Silver Grid Research Articles

All-solution-processed organic solar cells with conventional architecture

All-solution processed organic solar cells with a conventional device structure were demonstrated. The evaporated low work function LiF/Al electrode was replaced by a printed high work function silver electrode combined with an additional electron transport layer (ETL). Two electron transport layers were tested: (I) zinc oxide (ZnO) nanoparticles and (II) poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN). Devices with printed silver nanoparticle inks on top of the ZnO electron transport layer lead to crack formation in the silver layer during the drying and sintering. The crack formation was avoided by using PFN as electron transport layer. The sputtered high work function ITO electrode was substituted by a printed composite electrode containing inkjet-printed silver grids in combination with high conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). All-solution processed solar cells demonstrated a power conversion efficiency of 1.94%.

All‐Solution‐Processed Transparent Thin Film Transistor and Its Application to Liquid Crystals Driving

All-solution-processed transparent thin film transistors (TTFTs) are demonstrated with silver grid source/drain electrodes, which are fabricated by printing and subsequent silver nanoparticles solution coating, which allows continuous processing without using high vacuum systems. The silver grid electrode shows a reasonable transmittance in visible range, moderate electrical conductance and mechanical strength. The TTFTs are employed to drive liquid crystal cells and demonstrate a successful switching operation.

ITO-free photovoltaic cell utilizing a high-resolution silver grid current collecting layer

AbstractAn ITO-free transparent hybrid electrode based on an embedded high resolution current collecting silver grid (Ag-grid) in combination with solution processed high conductive PEDOT:PSS (PH1000) has been demonstrated for applications in organic photovoltaic cells. The high resolution embedded Ag-grid lends low shadow loss and gives rise to current collecting layers with good electrical conductivity. Sheet resistance of the hybrid electrode combining the high-resolution Ag-grid and the PH1000 reaches several Ohms per square. Solution-processed large area flexible polymer bulk-heterojunction (BHJ) photovoltaic cells are prepared from the Ag-grid/PH1000 hybrid electrode with a configuration of hybrid electrode/PEDOT:PSS-4083/P3HT:PCBB-C8/LiF/Al. A self-assembling fullerene derivative (PCBB-C8) is chosen as the acceptor, which induces the P3HT to form ordered active layer and hence avoids the annealing process on flexible PET substrates. Power conversion efficiency (PCE) of the resulting devices reaches 1.36%.

Semi-transparent silver electrodes for flexible electronic devices prepared by nanoimprint lithography

The preparation of mechanically flexible and optically transparent electronic circuits plays a key role in the development of next-generation display technologies. Silver nano-gratings are of particular interest due to their excellent conductivity and adjustable transmittance. Printed on polymeric substrates they are suitable for an application in flexible opto-electronic devices. Here, we present the preparation of a smart silver precursor system combining both the ability of cheap and scalable nanoimprint patterning and simple thermal silver reduction. Homogeneous silver line and grid patterns with line widths down to 400 nm are prepared using poly(dimethylsiloxane) stamps in a thermal nanoimprint lithography process. Relatively low process temperatures allow the film formation on polymeric substrates. Semi-transparent silver electrodes with a resistance of 2.8 ohm are patterned on polyimide foils to prepare flexible electro-luminescence devices. A detailed investigation of the precursor's thermal decomposition behaviour as well as the resulting electrical and optical properties of the films is offered.

Large and Optically Transparent Multilayer for Broadband H-Shaped Slot Antenna

This letter presents a feasibility study of a large optically transparent broadband antenna for urban radio cellular networks. The proposed H-shaped slot antenna, which is well suited for antenna arrays, is made of three transparent and conductive layers printed on three glass substrates separated by two air gaps. The size of the antenna is close to 300×300×20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The transparent and conductive coatings used to fabricate the antenna are made of a silver grid layer (AgGL) deposited on one side of each 1.1-mm-thick 1737 Corning glass substrate. The theoretical optical transparency of the multilayer antenna ranges between 51.6% and 70.7% over the whole visible light spectrum. The measured electromagnetic performance of the transparent H-shaped slot antenna has been compared to that of a nontransparent (but geometrically identical) simulated antenna. The results show a similar behavior and performance in terms of bandwidth, radiation pattern, and gain. This confirms the restriction of the ohmic loss and skin depth loss from the AgGL material. These also provide the ability to implement large transparent antennas with performance identical to that of nontransparent ones, and most importantly with the advantage of a soft visual impact on urban environment.

