PSS Heterojunction Research Articles

Planar Organic‐Si Hybrid Solar Cell with MoOx Mixed PEDOT:PSS as Hole Injection Layer Profits from Mo5+ and Mo6+ Synergistic Effects

AbstractPoly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layer plays an important role in planar Si/PEDOT:PSS heterojunction solar cells (HSCs). Herein, a MoOx mixed aqueous PEDOT:PSS cosolvent is developed and is applied into a Si/PEDOT:PSS solar cell preparation via a time‐saving one‐step spin‐coating method. With an optimal concentration of MoOx dopants, the power conversion efficiency of the device exhibits from 10.26% up to 13.82% with all inherent photovoltaic parameters enhanced. The detailed characterization and analytical results indicate that an advanced electronic property is produced by MoOx dopants and interface optimization caused by synergistic effects from Mo5+ and Mo6+ species with PEDOT:PSS, which enhances its interface work function and promotes hole transportation capacity. The result paves a path for exploring efficient Si/PEDOT:PSS HSCs with suitable functional material and a simple solution‐processable method.

Effect of interfacial passivation on inverted pyramid silicon/poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) heterojunction solar cells

The poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and inverted pyramid n-silicon heterojunction solar cells have been extensively investigated based on their light trapping behaviour, rationally high efficiency and cost effectiveness. However, inferior junction conformity still remains a great challenge. In this work, we present the effect of passivation using aluminium oxide (Al2O3) on the front surface and titanium oxide (TiO2) on rear interface in the inverted pyramid -Si/PEDOT: PSS heterojunction solar cells using the atomic layer deposition technique. The front surface Al2O3 layer can enhance the surface energy, which generates the uniform coating of PEDOT:PSS, acting as an electron blocking layer. Furthermore, TiO2 thin layer deposited on rear interface works as a hole blocking layer, which can suppress the electrical losses and the charge recombination. The best cell demonstrated a conversion efficiency of 16.04% with an open-circuit voltage of 0.63 V, fill factor of 71.5% and a high current density of 35.45 mA/cm2. These findings suggest a promising approach to attainment of next-generation hybrid solar cells.

An in situ rewritable electrically-erasable photo-memory device for terahertz waves.

A terahertz read-only in situ electrically-erasable rewritable photo-memory device based on a perovskite:Ag (perovskite with Ag nanoparticles added)/SnO2/PEDOT:PSS hetero-junction structure is reported. Under low optical excitation, considerable terahertz amplitude modulation in a perovskite:Ag/PEDOT:PSS hybrid structure was achieved. When a SnO2 nanoparticle film was inserted between the perovskite and PEDOT:PSS layer, the attenuation of the terahertz signal was weaker than that of the perovskite:Ag/PEDOT:PSS hybrid structure; however, the SnO2 nanoparticle film considerably prolonged the recovery time of the modulated terahertz wave in air after photo-excitation was stopped. In addition, when bias voltages were applied to the perovskite:Ag/PEDOT:PSS and perovskite:Ag/SnO2/PEDOT:PSS hybrid structures, respectively, the terahertz signals recovered rapidly for both structures. Consequently, the photo-memory functionality was achieved based on a perovskite:Ag/SnO2/PEDOT:PSS hybrid structure with an in situ method for erasing stored information.

Optimization of SnO2-based electron-selective contacts for Si/PEDOT:PSS heterojunction solar cells

Tin oxide (SnO2) is a potentially excellent electron-selective contact (ESC) for silicon (Si)-based solar cells due to its satisfactory energy band structure and good crystallinity. However, unsatisfactory electron extraction ability and limited surface passivating effect of SnO2 ESCs will limit the performance of corresponding solar cells. We increase the Fermi level of SnO2 by doping Ethylene diamine tetraacetic acid (EDTA), which endows EDTA-SnO2 better electron extraction ability than SnO2. Moreover, EDTA-SnO2/SiOx bilayer ESC prepared by combining a EDTA-SnO2 layer and a thin silicon oxide (SiOx) film provides better surface passivation than EDTA-SnO2 ESC without impairing the charge transport capability markedly. The planar Si/PEDOT:PSS heterojunction solar cells (HSCs) with EDTA-SnO2/SiOx bilayer ESCs exhibit a power conversion efficiency (η) of 11.52%, which improves 13.7% in comparison with the η (10.13%) of HSCs with SnO2 ESCs, mainly caused by the increase in Voc and FF by 18 mV and 5.4% respectively.

