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.

Indium-doped tin oxide free electrochromic devices are prepared by coating electrochromic polymers onto polyethylene terephthalate substrates encompassing two different silver grids as electrodes. One design comprises a fl exoprinted highly conductive silver grid electrode, yielding electrochromic devices with a response time of 2 s for an optical contrast of 27%. The other design utilizes an embedded silver grid electrode whereupon response times of 0.5 s for a 30% optical contrast are realized when oxidizing the device. A commercially available conductive poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate acid) formulation (PEDOT:PSS) is coated onto the silver grids as a charge balancing polymer, and is in this setting found to be superior to a polypyrrole previously employed in electrochromic devices. In addition, the PEDOT:PSS layer increases the conductivity in the hexagonal grid structure. DOI . IntroductionThe development of electrochromic devices (ECDs) has moved from laboratory conditions into pilot plants; whereby, new challenges have emerged that include avoidance of vacuum processing steps and use of simple printing, coating, and lamination methods for deposition and assembly of the devices. If these challenges are successfully addressed, polymer based electrochromic devices will be commercially attractive and competitive to existing solutions. A main obstacle is the replacement of indium-doped tin oxide (ITO) as the transparent electrode material. ITO has been widely used as electrode material in organic electronics, but due to the scarcity of indium, substituting this material for a less expensive one would signifi cantly reduce production costs of ECDs. [1][2][3] Another incitement to replace ITO is the vast amount of energy used in the sputtering process employed in the production of ITO covered substrates. By avoiding such energy consuming processes, one would be able to manufacture ECDs with limited energy consumption from materials, to manufacturing and operation.From an operational point of view, the use of ITO as electrode material in ECDs is problematic since a low concentration of charge carriers in ITO gives rise to a large sheet resistance. It has been established that the electrode resistance has a marked effect on the response time and optical contrast of an ECD, [ 4 ] and high electrode resistance leads to a non-uniform potential across the electrode (Ohmic loss), and a non-uniform current distribution in the electrolyte. [ 5 ] By using electrodes of moderate conductivity, increasing potentials are needed to achieve satisfactory response times and optical contrast, as the ionic mobility (already impeded by the semisolid gel electrolyte) partly depends on the electric fi eld between the two electrodes. Due to several other chemical components, increasing the potential confl icts with the voltage limits, outside of which side reactions are likely to occur. These could be redox reactions of water due to moisture in the device or irreversible oxidation or reduction of the polymer fi...

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The roll-printed electrodes of organic thin-film transistors (OTFTs) were fabricated by gravure or flexography printing using engraved plates with various channel lengths and nanoparticle silver (Ag) pastes on flexible 150 Â 134 mm 2 plastic substrates. The roll-printed OTFTs used poly(vinyl phenol) (PVP) polymeric dielectrics and bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) organic semiconductors. Depending on the choice of the type of roll-printing method, the printed OTFTs obtained had a field-effect mobility between 0.08 and 0.1 cm 2 V À1 s À1 , an on/off current ratio between 10 4 and 10 5 , and a subthreshold slope between 1.94 and 2.53 V/decade. The roll printing and soluble processes made it possible to fabricate a printed OTFT with a channel length between 16 to 62 mm on a plastic substrate; this was not previously possible using traditional printing techniques. The proposed fabrication process was 20 steps shorter than conventional fabrication techniques.

A rapid increase in power conversion efficiencies in colloidal quantum dot (QD) solar cells has been achieved recently with lead sulphide (PbS) QDs by adapting a heterojunction architecture, which consists of small-area devices associated with a vacuum-deposited buffer layer with metal electrodes. The preparation of QD solar modules by low-cost solution processes is required to further increase the power-to-cost ratio. Herein we demonstrate all-solution-processed flexible PbS QD solar modules with a layer-by-layer architecture comprising polyethylene terephthalate (PET) substrate/indium tin oxide (ITO)/titanium oxide (TiO2)/PbS QD/poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS)/Ag, with an active area of up to 30 cm(2), exhibiting a power conversion efficiency (PCE) of 1.3% under AM 1.5 conditions (PCE of 2.2% for a 1 cm(2) unit cell). Our approach affords trade-offs between power and the active area of the photovoltaic devices, which results in a low-cost power source, and which is scalable to larger areas.