Fast Inline Roll‐to‐Roll Printing for Indium‐Tin‐Oxide‐Free Polymer Solar Cells Using Automatic Registration

AbstractFast inline roll‐to‐roll printing and coating on polyethylene terephthalate (PET) and barrier foil was demonstrated under ambient conditions at web speeds of 10 m min−1 for the manufacture of indium‐tin‐oxide‐free (ITO‐free) polymer solar cells comprising a 6‐layer stack: silver‐grid/PEDOT:PSS/ZnO/P3HT:PCBM/PEDOT:PSS/silver‐grid. The first and second layers were printed at the same time using inline processing at a web speed of 10 m min−1 where flexographic printing of a hexagonal silver grid comprises the first layer followed by rotary‐screen printing of a PEDOT:PSS electrode as the second layer. The third and fourth layers were slot‐die coated at the same time again using inline processing at a web speed of 10 m min−1 of firstly zinc oxide as the electron transport layer followed by P3HT:PCBM as the active layer. The first three layers (silver‐grid/PEDOT:PSS/ZnO) comprise a generally applicable ITO‐free, semitransparent, electron‐selective front electrode for inverted polymer solar cells. This electrode shows a low sheet resistance (∼10 Ω/□) and good optical transmission in the visible range (∼60 %). The solar cell stack was completed by rotary‐screen printing of a hole‐collecting PEDOT:PSS layer at 2 m min−1 and a comb‐patterned silver‐grid back electrode at the same speed. The solar cells were post processed by using fast roll‐to‐roll switching to a functional state.

Optimization of transparent conductor-embedding front electrodes for efficient light management

An optically and electrically optimum designed front electrode is reported by using a transparent conductive oxide (TCO) film integration. A substantial enhancement of light absorption was achieved by reduction of silver (Ag) grid shading losses while holding a similar series resistance. This obviously improves the solar cell efficiency with a significant reduction in the use of Ag shading area by one fourth. Due to the optical and electrical excellent indium-tin-oxide (ITO), the TCO benefits to widen the light transparent surface and spontaneously works as an anti-reflection coating layer.We have demonstrated that a trade-off between the optical and the electrical aspects should be considered to transfer the optical benefit by ITO supporting transparent electrode to the practical electrical advantage of current enhancement. Transmission line method was applied to profile the variation of contact resistances and specific contact resistance for optimum design of ITO-integrated front electrodes.

Comparison of the Microwave Performance of Transparent Wire Monopole Antennas Based on Silver Films

In this paper, transparent printed lines used in microwave radiating structures are studied. Two transparent wire monopole antennas and an opaque reference counterpart are presented, compared, and discussed. The first transparent antenna was fabricated from a transparent conductive AgGL coating (silver grid layer: a silver/titanium bilayer deposited on a glass substrate and meshed by a standard photolithographic wet etching process). It exhibits optical transparency T of 59.2 ± 0.1% in the visible-light spectrum and sheet resistance R□ of 0.017 ± 0.001 Ω/□. The second transparent antenna was fabricated from a usual transparent conducting multilayer of indium tin oxide/silver/indium tin oxide, also deposited on a glass substrate. It exhibits optical transparency T of 71.3 ± 0.1% and sheet resistance R□ of 5.05 ± 0.05 Ω/□. Both transparent wire monopole antennas have been characterized for microwave performance and compared with an opaque reference counterpart made from a continuous silver/titanium bilayer deposited on the same glass substrate (T = 0%, R□ = 0.0025 ± 0.0002 Ω/□). Microwave measurements show similar performance for the transparent AgGL antenna and opaque reference counterpart. At 2.05 GHz, their maximum measured gains are both 4.4 ± 0.3 dBi. Conversely, the transparent indium tin oxide/silver/indium tin oxide antenna presents significant ohmic loss due to its sheet resistance value and consequently a low measured gain value (−2.1 ± 0.3 dBi maximum). This study demonstrates the relevance of the AgGL coating in the fabrication of transparent wire monopole antennas.