Nanostructural and barrier property characterization of ZnO/PEDOT:PSS heterojunction by adjusting RF power in the magnetron sputtering deposition technique

Nanostructure and barrier properties of the heterojunction formed at the interface of ZnO/PEDOT:PSS inorganic/organic contact have been investigated. The PEDOT:PSS layer and the zinc oxide nanostructures have been deposited using the spin coating and the radio frequency magnetron sputtering techniques on glass substrates at room temperature, respectively. Particularly, the effects of zinc oxide sputtering power on the nanostructure properties of the deposited layer are investigated. The deposition power varies from 60 to 240 W. AFM results show that increasing the deposition power, results in the grain size and the surface roughness of the zinc oxide layer to increase. The energy gap measured for the zinc oxide layers deposited at the powers of 60, 120, 180 and 240 W was 3.24, 3.23, 3.18, and 3.20 eV, respectively. In order to investigate the heterojunction formed at the interface of zinc oxide and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), a polymeric layer of thickness of 50 nm is deposited on a 300-nm zinc oxide layer. The dark I–V characteristics indicate that the reverse saturation current density is 5.01 × 10−7, 3.16 × 10−5, 1.96 × 10−7 and 7.98 × 10−7 A/cm2 for the deposition power of 60, 120, 180, and 240 W, respectively. By increasing the deposition power the ideality factor of the resulting Schottky barrier is 3.2, 2.9, 2.3 and 3.6. The effective Schottky barrier heights of 0.76, 0.77, 0.78, and 0.75 eV were obtained for the same order of deposition powers. It was found that the highest optical response could be obtained for the samples prepared at the deposition power of 180 W.

Schottky diode based resistive switching device based on ZnO/PEDOT:PSS heterojunction to reduce sneak current problem

To realize an asymmetric function blockable sneak currents in the resistive switching memory device, we propose a novel schottky diode based high charge density resistive switching device based on zinc oxide (ZnO) and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) heterojunction, which is structured with bottom and top electrode as indium tin oxide (ITO) and silver (Ag), respectively. The heterojunction layers are deposited through a spin coater on ITO coated polyethylene terephthalate (PET) substrate. The hetrojunction resistive switching device is measured over more than 500 endurance cycles on dual polarity voltage of ± 3 V. The stability of the memory device is analyzed for more than 30 days with high resistance state (HRS) and low resistance state (LRS) as 531047870.8 Ω and 1001636.011 Ω, respectively, at reading voltage of 1.28 V in forward current, and its Roff/Ron ratio is recorded as ~ 530. In reverse current, the HRS ~ 153081392.6 Ω and LRS ~ 19034020.25 Ω are recorded at voltage read of ~ − 1.28 V and they are both high resistance as its Roff/Ron ratio is ~ 8.04. This asymmetric function insures that the proposed memory device helps to reduce the sneak current. Hence, it can be applied in flexible resistive switching devices to blocking sneak current problem.

14.1% efficiency hybrid planar-Si/organic heterojunction solar cells with SnO2 insertion layer

Hybrid planar-Si/organic heterojunction solar cells have gained considerable interest in the fabrication of cost-effective and high-efficiency devices. However, most of high power conversion efficiency (PCE) performances have been obtained with particular structures, front surface texture or rear surface field layer. In this paper, we provide a simple method without complex structures, and demonstrate the superiority and the mechanism of using stannic oxide (SnO2) as an insertion layer. The SnO2 insertion layer takes the place of the Schottky barrier, which reduces barrier height of rear Si to enhance charge transfer. And the effect of the insertion layer reduces contact resistance and enhances contact quality of rear Si side. Meanwhile, it has been indicated that the Si-O-Sn bonds were formed by SnO2 and Si dangling bond (Si-), which have a passivation effect on the Si surface to effectively suppress the recombination losses. Furthermore, simulations using density functional theory (DFT) confirm that the electrostatic potential can improve electronic transmission from Si to Sn between Si-O-Sn bonds. Finally, for the hybrid planar-Si/PEDOT:PSS heterojunction solar cells without any special structures, the highest PCE of 14.1% was achieved, up 10.8% compared with that without SnO2 insertion layer. These findings provide an effective way of improving Si/metal contact via a simple, room temperature process for other photovoltaic devices.

Buried MoO x/Ag Electrode Enables High-Efficiency Organic/Silicon Heterojunction Solar Cells with a High Fill Factor.

