Influence of n-type chemical doping layer on the performance of organic photovoltaic solar cells

We report the performance improvement of organic solar cell by addition of an n-type chemical doping layer in organic bulk heterojunction device. The power conversion efficiency (PCE) of P3HT and PCBM-71 based polymer solar cells increases by adding a mixture of TCNQ (7,7,8,8-tetracyanoquinodimethane) and LCV (Leucocrystal violet) between active layer and cathode electrode. The PCE of the cell increases by 14% compared to the control cell with Al-only cathode electrode. The device with an organic n-doped layer shows the J_SC of 8.88 mA/cm², V_OC of 0.51 V, FF of 60.1%, and thus the PCE of 2.72% under AM1.5 illumination of 100 mW/cm².     

Air-stable triarylamine-based amorphous polymer as donor material for bulk-heterojunction organic solar cells

A new air-stable triarylamine-based amorphous polymer, TSP-T11, which consists of thiophene and triarylamine units, can be successfully utilized to fabricate bulk-heterojunction organic photovoltaics (OPVs) using PC₆₀BM or PC₇₀BM as acceptor materials. The highest level of performance of OPVs optimized at TSP-T11:PC₇₀BM (weight ratios of 1:4) with thicknesses of 68 nm exhibited an open circuit voltage (V_oc) of 0.75 V, a short circuit current (J_sc) of 8.03 mA cm⁻², and a power-conversion efficiency (PCE) of 2.22% under simulated air mass 1.5 solar irradiation at 100 mW cm⁻². Although TSP-T11 has a lower hole mobility (1.5×10⁻⁴ cm² V⁻¹ s⁻¹) than P3HT, the use of amorphous film of TSP-T11 as a donor material for OPVs offers advantages over the use of polycrystalline film of P3HT in terms of its air-stability and pinhole-free homogeneous morphology.     

Improving the efficiency of organic solar cell with a novel ambipolar polymer to form ternary cascade structure

This study describes the utilization of a novel conjugated copolymer, namely, poly[2,3-bis(thiophen-2-yl)-acrylonitrile-9,9′-dioctyl-fluorene] (FLC8) for organic solar cell application for the first time. The highest occupied molecular orbital and the lowest unoccupied molecular orbital of FLC8 are −5.68 and −3.55 eV, respectively, which lie between the corresponding values of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methylester (PCBM). In addition, both electron and hole mobilities of FLC8 are in the range of 10⁻⁴ (cm²/V s), making it an excellent ambipolar polymer. Such unique properties make FLC8 a good candidate to form a ternary cascade bulk-heterojunction organic solar cell when blending with P3HT and PCBM. The power conversion efficiency (PCE) of the ternary cascade solar cell can be increased by up to 30% as compared with the reference cell without FLC8. We suspect that this enhancement of PCE is caused by the additional charge separation offered by the cascade structure and the fast charge transfer due to the ambipolarity of FLC8.     

Ultra low Pt-loading electrode prepared by displacement of electrodeposited Cu particles on a porous carbon electrode

Ultra low Pt-loading and high Pt utilization electrodes were prepared by displacement of electrodeposited Cu on a porous carbon electrode. Copper particles were electrodeposited on a porous carbon electrode (PCE) by four-step deposition (FSD) at first. The size and dispersion of deposited Cu particles were markedly improved with application of the FSD. The Cu deposits were then displaced by platinum as dipping a Cu/PCE in a platinum salt solution. Sequentially, Pt particles supported on the PCE were obtained. The Pt/PCE electrode prepared via the FSD of Cu overcomes the problem of the hydrogen evolution reaction accompanied with direct platinum electrochemical deposition, and has a high Pt dispersion. The single cell consisting of the electrodes Pt/PCE via the FSD of Cu outputs a power of 0.45 W cm⁻² with ultra low Pt loadings of 0.196 mg cm⁻² MEA (0.098 mg cm⁻² per each side of the MEA) at no backpressure of reactant gases.     

