PSS Layer Research Articles

Novel solution-processable light filter approaches for light detection purpose in Lab-on-Chip-Systems

In this contribution, two approaches of the solution processing of novel spectral light filters are demonstrated. The first approach shows the combination of light filtering capability with electrical conductivity in a “light filter electrode” by mixing colorants into poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink. Different colorants are investigated concerning their influence on the workfunction and the electrical conductivity of the resulting PEDOT:PSS layers. In addition, these electrodes could be integrated into organic photodiodes, opening up the possibility of using the whole device for specific light detection. Within the second approach, the surface plasmon resonance and the scattering of metal nanoparticles is used for light filtering. Light scattering (and therefore the reflection of excitation light back into the microfluidic channel) increases the excitation efficiency, thus increasing the intensity of the fluorescent light. With this approach, the sensitivity of the demonstrated light detectors can effectively be increased while simultaneously decreasing the detection limit of the substance of interest.

Graphene/Fluorinated Graphene Systems for a Wide Spectrum of Electronics Application

Heterostructures prepared from graphene and fluorographene (FG) using the technology of 2D printing on solid and flexible substrates were fabricated and studied. Excellent stability of printed graphene layers and, to a lesser degree, composite graphene: PEDOT: PSS layers were shown. Extraordinary properties of FG as an insulating layer for graphene-based heterostructures at fluorination degree above 30% were demonstrated. It is shown that the leakage current in thin (20-40 nm) films is normally smaller than 10^-8 A/cm2, the breakdown field being greater than 108 V/cm. In hybrid structures with printed FG layers in which graphene was transferred onto, or capsulated with, an FG layer, an increase in charge-carrier mobility and material conductivity amounting to 5-6 times was observed. The spectrum of future applications of FG layers can be further extended due to the possibility of obtaining, from weakly fluorinated graphene (< 20%), functional layers exhibiting a negative differential resistance behavior and, at fluorination degrees of 20-23%, field-effect-transistor channels with current modulation reaching several orders. Composite or bilayer films based on fluorographene and V2O5 or polyvinyl alcohol exhibit a stable resistive switching behavior. On the whole, graphene/FG heterostructures enjoy huge potential for their use in a wide spectrum of application, including flexible electronics.

Doping of Hole Transport Layer PEDOT: PSS with Pentacene for PCDTBT: PCBM Based Organic Solar Cells

Organic photovoltaics are a renewable form of energy with benefits such as solution process ability, low cost environment friendly production methods and flexible substrates. In this paper we discuss about the doping of hole transport layer PEDOT:PSS with pentacene in PCDTBT Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl- organic solar cells using 2′,1′,3′-benzothiadiazole)]:PC70BM (phenyl C71 butyric acid methyl ester) based organic solar cell with the device structure (Glass/ITO/PEDOT:PSS doped with pentacene/ PCDTBT:PCBM/ Ca/Al.) The performance characteristics are evaluated by increasing the amount of pentacene and the annealing temperature of the pentacene doped PEDOT: PSS layer. When the amount of pentacene was increased, transmittance is increased which in turn allows more light to reach the active layer. As the annealing temperature is increased, agglomeration of PEDOT: PSS is observed. The films of pentacene-doped PEDOT: PSS were characterized by UV-vis transmittance AFM (atomic force microscopy) and FESEM (scanning electron microscope).

Thermodynamically self-organized hole transport layers for high-efficiency inverted-planar perovskite solar cells.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a popular and promising hole transport material for making efficient inverted-planar perovskite solar cells (IP-PSCs). However, the mismatch between the work function of conventional PEDOT:PSS and the valence band maximum of perovskite materials is still a challenge for efficient hole extraction. Here, we report systematic studies on the work-function modification and thermodynamic morphological evolution of PEDOT:PSS films by tuning the PSS/PEDOT ratio, along with its effects on the photovoltaic responses of IP-PSCs. We found that the open-circuit voltage (VOC) of an IP-PSC could be enhanced by controlling the work function of PEDOT:PSS. Furthermore, the optical transmittance of the PEDOT:PSS film could be maximized by controlling the morphological evolution, which will further increase the short-circuit current density (JSC) of the IP-PSC. The VOC and JSC of the IP-PSC with the optimized PEDOT:PSS composition increased from 0.88 to 0.93 V and from 17.11 to 20.77 mA cm-2, respectively, compared with an IP-PSC containing commercial PEDOT:PSS, which results in a power conversion energy that is greatly improved from 12.39 to 15.24%.

