PSS-based Device Research Articles

High-Yield Exfoliation of Stanene Nanodots for High-Performance Organic Light-Emitting Diodes.

Stanene nanodots (SnNDs) derived from layered tin have attracted considerable interest due to their conveniently tunable bandgap and topological superconductivity. However, high-yield exfoliation of ultrathin SnNDs is still a challenge due to the short layer spacing and strong binding energy. In this work, atomically thin SnNDs with a uniform size of 2.3 nm are successfully prepared by utilizing imidazolium ionic liquid-assisted exfoliation. The obtained SnNDs possess a wide bandgap of 2.69 eV, along with notable solvent compatibility (well dispersed in both polar and nonpolar solvents) and excellent stability. Furthermore, we construct Ir(ppy)3-based green OLED with hybridizing SnNDs and graphene oxide (GO) as the hole injection layer (HIL). It proves that the application of SnNDs helps to modulate the work function and passivate surface defects of GO, increasing hole mobility and thereby improving the device performance. Compared to the PEDOT:PSS-based control device, the optimized SnNDs-GO-based OLED demonstrates an improvement of 6.56, 41.06, and 8.16% in current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE), respectively. This work not only introduces a new approach to preparing 2D SnNDs but also creates a novel HIL material for OLED devices.

A Flexible Electrochromic Device based on PEDOT: PSS Working in Visible and Infrared Band

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a novel conducting polymer, has gained significant attention in the realm of electrochromism. In this study, we present the fabrication of a simple double-layer device utilizing PEDOT:PSS, which successfully achieves precise control of emissivity in the infrared band. Through comprehensive experimentation, we observe an impressive regulation amplitude of 0.25 and a temperature difference of 10°C, relative to a background temperature of 100°C. Additionally, the device exhibits remarkable flexibility compared to other existing devices. These findings demonstrate the potential of PEDOT:PSS-based double-layer devices as versatile tools for infrared emissivity modulation, holding promise for diverse applications in fields such as thermal management and energy-efficient technologies.

PEDOT-based stretchable optoelectronic materials and devices for bioelectronic interfaces.

The rapid development of wearable and implantable electronics has enabled the real-time transmission of electrophysiological signals in situ, thus allowing the precise monitoring and regulation of biological functions. Devices based on organic materials tend to have low moduli and intrinsic stretchability, making them ideal choices for the construction of seamless bioelectronic interfaces. In this case, as an organic ionic-electronic conductor, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has low impedance to offer a high signal-to-noise ratio for monitoring bioelectrical signals, which has become one of the most promising conductive polymers. However, the initial conductivity and stretchability of pristine PEDOT:PSS are insufficient to meet the application requirements, and there is a trade-off between their improvement. In addition, PEDOT:PSS has poor stability in aqueous environments due to the hygroscopicity of the PSS chains, which severely limits its long-term applications in water-rich bioelectronic interfaces. Considering the growing demands of multi-function integration, the high-resolution fabrication of electronic devices is urgent. It is a great challenge to maintain both electrical and mechanical performance after miniaturization, particularly at feature sizes below 100 μm. In this review, we focus on the combined improvement in the conductivity and stretchability of PEDOT:PSS, as well as the corresponding mechanisms in detail. Also, we summarize the effective strategies to improve the stability of PEDOT:PSS in aqueous environments, which plays a vital role in long-term applications. Finally, we introduce the reliable micropatterning technologies and PEDOT:PSS-based stretchable optoelectronic devices applied at bio-interfaces.

NiOx Nanoparticles Hole-Transporting Layer Regulated by Ionic Radius-Controlled Doping and Reductive Agent for Organic Solar Cells with Efficiency of 19.18.

Nickel oxide (NiOx ) has garnered considerable attention as a prospective hole-transporting layer (HTL) in organic solar cells (OSCs), offering a potential solution to the stability challenges posed by traditional HTL, PEDOT:PSS, arising from acidity and hygroscopicity. Nevertheless, the lower work function (WF) of NiOx relative to donor polymers reduces charge injection efficiency in OSCs. Herein, NiOx nanoparticles are tailored through rare earth doping to optimize WF and the impact of ionic radius on their electronic properties is explored. Lanthanum (La3+ ) and yttrium (Y3+ ) ions, with larger ionic radii, are effectively doped at 1 and 3%, respectively, while scandium (Sc3+ ), with a smaller ion radius, allows enhanced 5% doping. Higher doping ratios significantly enhance WF of NiOx . A 5% Sc3+ doping raises WF to 4.99eV from 4.77eV for neat NiOx while maintaining high conductivity. Consequently, using 5% Sc-doped NiOx as HTL improves the power conversion efficiency (PCE) of OSCs to 17.13%, surpassing the 15.64% with the neat NiOx . Further enhancement to 18.42% is achieved by introducing the reductant catechol, outperforming the PEDOT:PSS-based devices. Additionally, when employed in a ternary blend system (D18:N3:F-BTA3), an impressive PCE of 19.18 % is realized, top-performing among reported OSCs utilizing solution-processed inorganic nanoparticles.