Silicon (Si)/organic heterojunction solar cells based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n-type Si have attracted wide interests because they promise cost-effectiveness and high-efficiency. However, the limited conductivity of PEDOT:PSS leads to an inefficient hole transport efficiency for the heterojunction device. Therefore, a high dense top-contact metal grid electrode is required to assure the efficient charge collection efficiency. Unfortunately, the large metal grid coverage ratio electrode would lead to undesirable optical loss. Here, we develop a strategy to balance PEDOT:PSS conductivity and grid optical transmittance via a buried molybdenum oxide/silver grid electrode. In addition, the grid electrode coverage ratio is optimized to reduce its light shading effect. The buried electrode dramatically reduces the device series resistance, which leads to a higher fill factor (FF). With the optimized buried electrode, a record FF of 80% is achieved for flat Si/PEDOT:PSS heterojunction devices. With further enhancement adhesion between the PEDOT:PSS film and Si substrate by a chemical cross-linkable silance, a power conversion efficiency of 16.3% for organic/textured Si heterojunction devices is achieved. Our results provide a path to overcome the inferior organic semiconductor property to enhance the organic/Si heterojunction solar cell.

High‐Performance Organic‐Silicon Heterojunction Solar Cells by Using Al‐Doped ZnO as Cathode Interlayer

Organic‐silicon heterojunction solar cells have recently emerged as a promising photovoltaic technique with the attractiveness of good performance and ease of processing. However, the poor collection property of electrons in cathodic interface is one of the most critical problems to be solved. In this study, a novel application of solution‐processed inorganic semiconductor nanocrystals of aluminum‐doped zinc oxide (AZO) is presented as cathode interlayer between the n‐type silicon (n‐Si) and rear aluminum (Al) electrode. With appropriate annealing temperature and doping concentration, the contact of n‐Si/AZO/Al exhibits a resistivity as low as 3 mΩ cm−2. It is found that annealing the spin‐coated AZO solution at 200 °C is benefit to both formation of uniform film and sufficient replacement Zn atoms with Al atoms. Chemical structure investigations reveal the existence of AlOSi bonds at the interface, which may help to reduce the dangling bonds of n‐Si and deliver improved passivation. These AZO thin films are successfully used in planar n‐Si/PEDOT:PSS heterojunction solar cells as efficient electron‐selective layers, rendering a 10% relative increase in efficiency over the reference cells (13.6 over 12.3%). Our finding fully demonstrates its promising potential of this low‐temperature solution‐processed AZO interlayer for applications not only in hybrid solar cells but also in other types of silicon‐based photovoltaic devices.

P‐115: Distinguished Student Paper: All Solution‐Processed White Quantum‐Dot Light‐Emitting Diodes with Three‐Unit Tandem Structure

In this work, we demonstrate all‐solution processed three‐unit (red/green/blue) white tandem QLEDs for the first time. The white tandem devices are achieved by serially connecting the red bottom sub‐QLED, the green middle sub‐QLED and the blue top sub QLED using the inter‐connecting layer (ICL) based on ZnMgO/PEDOT:PSS heterojunction. With the proposed ICL, the two‐unit tandem QLEDs exhibit a high current efficiency of 22.22 cd/A, while the three‐unit white QLEDs exhibit a peak current efficiency of 4.75 cd/A at a high luminance of 4206 cd/m2 . Displays based on the developed white QLEDs exhibit a wide color gamut of 114% NTSC. This work confirms the effectiveness of the proposed ZnMgO/PEDOT:PSS ICL and the feasibility of making all‐solution processed tandem white QLEDs by using the proposed ICL.

All solution‐processed white quantum‐dot light‐emitting diodes with three‐unit tandem structure

AbstractQuantum‐dot light‐emitting diodes (QLEDs) are promising candidates for next generation displays. White QLEDs which can emit red, green and blue colors are particularly important; this is because the combination of white QLEDs and color filters offers a practical solution for high‐resolution full‐color displays. In this work, we demonstrate all‐solution processed three‐unit (red/green/blue) white tandem QLEDs for the first time. The white tandem devices are achieved by serially connecting the red bottom sub‐QLED, the green middle sub‐QLED and the blue top sub‐QLED using the inter‐connecting layer (ICL) based on ZnMgO/PEDOT:PSS heterojunction. With the proposed ICL, the two‐unit tandem QLEDs exhibit a high current efficiency of 22.22 cd/A, while the three‐unit white QLEDs exhibit evenly separated red, green and blue emission with a CIE coordinate of (0.30, 0.44), a peak current efficiency of 4.75 cd/A and a high luminance of 4206 cd/m2. Displays based on the developed white QLEDs exhibit a wide color gamut of 114% NTSC. This work confirms the effectiveness of the proposed ZnMgO/PEDOT:PSS ICL and the feasibility of making all‐solution processed tandem white QLEDs by using the proposed ICL.

Silicon/Organic Heterojunction for Photoelectrochemical Energy Conversion Photoanode with a Record Photovoltage.