PEDOT:PSS Overcoating Layer for Mechanically and Chemically Stable Ag Nanowire Flexible Transparent Electrode

We investigated the effect of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) deposition on the chemical and mechanical stability of Ag nanowire flexible electrodes. A large number of bending cycles, up to 500,000 cycles, were imposed on the Ag nanowire electrodes with and without PEDOT:PSS overcoating layer. In situ resistance measurement during bending tests revealed that the Ag nanowire electrode with PEDOT:PSS overcoating layer was mechanically reliable, showing a 21.9% increase in resistance after 500,000 cycles of bending. Scanning electron microscope images revealed that the failure of the Ag nanowire network occurred along with cracks initiated in the PEDOT:PSS layer, which resulted in the increase in resistance under bending. Furthermore, the PEDOT:PSS deposition enhanced the chemical stability of Ag nanowire electrode, which showed no significant increase in resistance after exposure in air for 50 days. Our study underscored that PEDOT:PSS is effective in protecting the Ag nanowires, while maintaining the high mechanical stability.

Contact-printed ultrathin siloxane passivation layer for high-performance Si-PEDOT:PSS hybrid solar cells

A simple way for high-performance planar Si-PEDOT:PSS hybrid solar cells have been demonstrated in this work. Contact-printed, hydrophobically-recovered ultrathin siloxane layer has been employed as insertion layers at interfaces in Si-PEDOT:PSS hybrid solar cells. The printing has been done at room ambient in dry state for 5–10min, which has led to <0.5nm thin siloxane layer at interfaces. The printed ultrathin siloxane plays the role of passivation layer and significantly increases the photocurrent by suppressing charge carrier recombination at interfaces, leading to >13% cell efficiency with non-textured planar Si substrate. Interestingly, the layer has been found to be equally effective at both interfaces (‘top’ interface between Si and PEDOT:PSS, and ‘bottom’ interface between Si and bottom electrode), while other insertion layers suggested in literature works at one interface only. Furthermore, the sheet resistance of PEDOT:PSS layer, rather than resistivity or conductivity, has been found to be the relevant characteristics in the hybrid solar cells, because the carrier conduction in 2-dimension is utmost importance in such devices. The suggested method can be a valuable help for low-cost, high-performance Si-PEDOT:PSS hybrid solar cells and can expedite the commercialization of the hybrid photovoltaics in near future.

High-Efficiency Silicon/Organic Heterojunction Solar Cells with Improved Junction Quality and Interface Passivation.

Silicon/organic heterojunction solar cells (HSCs) based on conjugated polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and n-type silicon (n-Si) have attracted wide attention due to their potential advantages of high efficiency and low cost. However, the state-of-the-art efficiencies are still far from satisfactory due to the inferior junction quality. Here, facile treatments were applied by pretreating the n-Si wafer in tetramethylammonium hydroxide (TMAH) solution and using a capping copper iodide (CuI) layer on the PEDOT:PSS layer to achieve a high-quality Schottky junction. Detailed photoelectric characteristics indicated that the surface recombination was greatly suppressed after TMAH pretreatment, which increased the thickness of the interfacial oxide layer. Furthermore, the CuI capping layer induced a strong inversion layer near the n-Si surface, resulting in an excellent field effect passivation. With the collaborative improvements in the interface chemical and electrical passivation, a competitive open-circuit voltage of 0.656 V and a high fill factor of 78.1% were achieved, leading to a stable efficiency of over 14.3% for the planar n-Si/PEDOT:PSS HSCs. Our findings suggest promising strategies to further exploit the full voltage as well as efficiency potentials for Si/organic solar cells.

A comparative study on the performance of hybrid solar cells containing ZnSTe QDs in hole transporting layer and photoactive layer

In this paper, ZnSTe quantum dots-based hybrid solar cells (HSC) with two different device architectures have been investigated. The improved performance of the poly(3-hexylthiophene) (P3HT) and [6,6]phenyl C71 butyric acid methyl ester (PC71BM)-based bulk heterojunction (BHJ) solar cells by the incorporation of ZnSTe quantum dots (QDs) with an average size of 2.96 nm in PEDOT:PSS layer and active layer that have been demonstrated. Although the efficiency of both types of devices is almost the same, a close comparison reveals different reasons behind their improved performance. The device prepared with QDs in the HTL has shown reduced series resistance, increased shunt resistance, and improved mobility. On the other hand, QDs in the photoactive layer demonstrates increased photo-generation leading to improved efficiency.