Design of a simple bifunctional system as a self-assembled monolayer (SAM) for inverted tin-based perovskite solar cells

In this work, we functionalized the ITO substrates with a series of self-assembled monolayer (SAM) molecules to improve the hole extraction ability of the electrodes and retard the charge recombination with the devices in an inverted planar p-i-n configuration. Organic molecules with simple structures, namely 4-aminobenzoic acid (AB), 4-(2-aminomethyl)benzoic acid (AM), 4-(2-aminoethyl)benzoic acid (AE), and 4-nitrobenzoic acid (NB) were chosen to functionalize the ITO substrates via simple immersion method to form hole-selective SAM on ITO. The TPSCs were fabricated according to a two-step sequential deposition approach using a co-solvent system, and the AB device was found to exhibit an attractive efficiency of power conversion (PCE) of 7.6 % while the other SAM-based devices showed poorer performance. The AB device also displayed impressive long-term storage stability by maintaining about 80 % of its initial efficiency for over 3500 h without encapsulation, in addition to a long-term (6 h) light-soaking stability, which is superior to the PEDOT: PSS-based device in ambient conditions. The SAM/perovskite interfacial characteristics were studied using UPS, EIS, and TCSPC to understand the energy levels, charge recombination, and hole-extraction nature, respectively, and to support the outstanding performance and stability of the AB device.

Demonstration of high-stable bipolar resistive switching and bio-inspired synaptic characteristics using PEDOT:PSS-based memristor devices

Demonstration of high-stable bipolar resistive switching and bio-inspired synaptic characteristics using PEDOT:PSS-based memristor devices

A Direct surface modification strategy of ITO anodes enables high-performance organic photodetectors

A direct modification strategy of indium tin oxide (ITO) for high-performance organic photodetectors (OPDs) is developed. By using chlorinated ITO (ITO-Cl) as the anode, the OPD device exhibits superior performance than ITO/PEDOT:PSS-based device.

SnOx as Bottom Hole Extraction Layer and Top In Situ Protection Layer Yields over 14% Efficiency in Sn-Based Perovskite Solar Cells

Sn-based perovskite solar cells (S-PSCs) are a promising candidate to replace toxic Pb-based PSCs. For promoting their industrial application, developing inorganic substitutions of unstable poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is also an important part due to its intrinsic stability and low cost. Here, we in situ prepared ambipolar SnOx by a simple and fast plasma-assistant strategy (P-SnOx). The as-prepared P-SnOx works as a hole transport layer directly, yielding a 10.89 ± 0.51% power conversion efficiency (PCE) comparable to a PEDOT:PSS-based device (10.39 ± 0.72%). The top SnOx (T-SnOx), composed of SnO2 and Sn metal, as a modifier and a protection layer of the perovskite by reducing Sn4+ to Sn2+, gives a 13.08 ± 0.33% device performance. This in situ top protective strategy combined with P-SnOx as a hole transport layer further boosts the champion PCE of S-PSCs to 14.09% (13.5 ± 0.32%).

Annealing-Insensitive, Alcohol-Processed MoOx Hole Transport Layer for Universally Enabling High-Performance Conventional and Inverted Organic Solar Cells.