Silicon (Si) is a good photon absorption material for photoelectrochemical (PEC) conversion. Recently, the relatively low photovoltage of Si-based PEC anode is one of the most significant factors limiting its performance. To achieve a high photovoltage in PEC electrode, both a large barrier height and high-quality surface passivation of Si are indispensable. However, it is still challenging to induce a large band bending and passivate Si surface simultaneously in Si-based PEC photoanodes so far, which hinders their performance. Here, we develop a simple Si/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) heterojunction with large band banding and excellent surface passiviation for efficient PEC conversion. A chemically modified PEDOT:PSS film acts as both a surface passiviation layer and an effective catalyst simultaneously without sacrificing band bending level. A record photovoltage for Si-based PEC photoanodes as high as 657 mV is achieved via optimizing the PEDOT:PSS film fabrication process. The density of electron state (DOS) measurement is utilized to probe the passivation quality of the organic/inorganic heterojunction, and a low DOS is found in the Si/PEDOT:PSS heterojunction, which is in accordance with the photovoltage results. The low-temperature solution-processed Si/organic heterojunction photoanode provides a high photovoltage, exhibiting the potential to be the next-generation economical photoanode in PEC applications.

Effect of substrate bias on mist deposition of conjugated polymer on textured crystalline‐Si for efficient c‐Si/organic heterojunction solar cells

We investigated the chemical mist deposition (CMD) of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on textured crystalline silicon (c‐Si) substrate for efficient c‐Si/PEDOT:PSS heterojunction solar cells. The Mie scattering observation and differential mobility analysis characterization revealed that the average size of mist particle decreased from 330 to 30–40 nm with increasing the number density and traveling velocity of mist precursor when positive dc bias of 10 kV was applied to the c‐Si substrate. The uniform deposition of PEDOT:PSS films was performed on textured c‐Si with the increased adhesion by suitably adjusting Vs and substrate temperature. A power conversion efficiency (PCE) of 11.57% was obtained with Jsc of 36.1 mA cm−2, Voc of 0.49 V, and FF of 0.66, when a positive Vs of 10 kV was applied to c‐Si substrate. Furthermore, PCE increased to 12.5% with Jsc of 35.6 mA cm−2, Voc of 0.53 V, and FF of 0.67 by adding a 20‐nm‐thick AR coating layer of molybdenum oxide MoOx (refractive index, n = 2.1) fabricated by CMD using 12 molybdo(VI) phosphoric acid n‐hydrate [H3(PMo12O40) · nH2O] as a precursor. These findings imply that CMD using negatively charged mist precursor is a possible method for the uniform deposition of PEDOT:PSS on textured c‐Si substrate for efficient c‐Si/PEDOT:PSS heterojunction solar cells.

Junction formation and current transport mechanisms in hybrid n-Si/PEDOT:PSS solar cells.

We investigated hybrid inorganic-organic solar cells combining monocrystalline n-type silicon (n-Si) and a highly conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). The build-in potential, photo- and dark saturation current at this hybrid interface are monitored for varying n-Si doping concentrations. We corroborate that a high build-in potential forms at the hybrid junction leading to strong inversion of the n-Si surface. By extracting work function and valence band edge of the polymer from ultraviolet photoelectron spectroscopy, a band diagram of the hybrid n-Si/PEDOT:PSS heterojunction is presented. The current-voltage characteristics were analyzed using Schottky and abrupt pn-junction models. The magnitude as well as the dependence of dark saturation current on n-Si doping concentration proves that the transport is governed by diffusion of minority charge carriers in the n-Si and not by thermionic emission of majorities over a Schottky barrier. This leads to a comprehensive explanation of the high observed open-circuit voltages of up to 634 mV connected to high conversion efficiency of almost 14%, even for simple planar device structures without antireflection coating or optimized contacts. The presented work clearly shows that PEDOT:PSS forms a hybrid heterojunction with n-Si behaving similar to a conventional pn-junction and not, like commonly assumed, a Schottky junction.

Electrical and photoelectrochemical characteristics of flexible CdS nanocomposite/conducting polymer heterojunction

The electrical properties of CdS-polyvinyl alcohol (CdS-PVA) nanocomposites have been investigated in details. The junction behavior of CdS-PVA and a conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) heterojunction have been studied. The current–voltage characteristics of the nanocomposite samples have also performed at different bending angles. The bending study has been carried out after deposition of CdS-PVA and CdS-PVA/PEDOT:PSS heterojunction films on indium tin oxide coated (ITO) flexible polyethylene terephthalate (PET) substrates. Spectral dependent photoconductive properties of the nanocomposite-polymer heterojunctions have been investigated. The electrochemical photosensing behaviors have been demonstrated using CdS-PVA nanocomposites and CdS-PVA/PEDOT:PSS heterojunction films as photoanodes.