Efficiency enhancement of polymer solar cells by incorporating a self-assembled layer of silver nanodisks

We report the efficiency enhancement of polymer solar cells by incorporating a silver nanodisks' self-assembled layer, which was grown on the indium tin oxide (ITO) surface by the electrostatic interaction between the silver particles and modified ITO. Polymer solar cells with a structure of ITO (with silver nanodisks)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) (Clevious P VP AI 4083)/poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PC₆₁BM)/LiF/Al exhibited an open circuit voltage (V_OC) of 0.61±0.01 V, short-circuit current density (J_SC) of 9.24±0.09 mA/cm², a fill factor (FF) of 0.60±0.01, and power conversion efficiency (PCE) of 3.46±0.07% under one sun of simulated air mass 1.5 global (AM1.5G) irradiation (100 mW/cm²). The PCE was increased from 2.72±0.08% of the devices without silver nanodisks to 3.46±0.07%, mainly from the improved photocurrent density as a result of the excited localized surface plasmon resonance (LSPR) induced by the silver nanodisks.     

Platinum-sputtered electrode based on blend of carbon nanotubes and carbon black for polymer electrolyte fuel cell

A novel Pt-sputtered electrode based on a blend layer of carbon black (CB) and carbon nanotubes (CNTs) is developed for polymer electrolyte fuel cells. The Pt is sputtered on the surface of the blend to form a catalyst layer. The CNTs generate a pore in the blend layer, and the CB provides a high surface roughness for the blend layer. At a CNT content of 50 wt.%, the maximum value (20.6 m² g⁻¹) for the electrochemical area of the Pt is obtained, which indicates that the surface area of the blend layer exposed for Pt deposition is the largest. The power density of a membrane-electrode assembly (MEA) employing the Pt-sputtered electrodes shows a linear increase with electrochemical area. The mass activity of the optimized Pt-sputtered electrode with a Pt loading of 0.05 mg cm⁻² is 8.1 times that of an electrode with a Pt loading of 0.5 mg cm⁻² prepared using a conventional screen-printing technique. Excellent mass transfer is obtained with the Pt-sputtered electrode.     

A plate-frame flow-through microfluidic fuel cell stack

We present a plate-frame microfluidic fuel cell architecture with porous flow-through electrodes. The architecture combines the advantages of recent microfluidic fuel cells with those of traditional plate-frame PEM fuel cells and enables vertical stacking with little dead volume. Peak current and power densities of 15.7 mA cm⁻² and 5.8 mW cm⁻² were observed. In addition to the new plate-frame architecture, microfabrication techniques have been used to create a new form of high performance electrode. Laser ablation of a polymer precursor followed by a pyrolysis process was used to create a thin, low-cost micro-porous electrode that provides for more rapid reactant transport. Here we show a 140% increase in power density compared to commercial carbon fiber paper.     

Performance of an ultra-low platinum loading membrane electrode assembly prepared by a novel catalyst-sprayed membrane technique

Membrane electrode assemblies (MEAs) with ultra-low platinum loadings are attracting significant attention as one method of reducing the quantity of precious metal in polymer electrolyte membrane fuel cells (PEMFCs) and thereby decreasing their cost, one of the key obstacles to the commercialization of PEMFCs. In the present work, high-performance MEAs with ultra-low platinum loadings are developed using a novel catalyst-sprayed membrane technique. The platinum loadings of the anode and cathode are lowered to 0.04 and 0.12 mg cm⁻², respectively, but still yield a high performance of 0.7 A cm⁻² at 0.7 V. The influence of Nafion content, cell temperature, and back pressures of the reactant gases are investigated. The optimal Nafion content in the catalyst layer is ca. 25 wt.%. This is significantly lower than for low platinum loading MEAs prepared by other methods, indicating ample interfacial contact between the catalyst layer and membrane in our prepared MEAs. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) measurements reveal that our prepared MEA has very thin anode and cathode catalyst layers that come in close contact with the membrane, resulting in a MEA with low resistance and reduced mass transport limitations.     

Widening of harvesting layer and area of P3HT/PCBM bulk-heterojunction photovoltaic cells

We have fabricated P3HT/PCBM based bulk-heterojunction photovoltaic cells with P3HT layer as the hole transport layer and PCBM layer as the electron transport layer between electrode and blended P3HT/PCBM layer in order to widen the photon harvesting layer. Current density has increased by about 1 mA/cm² by the insertion of P3HT layer and the resulting conversion efficiency has been improved by about 20%. We have also fabricated a centimeter-scale active area with an efficiency of ∼1%.     