At present, most solution-processed molybdenum oxide (s-MoOx) hole transport layers (HTLs) are still mainly used in conventional organic solar cells (OSCs) but unsuitable for inverted OSCs. Herein, we demonstrate for the first time an annealing-insensitive, alcohol-processed MoOx HTL that can universally enable high-performance conventional and inverted OSCs. The s-MoOx HTL is spin-coated from the MoOx nanoparticle dispersion in alcohol, where the MoOx nanoparticles are synthesized by simple nonaqueous pyrolysis conversion of MoO2(acac)2. The MoOx nanoparticles possess uniform and very small sizes of less than 5 nm and can be well dispersed in alcohol, so the s-MoOx HTLs on ITO and active layer both show an overall uniform and smooth surface, suitable for conventional and inverted OSCs. In addition, the s-MoOx HTL possesses decent optical transmittance and appropriate work function. Utilizing the s-MoOx HTL annealed between room temperature and 110 °C and PM6:Y6 active layer, the conventional OSCs show an excellent power conversion efficiency (PCE) of 16.64-17.09% and the inverted OSCs also show an excellent PCE of 15.74-16.28%, which indicate that the s-MoOx HTL could be annealing-insensitive and universal for conventional and inverted OSCs. Moreover, conventional and inverted OSCs with the s-MoOx HTLs annealed at 80 °C both exhibit optimal PCEs of 17.09 and 16.28%, respectively, which are separately superior than that of the PEDOT:PSS-based conventional OSCs (16.94%) and the thermally evaporated MoO3 (e-MoO3)-based inverted OSCs (16.03%). Under light soaking and storage aging in air, the unencapsulated inverted OSCs based on the s-MoOx HTL show similarly excellent ambient stability compared to the e-MoOx-based devices. In addition, the s-MoOx HTL also shows a universal function in conventional and inverted OSCs with PBDB-T:ITIC and PM6:L8-BO active layers. Notably, the s-MoOx-based conventional and inverted OSCs with the PM6:L8-BO active layer exhibit very excellent PCEs of 18.21 and 17.12%, respectively, which are slightly higher than those of the corresponding PEDOT:PSS-based device (18.17%) and e-MoO3-based device (17.00%). The annealing-insensitive, alcohol-processed MoOx HTL may be very promising for flexible and large-scale processing conventional/inverted OSCs.

Cl2-Doped CuSCN Hole Transport Layer for Organic and Perovskite Solar Cells with Improved Stability

Copper(I) thiocyanate (CuSCN) is a wide bandgap and solution-processable p-type semiconductor with tremendous potential for large-area optoelectronic applications. In this work, chlorine-doped CuSCN (Cl2–CuSCN) was utilized to form a hole transport layer (HTL) for different organic solar cells (OSCs) and inverted perovskite solar cells (PSCs). Chlorine doping into CuSCN thin films is found to improve the device performance of different OSCs, to a level comparable to that of PEDOT:PSS-based OSCs. Notably, the inverted PSCs with Cl2–CuSCN showed a better performance than those with pristine CuSCN or PEDOT:PSS-based inverted PSC devices. Moreover, Cl2–CuSCN-based OSCs and PSCs also reveal significantly better stability than pristine CuSCN and PEDOT:PSS-based devices. Our results show how Cl2–CuSCN thin films act as a universally applicable HTL for emerging solar cell technologies, improving both device performance and stability.

UV-ozone treated Ti3C2Tx-MXene nanosheets as hole injection layer for organic light-emitting diodes

In this work, we successfully synthesized Ti3C2Tx-MXene nanosheets with a lateral dimension of 1 ∼ 2 μm by using wet-chemical etchant and sonication-assisted liquid-phase exfoliation method. After UV-ozone treatment, the work function for Ti3C2Tx-MXene nanosheets was adjusted to 5.14 eV well matching to indium tin oxide (ITO) anode (4.80 eV). Using Ti3C2Tx-MXene nanosheets as hole injection layer (HIL), Ir(ppy)3-based green organic light-emitting diodes (OLEDs) were fabricated, and the resulting devices exhibit a low turn-on voltage of 3.0 V and the high current efficiency, power efficiency and external quantum efficiency of 72.79 cd/A, 54.44 lm/W and 20.34 %, which are obviously better than these of 67.38 cd/A, 50.38 lm/W and 18.65 % for PEDOT:PSS-based reference device. Further, FIrpic- and Ir(pq)2acac-based blue and red OLEDs with Ti3C2Tx-MXene nanosheets HIL were demonstrated, which also show the significantly improved device efficiency of 44.56 cd/A, 32.44 lm/W and 22.07 % for blue device and 39.17 cd/A, 38.54 lm/W and 21.90 % for red device than these for corresponding PEDOT:PSS-based devices, proving the universal applicability of Ti3C2Tx-MXene nanosheets as HIL in OLEDs. The higher performance for Ti3C2Tx-MXene nanosheets-based devices can be attributed to the appropriate work function, high transmittance, high carrier mobility and good film forming property for Ti3C2Tx-MXene nanosheets. This is the first report about the MXene using as HIL in OLEDs, which opens up a new way to develop high-performance holes injection materials for solution-processed OLEDs.