Characteristics of a silicon nanowires/PEDOT:PSS heterojunction and its effect on the solar cell performance.

The interfacial energy-level alignment of a silicon nanowires (SiNWs)/PEDOT:PSS heterojunction is investigated using Kelvin probe force microscopy. The potential difference and electrical distribution in the junction are systematically revealed. When the PEDOT:PSS layer is covered at the bottom of the SiNW array, an abrupt junction is formed at the interface whose characteristics are mainly determined by the uniformly doped Si bulk. When the PEDOT:PSS layer is covered on the top, a hyperabrupt junction localized at the top of the SiNWs forms, and this characteristic depends on the surface properties of the SiNWs. Because the calculation shows that the absorption of light from the SiNWs and the Si bulk are equally important, the bottom-coverage structure leads to better position matching between the depletion and absorption area and therefore shows better photovoltaic performance. The dependence of JSC and VOC on the junction characteristic is discussed.

Organic/inorganic heterojunction based on conducting polymer and pulse-laser-deposited (PLD) ZnO

ABSTRACTOrganic/inorganic heterojunctions have been fabricated by spin coating p-type poly (3, 4 ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) onto n-type zinc oxide (ZnO) films. The ZnO films were deposited onto indium tin oxide (ITO) coated glass by pulse laser deposition (PLD) technique. The current density-voltage (J-V) characteristics of the PLD-ZnO/PEDOT:PSS junction based on as-deposited PLD-ZnO film shows a good rectifying behavior with a rectification ratio of 156 at ±1 V, indicating the formation of a diode between ZnO and PEDOT:PSS. Using thermionic emission model, the ideality factor (n=2.1) and barrier height (0.66 eV) of the heterojunction were obtained. Those diode parameters are better than those of the chemical vapor deposited ZnO/PEDOT:PSS heterojunction reported elsewhere, indicating that PLD may be a promising technique on fabricating high quality ZnO/polymer heterojunctions.

Electroluminescence of ZnO nanorods embedded in a polymer film

Vertically aligned ZnO nanorods (NRs) were grown on a ZnO film and embedded in the poly(3,4 ethyle-nedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to fabricate a ZnO film/ZnO nanorods/polymer hybrid structured light emitting diode (LED). The embedded ZnO NRs can increase the injected current of the ZnO/PEDOT:PSS heterojunction and play key roles in the emission process. We demonstrate the ZnO NRs are the radiative recombination zone in the LED. Electroluminescence (EL) spectrum of the hybrid LED consists of one ultraviolet (UV) near-band-edge emission peak and two visible deep-level emission peaks. The relative intensities of the three peaks are evidently influenced by the applied voltage, which can be clearly explained by the energy band diagram.

Optical anisotropy in solvent-modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) and its effect on the photovoltaic performance of crystalline silicon/organic heterojunction solar cells

An investigation was carried out into the effect of uniaxial optical anisotropy in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) on the photovoltaic performance of crystalline Si/PEDOT:PSS heterojunction solar cells fabricated by spin coating using either a methanol (MeOH) solvent alone or using MeOH and ethylene glycol (EG) as cosolvents. Spectroscopic ellipsometry revealed that the extraordinary index of refraction increased by the use of the cosolvents. In contrast, the ordinary index of refraction indicated metallic properties and was almost independent of the concentration of MeOH or EG. The highest conductivity was found for a (PEDOT:PSS):(MeOH):(EG) weight ratio of 1:1:0.1, and this sample exhibited a relatively high power conversion efficiency of 11.23%. These findings suggest that the increase in the extraordinary index of refraction leads to an enhancement of the hole mobility in PEDOT:PSS, resulting in improved photovoltaic performance.

Effects of molybdenum oxide molecular doping on the chemical structure of poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) and on carrier collection efficiency of silicon/poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) heterojunction solar cells

The effects of MoO3 molecular doping in poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) (PEDOT:PSS) on the chemical structure and, in turn, on the carrier collection efficiency of c-Si/PEDOT:PSS heterojunction solar cells are demonstrated. Scanning electron microscopy revealed that the hydrophilic PSS polymer chain was intercalated into the interlayer van der Waals gap of MoO3 flake sheets, which modified the chemical structure of PEDOT:PSS. MoO3 exhibited intense photoluminescence in the 350–550 nm region, which enhanced the carrier collection efficiency of c-Si/PEDOT:PSS heterojunction solar cells with no significant changes. These findings suggest that the intense photoluminescence of MoO3 and its light wavelength conversion contribute to the increased carrier collection efficiency.