Top-illuminated organic solar cells fabricated by vacuum-free and all-solution processes

Solution-processable silver nanoparticles were adopted as the bottom cathode of top-illuminated organic solar cells based on a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester as the bulk-heterojunction layer. The developed device, with the top transparent anode based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and silver grids, shows a power conversion efficiency of 1.27% with a fill factor of 53.8% compared to 1.53% efficiency and 53.9% fill factor from the control devices fabricated by a vacuum-evaporated bottom cathode. The newly developed device demonstrated the feasibility of this alternative approach to developing an all-solution and vacuum-free route for fabricating large-area devices using wet coating processes in atmospheric pressure.

Fast printing of thin, large area, ITO free electrochromics on flexible barrier foil

Processing of large area, indium tin oxide (ITO) free electrochromic (EC) devices has been carried out using roll-to-roll (R2R) processing. By use of very fine high-conductive silver grids with a hexagonal structure, it is possible to achieve good transparency of the electrode covered substrates and when used in EC devices switching times are similar to corresponding ITO devices. This is obtained without the uneven switching of larger areas, which is generally observed when using ITO because of its high-sheet resistance. The silver electrode structures for 18 × 18 cm2 devices can be processed at high speed (10 m/min) on PET by flexographic printing and the EC polymer ECP-Magenta as well as a minimal color changing polymer MCCP by slot-die coating, showing the potential for fast fabrication of large volumes of low-priced flexible EC devices by use of R2R processing techniques. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Aerosol jet printed grid for ITO-free inverted organic solar cells

Aerosol jet printing is investigated as a new deposition method for a current collecting grid in indium tin oxide (ITO) free organic solar cells with an inverted layer sequence. In this device configuration, the ITO layer which usually serves as the hole contact is replaced by a transparent highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in combination with a silver grid deposited by aerosol jet printing. Since the cells are illuminated from the grid side, the optimisation of the grid design is a trade-off between area coverage and conductivity of the grid lines. These factors have been controlled by the printing parameters such as chuck temperature, printing speed and the number of printing passes. In this paper, we demonstrate that continuous, conductive grid lines with a minimum line width of 58μm can be processed on the top of the PEDOT:PSS layer. For single pass printing the area coverage varied from 5.8% to 11.9% with corresponding effective sheet resistances ranging from 8.9Ω to 1.5Ω. The ITO-free inverted devices with aerosol jet printed grid (an active area of 1.1cm2) show comparable performance to the cells with an evaporated gold grid. The effective sheet resistance can be further decreased by multiple printing passes without increasing the area coverage proportionally due to an improved aspect ratio. By increasing the conductivity and aspect ratio by multiple line printing, the cell length in the module structures can be significantly extended.

Fabrication of grid type dye sensitized solar modules with 7% conversion efficiency by utilizing commercially available materials

ABSTRACTA process to fabricate a parallel connection dye‐sensitized solar cell (DSSC) module has been developed using commercially available materials and screen printed silver grid. The process is not only simple but also easy to manipulate and therefore facilitates researchers in evaluating new materials in a module platform. By changing the design of the silver grid pattern, it was found that the performance of DSSC modules can be controlled. With the silver grid, DSSC modules have shown that a 7% conversion efficiency can be reached. Modules fabricated by this process, but with a non‐volatile electrolyte system, passed a 60 °C, 1000 h thermal aging test. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Silver front electrode grids for ITO-free all printed polymer solar cells with embedded and raised topographies, prepared by thermal imprint, flexographic and inkjet roll-to-roll processes