Performance improvement of organic solar cells using a hybrid hole transport layer of poly(triarylamine) and molybdenum trioxide

In this study, we improved the performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′] dithiophene-co-3-fluorothieno [3,4-b]thiophene-2-carboxylate] (Liu et al., 2020; Liu et al., 2020) [6,6]:-phenyl-C 70 -butyric acid methyl ester (PTB7-Th:PC 71 BM)-based organic solar cells (OSCs) by using molybdenum trioxide (MoO 3 ) covered poly(triarylamine) (PTAA) as a hybrid hole transport layer (HTL). Using this technique, an average power conversion efficiency (PCE) of 9.82% was achieved, which was higher than that (8.95%) of OSCs using conventional HTL of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The best performing OSC using PTAA/MoO 3 showed a highest PCE of 10.16%, with a stable power output and negligible hysteresis. Due to the high hydrophobicity of the PTAA/MoO 3 film, the stability of the OSCs was improved simultaneously. After a measurement of 20 days, the PCE degradation was suppressed to 17.5% upon using PTAA/MoO 3 , which was lower than that (28.2%) of PEDOT:PSS-based devices. Additionally, the flexible devices (on polyethylene-naphthalate substrates) showed a high PCE of 8.51%, indicating the good flexibility of PTAA/MoO 3 . • PTAA was protected by MoO 3 and applicable for OSCs. • PCE and stability of the OSCs were improved simultaneously. • PCE of 10.16% was achieved for PTB7-Th:PC 71 BM-based OSCs. • Flexible devices showed a high PCE of 8.51%.

Electrochemically Prepared Polyaniline as an Alternative to Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) for Inverted Perovskite Solar Cells

The goal of this work is to substitute the conventional high-cost poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in inverted perovskite solar cells (PSCs) with an efficient and conducting polyaniline (PANI) polymer. The reported use of PANI in PSCs involves a chemical synthesis method which is prone to contamination with impurities as it requires several materials for polymerization and adhesion improvement with substrates, contributing to low device efficiencies. This work mitigates this issue using an electrochemical method that is low cost, less time consuming, and capable of producing thin films of PANI with excellent adhesion to substrates. Results demonstrated that the power conversion efficiency of the electrochemically synthesized PANI-based PSC is 16.94% versus 15.11% for the PEDOT:PSS-based device. It was observed that the work function of PANI was lower compared to that of PEDOT:PSS which decreased VOC but enhanced hole extraction at the hole transport layer/perovskite interface, thus increasing JSC. Doping electrolyte solution with lithium bis(trifluoromethanesulfonyl)imide LiTFSI increased the work function of PANI, thus increasing VOC from 0.87 to 0.93 V. This method enables simple and scalable synthesis of PANI as a competitive hole transport material to replace rather expensive PEDOT:PSS, thus enabling an important step toward low-cost inverted perovskite photovoltaic devices.

Multifunctional n-ZnO/MoO3/PEDOT:PSS-based hybrid device for high-speed UV light detection and ReRAM applications

Multifunctional n-ZnO/MoO3/PEDOT:PSS-based hybrid device for high-speed UV light detection and ReRAM applications

Organic photoelectrochemical transistor detection of tear lysozyme

A high-performance organic photoelectrochemical transistor (OPECT) is developed by synergizing a light-sensitive aptamer/CdS QDs/Ti wire gate photoanode with a PEDOT:PSS-based device towards detection of the tear biomarker lysozyme.

Polymer-based non-volatile resistive random-access memory device fabrication with multi-level switching and negative differential resistance state

Resistive random-access memory (RRAM) has been widely considered for its prospective applicability owing to its non-volatile characteristics. In this study, a polymer-based vacuum-free RRAM device fabricated with the conductive polymer, poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was proposed. Pristine PEDOT:PSS coated on indium tin oxide (ITO) electrode was used as the active layer, while PEDOT:PSS with 16 vol% ethylene glycol was added for the top electrode. The PEDOT:PSS-based RRAM device demonstrated controlled non-volatile bipolar switching and a good ON/OFF ratio with a negative differential resistance effect in the high-voltage range during the RESET process. Multi-level switching was also accomplished by controlling the voltage, which demonstrated reliable and non-volatile switching. The switching mechanism of this polymer RRAM device can be explained through the electrochemical filamentary formation as well as the current-induced phase segregation of PEDOT:PSS near the anode(ITO)/polymer interface. • Vacuum-free and solution-processed fabrication method of a polymer based RRAM device. • Low cost and low temperature (<120 °C) fabrication. • MLC switching during SET process and NDR effect during RSEST process. • Investigation of detailed switching mechanism from literature survey and I–V curve fitting.

Study on graphene oxide as a hole extraction layer for stable organic solar cells.