Ti/Au Cathode for Electronic transport material-free organic-inorganic hybrid perovskite solar cells.

We have fabricated organic-inorganic hybrid perovskite solar cell that uses a Ti/Au multilayer as cathode and does not use electron transport materials, and achieved the highest power conversion efficiency close to 13% with high reproducibility and hysteresis-free photocurrent curves. Our cell has a Schottky planar heterojunction structure (ITO/PEDOT:PSS/perovskite/Ti/Au), in which the Ti insertion layer isolate the perovskite and Au layers, thus proving good contact between the Au and perovskite and increasing the cells’ shunt resistance greatly. Moreover, the Ti/Au cathode in direct contact with hybrid perovskite showed no reaction for a long-term exposure to the air, and can provide sufficient protection and avoid the perovskite and PEDOT:PSS layers contact with moisture. Hence, the Ti/Au based devices retain about 70% of their original efficiency after 300 h storage in the ambient environment.

Improved Work Function of Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonic acid) and its Effect on Hybrid Silicon/Organic Heterojunction Solar Cells.

Hybrid silicon/organic solar cells have been recently extensively investigated due to their simple structure and low-cost fabrication process. However, the efficiency of the solar cells is greatly limited by the barrier height as well as the carrier recombination at the silicon/organic interface. In this work, hydrochloroplatinic acid (H2PtCl6) is employed into the poly(3,4-ethlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution, and the work function (WF) of the PEDOT:PSS layer has been successfully improved. Based on the Pt-modified PEDOT:PSS layer, the efficiency of the silicon/PEDOT:PSS cell can be increased to 11.46%, corresponding to ~20% enhancement to the one without platinum (Pt) modification. Theoretical and experimental results show that, when increasing the WF of the PEDO:PSS layer, the barrier height between the silicon/PEDOT:PSS interface can be effectively enhanced. Meanwhile, the carrier recombination at the interface is significantly reduced. These results can contribute to better understanding of the interfacial mechanism of silicon/PEDOT:PSS interface, and further improving the device performance of silicon/organic solar cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1759-0) contains supplementary material, which is available to authorized users.

Critical Impact of Hole Transporting Layers and Back Electrode on the Stability of Flexible Organic Photovoltaic Module

Properties of hole transporting layers (HTLs) and back electrode are very critical to the stability of inverted bulk heterojunction organic photovoltaic (OPV) modules. Here, various deposition methods for back electrodes and materials of HTLs are examined by applying to inverted organic solar cells with a structure of indium tin oxide/ZnO/photoactive layer/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Ag. The experiment is performed on encapsulated modules with flexible barrier films under accelerated conditions. The OPV modules with screen‐printed Ag electrodes are shown to be electrically unstable with a reduction of the current density under damp heat condition at 85 °C/85% RH. Optical images for the active layer/PEDOT:PSS interface reveal that a reaction between the solvent from the Ag electrode and the underlying layers is the major cause for the degradation. In comparison with materials of the HTLs, the PEDOT:PSS layer shows low stability compared to the MoO3 layer under the accelerated conditions. Unusual chemical changes in the PEDOT:PSS film are observed through X‐ray photoelectron spectroscopy and this is further addressed by correlating the stability of the OPV devices.

Optical and electrical enhancement for high performance hybrid Si/organic heterojunction solar cells using gold nanoparticles

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layers incorporating with Au nanoparticles (NPs) have been explored for fabricating the hybrid Si/organic solar cells. After incorporating with Au NPs, the power conversation efficiency (PCE) of 12.85% has been achieved, which corresponds to ∼23% improvement comparing with that of the pristine one. The current density-voltage (J-V), external quantum efficiency (EQE), capacitance-voltage (C-V), and transient photovoltage decay (TPV) results demonstrate that, besides the traditional plasmonic effects, the electrical effects caused by Au NPs also contribute to the enhancement of the device performance. After incorporating with Au NPs, the conductivity of the PEDOT:PSS layer is slightly enhanced and the built-in electric field (Vbi) of the device is also improved. Both of them are also beneficial for enhanced charge separation and collection, significantly suppressing the recombination process of the devices. Our preliminary results highlight the importance that both optical and electrical properties need to be addressed simultaneously for achieving high PCEs, which give a path to enhance the performance of the Si/organic solar cells with metallic NPs.