Semitransparent front electrodes for polymer solar cells, that are printable and roll-to-roll processable under ambient conditions using different approaches, are explored in this report. The excellent smoothness of indium-tin-oxide (ITO) electrodes has traditionally been believed to be difficult to achieve using printed front grids, as surface topographies accumulate when processing subsequent layers, leading to shunts between the top and bottom printed metallic electrodes. Here we demonstrate how aqueous nanoparticle based silver inks can be employed as printed front electrodes using several different roll-to-roll techniques. We thus compare hexagonal silver grids prepared using either roll-to-roll inkjet or roll-to-roll flexographic printing. Both inkjet and flexo grids present a raised topography and were found to perform differently due to only the conductivity of the obtained silver grid. The raised topographies were compared with a roll-to-roll thermally imprinted grid that was filled with silver in a roll-to-roll process, thus presenting an embedded topography. The embedded grid and the flexo grid were found to perform equally well, with the flexographic technique currently presenting the fastest processing and the lowest silver use, whereas the embedded grid presents the maximally achievable optical transparency and conductivity. Polymer solar cells were prepared in the same step, using roll-to-roll slot-die coating of zinc oxide as the electron transport layer, poly-3-hexylthiophene:phenyl-C(61)-butyric acid methyl ester (P3HT:PCBM) as the active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the top electrode, along with a flat bed screen printed silver grid. The power conversion efficiency (PCE) obtained for large area devices (6 cm(2)) was 1.84%, 0.79% and 1.72%, respectively, for thermally imprinted, inkjet and flexographic silver grids, tested outside under the real sun. Central to all three approaches was that they employed environmentally friendly solvents, i.e. water based nanoparticle silver inks.

Microscopy study of snail trail phenomenon on photovoltaic modules

Snail trails on photovoltaic modules are a source of enormous concern to the solar industry as no scientific reports on the mechanisms producing this global phenomenon were previously available. Here, for the first time, we clarify the origin of these snail trails as a product of the formation of silver carbonate nanoparticles which discolor the silver grid. Micropore arrays on the silicon substrate within the snail trail region could accelerate the discoloration by offering reactive compounds via penetration and release. The potential mechanisms of photovoltaic module discoloration are proposed, yielding clues as to how snail trail formation can be mitigated by technical solutions. Aging tests on the discolored modules suggest no significant power degradation or discolored area enlargement after accelerated aging.

Current Collecting Grids for ITO‐Free Solar Cells

AbstractIndium‐tin‐oxide (ITO) free polymer solar cells prepared by ink jet printing a composite front electrode comprising silver grid lines and a semitransparent PEDOT:PSS conductor are demonstrated. The effect of grid line density is explored for a large series of devices and a careful modeling study enabling the identification of the most rational grid structure is presented. Both optical and light beam induced current (LBIC) mapping of the devices are used to support the power loss model and to follow the evolution of the performance over time. Current generation is found to be evenly distributed over the active area initially progressing to a larger graduation in areas with different performance. Over time coating defects also become much more apparent in the LBIC images.

Environmental and economic assessment of ITO-free electrodes for organic solar cells

The use of Indium–Tin Oxide (ITO) as a transparent conductor in organic photovoltaic (OPV) devices has been shown to present a bottleneck for the technology due to the use of the rare metal Indium and also the energy intensive manufacturing processes required and subsequent high economic cost. This study discusses some of the alternative materials, which are being considered for use as transparent conductors in OPV modules. A life cycle and cost analysis of a number of the most promising ITO-free transparent conductors, namely: high conductivity PEDOT:PSS; a silver grid embedded in PEDOT:PSS; silver nanowires; single walled carbon nanotubes are completed in this study. The results show that there is great potential for reducing both the energy pay-back time and the cost of OPV modules by replacing ITO with an alternative transparent conductor.