The development of an efficient and stable hole extraction layer (HEL) is crucial for commercializing organic solar cells (OSCs). Although a few candidates have been widely utilized as HELs for OSCs, the most appropriate material has been lacking. A few articles have recently reported graphene oxide (GO) as a well-working HEL that offers comparable performance to conventional HELs. However, a systematic study providing comprehensive insight into the GO-based OSC behavior is lacking. This article discusses broad topics, including the material properties, device efficiency, shelf lifetime, and impedance properties. We found that GO offers excellent properties, which are identical to those of conventional HELs, while the shelf lifetime shows a significant 6-fold increase. Furthermore, we discuss the significantly reduced space-charge limited region of an aged GO-based OSC compared with a PEDOT:PSS-based device, which is revealed to be a reason for the different shelf lifetime. We believe that the results will accelerate the development of GO as an HEL for OSCs and other optoelectronic devices.

Copper Thiocyanate as an Anode Interfacial Layer for Efficient Near-Infrared Organic Photodetector

Interfacial modification between the electrode and the overlying organic layer has significant effects on the charge injection and collection and thus the device performance of organic photodetectors. Here, we used copper(I) thiocyanate (CuSCN) as the anode interfacial layer for organic photodetector, which was inserted between the anode and an organic light-sensitive layer. The CuSCN layer processed with ethyl sulfide solution presented similar optical properties to the extensively used anode interlayer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), while the relatively shallow conduction band of CuSCN resulted in a much higher electron-injection barrier from the anode and shunt resistance than those of PEDOT:PSS. Moreover, the CuSCN-based device also exhibited an increased depletion width for the PEDOT:PSS-based device, as indicated by the Mott-Schottky analysis. These features lead to the dramatically reduced dark current density of 2.7 × 10-10 A cm-2 and an impressively high specific detectivity of 4.4 × 1013 cm Hz1/2 W-1 under -0.1 V bias and a working wavelength of 870 nm. These findings demonstrated the great potential of using CuSCN as an anode interfacial layer for developing high-performance near-infrared organic photodetectors.

Realization of In:ZnO/PEDOT:PSS based multifunctional device for ultraviolet (UV) light detection and resistive switching memory applications

The present research reports on a hybrid multifunctional device for UV light detection and non-volatile resistive switching memory based on n-In:ZnO/poly 3,4-ethylene dioxythiophene:polystyrene sulfonate (PEDOT:PSS) junctions. Using a spray pyrolysis method, indium (1–5 at. %) doped ZnO thin films (IZO) were deposited on the pre-heated glass substrate. The structural analysis of IZO thin films shows that all the prepared samples exhibit a hexagonal wurtzite structure with preferential orientation along the (101) plane. The morphological analysis shows a uniform distribution of grains without any voids. The optical transmission spectra reveal that IZO thin films show higher transparency (&amp;gt;90%) in the visible region. With an optimum doping concentration of In (4 at. %), the deposited IZO thin films exhibit high carrier concentration and low electrical resistivity value of 4.58 × 1020 cm−3 and 4.01 × 10−2 Ω cm, respectively. The current–voltage (I–V), photoresponse, and resistive switching behavior of the fabricated n-IZO/PEDOT:PSS-based hybrid device was studied. Under an external reverse bias, the device exhibits a high photoresponsivity (R) value of 0.31 A/W and fast photoresponse switching speed with the measured rise and fall time of 0.08 and 1 s, respectively. It was proposed that the formation/rupture of both anionic and cationic conductive filaments plays a crucial role in the obtained resistive characteristics of the fabricated hybrid device.

Bi0.5Sb1.5Te3/PEDOT:PSS-based flexible thermoelectric film and device

Incorporating inorganic thermoelectric fillers into conductive polymers is one promising strategy to develop high-performance flexible thermoelectric films. However, due to the relatively high interfacial contact resistance between fillers and polymers, carriers tend to be scattered at the interfaces during the interfacial transports, which deteriorates the electrical properties of the system, and in turn leads to low energy conversion efficiency. Here, a new strategy is developed to optimize interfacial carrier transports in Bi0.5Sb1.5Te3/PEDOT:PSS composite, by coating Bi0.5Sb1.5Te3 fillers with highly conductive CuTe layer. With highly crystallized PEDOT:PSS prepared as the matrix, high-performance Cu-Bi0.5Sb1.5Te3 /PEDOT:PSS film is fabricated with promising σ of ~2300 S cm−1 and peak S2σ of 312 µW m−1 K−2 at room temperature, which reaches to a record-high value in the reported Bi0.5Sb1.5Te3/PEDOT:PSS composites. Accordingly, a home-made flexible thermoelectric device is fabricated using our prepared composites, generating a promising open-circuit thermovoltage of ~7.7 mV with the human wrist as the thermal source. This study addresses the significance of interfacial carrier transport, hinting the bright prospects of cheap conductive polymers as the effective power source of wearable electronics.