Organic solar cells with 2-Thenylmercaptan/AU self-assembly film as buffer layer

The interface between an electrode and the organic active layer is an important factor in organic solar cells (OSCs) that influences the power conversion efficiency (PCE). In this report, a buffer layer of 2-thenylmercaptan/Au self-assembly film is introduced into OSCs as a substitute for the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS) layer. The electrode/active layer interface is meliorated by Au-S coordinate bond of self assembly after applying this buffer layer. The series resistance reduces from 20 Ω cm² in a device based on PEDOT:PSS to 10.2 Ω cm². Correspondingly, the fill factor (FF) increases from 0.50 to 0.64. Moreover, due to the dipole of this self-assembled layer, the open circuit voltage (V_oc) also increases slightly from 0.54 V to 0.56 V and the PCE reaches 2.5%.     

Large-area organic photovoltaic module—Fabrication and performance

Here we describe the fabrication of the largest (233 cm² total area) organic photovoltaic (OPV) module (polymer:fullerene) to be certified by the National Renewable Energy Laboratory (NREL). OPV solar cells were fabricated at Plextronics by spin coating a blend of poly 3-hexylthiophene-2,5 diyl (P3HT) and [6,6] phenyl C₆₁ butyric acid methyl ester (PCBM) on top of our hole transport layer (HTL), Plexcore^® OC. In laboratory-scale devices (0.09 cm²), this system routinely exhibits power conversion efficiencies exceeding 3.7%. This P3HT:PCBM active layer and HTL ink system was used to scale up to the larger area module (15.2 cm×15.2 cm module size, i.e. 233 cm² total area; 108 cm² active area), which was certified by NREL as having 1.1% total area efficiency (3.4% active area efficiency).     

The effect of porosity gradient in a Nickel/Yttria Stabilized Zirconia anode for an anode-supported planar solid oxide fuel cell

In this paper, a graded Ni/YSZ cermet anode, an 8 mol.%YSZ electrolyte, and a lanthanum strontium manganite (LSM) cathode were used to fabricate a solid oxide fuel cell (SOFC) unit. An anode-supported cell was prepared using a tape casting technique followed by hot pressing lamination and a single step co-firing process, allowing for the creation of a thin layer of dense electrolyte on a porous anode support. To reduce activation and concentration overpotential in the unit cell, a porosity gradient was developed in the anode using different percentages of pore former to a number of different tape-slurries, followed by tape casting and lamination of the tapes. The unit cell demonstrated that a concentration distribution of porosity in the anode increases the power in the unit cell from 76 mW cm⁻² to 101 mW cm⁻² at 600 °C in humidified hydrogen. Although the results have not been optimized for good performance, the effect of the porosity gradient is quite apparent and has potential in developing superior anode systems.     

Optimization of the performance of polymer electrolyte fuel cell membrane-electrode assemblies: Roles of curing parameters on the catalyst and ionomer structures and morphology

In order to understand the origin of performance variations in polymer electrolyte membrane fuel cells (PEMFCs), a series of membrane-electrode assemblies (MEAs) with identical electrode layer compositions were prepared using different electrode curing conditions, their performances were evaluated, and their morphologies determined by scanning electron microscopy (SEM). The polarization curves varied markedly primarily due to differences in morphologies of electrodes, which were dictated by the curing processes. The highest performing MEAs (1.46 W cm⁻² peak power density at 3.2 A cm⁻² and 80 °C) were prepared using a slow curing process at a lower temperature, whereas those MEAs prepared using a faster curing process performed poorly (0.1948 W cm⁻² peak power density at 440 mA cm⁻² and 80 °C). The slowly cured MEAs showed uniform electrode catalyst and ionomer distributions, as revealed in SEM images and elemental maps. The relatively faster cured materials exhibited uneven distribution of ionomer with significant catalyst clustering. Collectively, these results indicate that to achieve optimal performance, factors that affect the dynamics of the curing process, such as rate of solvent evaporation, must be carefully controlled to avoid solvent trapping, minimize catalyst coagulation, and promote even distribution of ionomer.     