Nafion-Modified PEDOT:PSS as a Transparent Hole-Transporting Layer for High-Performance Crystalline-Si/Organic Heterojunction Solar Cells with Improved Light Soaking Stability.

We demonstrate the chemistry of amphiphilic perfluorosulfonic copolymer Nafion-coated conductive poly(3,4-ethyelenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and its effect on the photovoltaic performance of PEDOT:PSS/crystalline Si (c-Si) heterojunction solar cells. The highly hydrophilic sulfonate group of insulating, chemically stable Nafion interacts with PSS in PEDOT:PSS, which reduce the Coulombic interaction between PEDOT and PSS. The highly hydrophobic fluorocarbon backbone of Nafion favorably interacts with hydrophobic PEDOT of PEDOT:PSS. These factors give rise to the extension of π-conjugation of PEDOT chains. Silver paste used as a top grid electrode diffused into the Nafion layer and contacted with underneath Nafion-modified PEDOT:PSS layer. As a consequent, solution-processed Nafion-coated PEDOT:PSS/c-Si heterojunction solar cells exhibited a higher power conversion efficiency of 14.0% with better stability for light soaking rather than that of the pristine PEDOT:PSS/c-Si device by adjusting the layer thickness of Nafion. These findings originate from the chemical stability of hydrophobic fluorocarbon backbone of Nafion, diffusivity of silver paste into Nafion and contact with PEDOT:PSS, and Nafion as an antireflection layer.

Efficient PbS QD solar cell with an inverted structure

Efficient PbS quantum dot (QD) solar cell with the traditional structure requires an inorganic buffer layer that is usually fabricated at high temperature, which is not compatible with the industrially preferential roll-to-roll fabrication process. Identification of a suitable buffer layer and efficient device construction are thus of particular significance. Herein, we fabricate PbS quantum dot solar cells in an inverted structure using poly(thiophene) (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) as the anode buffer layer. The resulting devices present a high efficiency of 4.1%, among the best values of inverted PbS QD solar cells. Electrochemical and photoelectric characterizations have shown that, compared with high-temperature annealed nickel oxide (NiO) and vanadium pentoxide (V2O5) layers, the low-temperature processed PEDOT:PSS layer has a more compatible film properties for efficient injection and collection of charges from PbS QD active layer. Our work provides a promising strategy for fabrication of QD solar cells in an economical and efficient way.

Modified PEDOT Layer Makes a 1.52 V Voc for Perovskite/PCBM Solar Cells

The work functions for charge transport layers in perovskite solar cells affect device performance significantly. In this work, the regular poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is modified by adding a polymer electrolyte PSS‐Na to improve its HTL function in perovskite solar cells. The modified PEDOT:PSS films (called m‐PEDOT:PSS) possess higher work function than the regular one. Its energy level matches the valence band of perovskite very well, leading to enhanced Voc and PCE (power conversion efficiency). When CH3NH3PbI3 is used as the light absorber, the cell with PEDOT:PSS HTL gives a Voc of 0.96 V and a PCE of 12.35%, while the cell with m‐PEDOT:PSS layer gives a Voc of 1.11 V and a PCE of 15.56%. Enhanced Voc and PCE are also achieved when CH3NH3PbI2Br or CH3NH3PbBr3 is used as the light absorber. The m‐PEDOT:PSS/CH3NH3PbBr3/PC61BM solar cells demonstrate an outstanding Voc of 1.52 V.

Ultrathin organic spin-on layers on indium tin oxide as a prospective tool for enhanced light throughput

Organic layers coated on ITO-glass substrates have widespread applications in many optoelectronic devices and displays. Here, we report certain organic/polymer ultrathin layers could boost optical transmittance by 10–15% in a wavelength range that strongly depends on the layer thickness. Studies with normal incidence reflection spectroscopy suggest towards the formation of an antireflection (AR) layer whenever film refractive index requirement is satisfied. Additionally, these film layers reduce scattering loss from the substrate surface that further improves the clarity. Using spin-coated PEDOT:PSS layers with varying spin speeds, we showed that thickness assessment of such layers with lower surface roughness's are possible from the antireflection principles. In the 350–800nm wavelength range, use of certain polymer layers could result in ~4–6% gain in the photon influx that could be functional in the optoelectronic devices.

