, low-cost, and low-voltage sensors for aqueous solutions. The majority of OECT devices are made using the polymer blend poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), in which PEDOT is intrinsically doped due to inclusion of PSS. Because of this intrinsic doping, PEDOT:PSS OECTs generally operate in depletion mode, which results in a higher power consumption and limits stability. Here, a straightforward method to de-dope PEDOT:PSS using commercially available amine-based molecular de-dopants to achieve stable enhancement-mode OECTs is presented. The enhancement-mode OECTs show mobilities near that of pristine PEDOT:PSS (≈2 cm² V⁻¹ s⁻¹) with stable operation over 1000 on/off cycles. The electron and proton exchange among PEDOT, PSS, and the molecular de-dopants are characterized to reveal the underlying chemical mechanism of the threshold voltage shift to negative voltages. Finally, the effect of the de-doping on the microstructure of the spin-cast PEDOT:PSS films is investigated.