Polymer photovoltaic devices using highly conductive poly(3,4-ethylenedioxythiophene-methanol) electrode

In this work, modified poly(3,4-ethylenedioxythiophene) (PEDOT) was used as an anode in polymer photovoltaic devices (PVDs) based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C₆₀-butyric acid methyl ester (PCBM). We synthesized poly(3,4-ethylenedioxythiophene methanol) (PEDTM) with a transmittance of 87% (at 510 nm) and a conductivity of 700 S/cm. PEDTM was applied in photovoltaic devices as a hole transporting layer on indium-tin oxide (ITO) electrode as well as a direct anode layer. PVDs with PEDTM as hole transporting layers on ITO showed a very high short-circuit density of 14.87 mA/cm² and power conversion efficiency of 2.67% under an illumination of AM 1.5 G (100 mW/cm²). In addition, we also fabricated ITO-free PVDs using PEDTM as an anode, which exhibited a performance of 0.61% with a result of J_sc of 4.48 mA/cm², V_oc of 0.51 V, and FF of 27%.     

Ionic conducting behavior of solvent-free polymer electrolytes prepared from oxetane derivative with nitrile group

Polymer with trimethylene oxide (TMO) units prepared from ring-opening polymerization of an oxetane derivative is a candidate for the matrix of solid polymer electrolytes. We prepare an oxetane derivative with nitrile group, 3-(2-cyanoethoxymethyl)-3-ethyloxetane, CYAMEO. CYAMEO is polymerized by using a cationic initiator system. The structure of the resulted polymer, P(CYAMEO), is confirmed by NMR and FTIR spectroscopic techniques. Inorganic salts, such as lithium salts, can be dissolved in P(CYAMEO) matrix. FTIR and DSC results of P(CYAMEO)-based electrolyte films suggest that lithium ions in the P(CYAMEO) matrix interact with the nitrile side chains, mainly, and not with the oxygen atoms on the main chain of the P(CYAMEO). The conductivity at 30 °C for P(CYAMEO)-based electrolyte films, P(CYAME)10(LiX)1, is 19.6 μS cm⁻¹ (X = LiClO₄), 6.59 μS cm⁻¹ (BF₄), 6.54 μS cm⁻¹ (CF₃SO₃), and 25.0 μS cm⁻¹ (N(CF₃SO₂)₂). The rise in temperature from 30 °C to 70 °C increases their conductivity, about 30-40 times. The conductivity at 70 °C for P(CYAMEO)-based electrolyte films is 0.742 mS cm⁻¹ (X = LiClO₄) and 0.703 mS cm⁻¹ (N(CF₃SO₂)₂). Electrochemical deposition and dissolution of lithium on a nickel plate electrode are observed in the solvent-free three-electrode electrochemical cell with P(CYAMEO)10(LiX)1, (X = ClO₄ or N(CF₃SO₂)₂) electrolyte film at 55 °C.     

Efficient hybrid carboxylated polythiophene/nanocrystalline TiO2 heterojunction solar cells

Efficient hybrid solar cells fabricated from TiO₂, novel carboxylated polythiophene poly (3-thiophenemalonic acid) P3TMA as sensitizer as well as hole conductor and poly (3-hexylthiophene) (P3HT) as hole transporter was described. UV-Vis absorption and morphology of the active layer were investigated. Device J/V characterizations with different P3HT layer thickness were measured and discussed. Efficiency improvements were observed in thinner P3HT layer thickness and with poly[3,4-(ethylenedioxy)-thiophene]:poly(styrene sulfonate) (PEDOT:PSS) as charge collection layer, and such device showed a short-circuit current density of 1.32 mA/cm², an open-circuit voltage of 0.44 V, a fill factor of 0.43, and a energy conversion efficiency of 0.25% at A.M. 1.5 solar illumination (100 mW/cm²).     

Towards a compact SU-8 micro-direct methanol fuel cell

This paper presents an all-polymer micro-direct methanol fuel cell (microDMFC) fabricated with SU-8 photoresist. The present development exploits the capability of SU-8 components to bond to each other by a hot-pressing process and obtain a compact device. The device is formed by a membrane electrode assembly (MEA) sandwiched between two current collectors. The MEA consists of a porous SU-8 membrane filled with a proton exchange polymer and covered by a thin layer of carbon-based electrodes with a low catalyst loading (1.0 mg cm⁻²). The current collectors consist of two metalized SU-8 plates provided with a grid of through-holes that allow delivering the reactants to the MEA by diffusion. Fuel cell characterization was performed by measuring the polarization curves under different methanol concentrations and temperatures. The components were first tested using an external casing. A maximum power density of 4.15 mW cm⁻² was measured with this assembly working with a 4 M methanol concentration and at a temperature of 40 °C. The components were then bonded to obtain a compact micro-direct methanol fuel cell that yielded a power density of 0.65 mW cm⁻² under the same conditions. Despite this decrease in power density after bonding, the drastic reduction of the device dimensions resulted in an increase of more than 50 times the previous volumetric power density. The results obtained validate this novel approach to an all-polymer micro-fuel cell.     