Simple Approach of Fabricating High Efficiency Si Nanowire/Conductive Polymer Hybrid Solar Cells

We present a simple approach of fabricating high-efficiency hybrid solar cells based on silicon nanowires (SiNWs) and a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). PEDOT:PSS is directly spin coated on vertical SiNW arrays fabricated by electroless chemical etching to form a core-sheath heterojunction. A silver grid is used as the top anode. Compared to a planar Si/PEDOT:PSS cell, the power conversion efficiency of a 1-cm2 SiNW/PEDOT:PSS cell increases greatly from 6.2% to 9%. Cells with different SiNW lengths are also studied, and it is found that enhanced aggregation of longer SiNWs leads to poor surface coverage by PEDOT and, hence, degraded solar cell characteristics.

Highly efficient Si-nanorods/organic hybrid core-sheath heterojunction solar cells

We report a hybrid solar cell based on well-aligned crystalline silicon nanorods (SiNRs) and an organic semiconductor, 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD), in a core-sheath heterojunction structure. The device is formed by spin coating Spiro-OMeTAD on SiNRs array fabricated by electroless chemical etching. A silver grid on a conductive poly (3,4-ethylene-dioxythiophene): polystyrenesulfonate layer is used as the top transparent anode. A power conversion efficiency of 10.3% has been obtained for a 1-cm2 cell with 0.35-µm long SiNRs. The high efficiency and simple solution process used suggest that such devices are promising for developing low cost and high efficiency SiNRs/organic solar cells.

ITO-free flexible polymer solar cells: From small model devices to roll-to-roll processed large modules

Manufacturing of flexible ITO-free polymer solar cell modules by roll-to-roll methods (R2R) is described. Inverted devices with top illumination were built on a Kapton foil and an Aluminum/Chromium bi-layer system was used as electron contact. The layer structure was Kapton/Al/Cr/P3HT:PCBM/PEDOT:PSS/Ag (printed) and devices were encapsulated. Small area cells (3 cm 2 active area) were first carefully optimized investigating the influence of a number of discrete parameters on performance. A maximum power conversion efficiency of 1.4% was achieved under 1 sun illumination (AM 1.5G, 1000 W m −2). Optimized lab-scale single devices were then transferred to a full R2R process combining slot-die coating and screen printing. All the layers were processed from solution under ambient conditions. Two different concepts were explored: (i) serially connected stripe modules (to reduce the Ohmic losses) and (ii) monolithic modules (to achieve high geometric fill factor and increase the flexibility of the process). For this second concept, the only layer that needs to be patterned is the silver grid electrode and the grid pattern design can then be readily tuned. As an example, four different patterns were used and the resultant performances compared. Modules comprising 16 serially connected cells gave total area efficiencies up to 0.5% (235 cm 2 – 1% on the active area) while the best monolithic ones gave 0.35% (100 cm 2 – 0.4% on the active area). The freshly prepared devices consistently showed an inflection point in the IV curve indicative of a rather poor photovoltaic behavior. Upon light exposure and repeated IV scans the inflection point partially disappeared, and performance significantly increased.

ITO-free flexible organic solar cells with printed current collecting grids

The presence of a transparent conductive electrode such as indium tin oxide (ITO) limits the reliability and cost price of organic photovoltaic devices as it is brittle and expensive. Moreover, the relative high sheet resistance of an ITO electrode on flexible substrates limits the maximum width of a single cell. We have developed an alternative ITO-free transparent anode, based on solution processed high conductive PEDOT:PSS in combination with a printed current collecting grid. The screen printed silver grid demonstrates a typical sheet resistance of 1 Ω/□ with 6.4–8% surface coverage. The efficiency of a flexible device with an active area of 4 cm 2 with such a grid is much higher than a similar device based on ITO. Furthermore, as this composite anode is solution-processed, it is a step forward towards low-cost large area processing.