Anisotropic thin films formation rate on PEDOT : PSS layer with high azimuthal anchoring

AbstractOriented organic layers have great potential for organic electronics devices because of the unique modification of material properties without extensive chemical synthesis. Such layers can be prepared by wet coating of anisotropic organic molecules on top of specific surface of alignment layer. One of the most important parameter that indicates alignment properties of the surface is the anchoring energy. In this paper, we investigate azimuthal anchoring energy of pure and glycerol‐doped PEDOT : PSS layers and study the influence of the alignment layer preparation on the order parameter of the top wet‐coated oriented organic emitter. We confirm that the azimuthal anchoring energy increase leads to improvement of both dichroic ratio and contrast ratio of polarized emitter layer rod‐coated on top of the PEDOT : PSS. Suggested mechanism of anisotropic emitter formation at wet deposition grounds possibility of linear deposition rate of 2 m/s on top of PEDOT : PSS layer with obtained azimuthal anchoring above &gt;10−4 J/m2.

The Study of Optical and Electrical Properties of Solar Cells With Oblique Incidence

The optical and electrical properties of organic solar cells with metallic Ag incorporating into the PEDOT:PSS layer in the case of oblique incidence are numerically investigated based on in house finite-difference frequency-domain code. It is found that the light absorption decreases with the increase of incident angle, and the absorption enhancement varies slightly due to the contribution of the broadband surface plasmon (SP)-mode. Since the absorption reduces at large incident angle, the short-circuit current undoubtedly decreases, thus fill factor and power conversion efficiency reduce accordingly. However, there is little variety of open-circuit voltage, which indicates that open-circuit voltage is independent of incident angle. Our results can be used as a reference for better understanding of the optical and electrical properties of organic solar cells with oblique incidence.

Investigation of silver nanowires with a PEDOT:PSS layer for haze reduction

Silver nanowires (AgNWs) are often used as transparent electrodes because they contribute sheet resistance and mechanical flexibility to the electrodes. However, the optical haze still needs to be improved in order for AgNWs to be suitable for display applications. In this study, we investigated the optimal structure of AgNW films with a capping layer for reducing haze. We investigated the haze of AgNWs covered by poly (3, 4-ethylenedioxithiophene):poly (styrenesulfonate) (PEDOT:PSS) and/or indium tin oxide (ITO), which were simulated to investigate the reduction of haze in the visible spectrum. A finite-difference time-domain (FDTD) simulation showed that optimized Ag- NWs with an insulating capping layer showed less optical haze than AgNW films alone. The haze reduction was 6 % maximum for a AgNW with a radius of 70 nm with 20-nm-thick PEDOT:PSS added. Also, a haze reduction of 0.7 % was achieved by adding the surrounding PEDOT:PSS with a thickness of 20 nm, and one of 0.3 % was achieved as the thickness of PEDOT:PSS was increased from 20 nm to 60 nm when the radius of the AgNW was fixed at 20 nm. From the simulation results, we confirmed that the capping layer was responsible for the haze reduction.

Grain structure control and greatly enhanced carrier transport by CH3NH3PbCl3 interlayer in two-step solution processed planar perovskite solar cells

We report that the use of a CH3NH3PbCl3 interlayer onto the PEDOT:PSS layer in the two-step solution deposition of CH3NH3Pbl3 for planar p-i-n type perovskite solar cells (PSCs) can lead to a dramatic enhancement of short-circuit current density (Jsc) by 52.8% from 13.07 mA cm−2 to 19.98 mA cm−2. While the absorption and thus the composition of the perovskite layers remain unchanged, Incident photon-to-current efficiency (IPCE) measurement results reveal much enhanced carrier transport, which in turn can be correlated to the larger and more columnar grain structure in the perovskite layer with the use of the CH3NH3PbCl3 interlayer. On the other hand, the two-step solution processed perovskite layers without the CH3NH3PbCl3 interlayer exhibit smaller and more cross-hatching grain structure and yield significantly smaller Jsc. Therefore our results revealed clearly that the insertion of CH3NH3PbCl3 interlayer, which affects the nucleation dynamics, may control the grain structure of the two-step solution processed perovskite layers and improve dramatically the photovoltaic performance of the resultant planar p-i-n type PSCs. Our CH3NH3PbCl3 interlayer may thus serve as an effective method for p-i-n PSCs to achieve high Jsc with thicker perovskite layer.