Preparation and electrochemical characterization of electrospun,microporous membrane-based composite polymer electrolytes for lithium batteries

Poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} membranes incorporating 0, 6 and 10 wt.% of nano-meter sized particles of SiO₂ were prepared by electrospinning. These membranes served as host matrix for the preparation of polymer electrolytes (PEs) by activating with the non-volatile and safe room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMITFSI). The membranes consisted of layers of fibers with average fiber diameter of 2–5 μm and had a porosity of ∼87%. PEs with SiO₂ exhibited higher ionic conductivity with a maximum of 4.3 × 10⁻³ S cm⁻¹ at 25 °C obtained with 6% SiO₂. The optimum PE based on the membrane with 6% SiO₂ exhibited better compatibility with lithium metal electrode on storage and resulted in enhanced charge–discharge performance in Li/LiFePO₄ cells at room temperature, delivering the theoretical specific capacity of 170 mAh g⁻¹ at 0.1 C-rate. The PEs exhibited a very stable cycle property as well, demonstrating their suitability for lithium battery applications.     

Thin film solid oxide fuel cells with copper cermet anodes

Thin film solid oxide fuel cells (SOFCs), composed of thin coatings of 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) and thick substrates of (La_0.8Sr_0.2)_0.98MnO₃ (LSM)-YSZ cathodes, are fabricated using the conventional tape casting and tape lamination techniques. Densification of YSZ electrolyte thin films is achieved at 1275 °C by adjusting the cathode tape formulation and sintering characteristics. Two types of copper cermets, CuO-YSZ-ceria and CuO-SDC (Ce_0.85Sm_0.15O_1.925)-ceria, are compared in terms of the anodic performance in hydrogen and propane. Maximum power densities for hydrogen and propane at 800 °C are 0.26 W cm⁻² and 0.17 W cm⁻² for CuO-YSZ-ceria anodes and 0.35 W cm⁻² and 0.22 W cm⁻² for CuO-SDC-ceria anodes, respectively. Electrochemical impedance analysis suggests that CuO-SDC-ceria exhibits a much lower anodic polarization resistance than CuO-YSZ-ceria, which could be explained by the intrinsic mixed oxygen ionic and electronic conductivities for SDC in the reducing atmosphere.     

Electrical and thermal conductivities of novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells

This study prepares novel metal mesh hybrid polymer composite bipolar plates for proton exchange membrane fuel cells (PEMFCs) via inserting a copper or aluminum mesh in polymer composites. The composition of polymer composites consists of 70 wt% graphite powder and 0-2 wt% modified multi-walled carbon nanotubes (m-MWCNTs). Results indicate that the in-plane electrical conductivity of m-MWCNTs/polymer composite bipolar plates increased from 156 S cm⁻¹ (0 wt% MWCNT) to 643 S cm⁻¹ (with 1 wt% MWCNT) (D.O.E. target >100 S cm⁻¹). The bulk thermal conductivities of the copper and aluminum mesh hybrid polymer composite bipolar plates (abbreviated to Cu-HPBP and Al-HPBP) increase from 27.2 W m⁻¹ K⁻¹ to 30.0 W m⁻¹ K⁻¹ and 30.4 W m⁻¹ K⁻¹, respectively. The through-plane conductivities decrease from 37.8 S cm⁻¹ to 36.7 S cm⁻¹ for Cu-HPBP and 22.9 S cm⁻¹ for Al-HPBP. Furthermore, the current and power densities of a single fuel cell using copper or aluminum mesh hybrid polymer composite bipolar plates are more stable than that of using neat polymer composite bipolar plates, especially in the ohmic overpotential region of the polarization curves of single fuel cell tests. The overall performance confirms that the metal mesh hybrid polymer composite bipolar plates prepared in this study are promising for PEMFC application.