All-solution-processed PbS quantum dot solar modules.

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.

Fabrication and characterization of flexible thin film super-capacitor with silver nano paste current collector.

Flexible thin film super-capacitors with the silver paste current collector were printed and their electrochemical characteristics were investigated to apply for a low cost solution-based printing process. The silver paste current collector was printed on a flexible Polyethylene Telephtalate (PET) substrate and the activated carbon electrode was printed in a sequence by using a mature screen printing. In experimental evaluation, three silver pastes with different solid contents were prepared and compared because sheet resistance depended on the thickness of the current collector. By using the confocal image, the thickness of the printed electrode of the activated carbon was measured to be 27.8 microm. Cyclic voltammogram, the specific capacitance and impedence together with capacitance retension were examined to determine the performance of the printed super-capacitor. The highest specific capacitance of 53.05 F/g at a scan rate of 10 mV/s was obtained. The measurement results show that the printed super-capacitors with the silver paste current collector have a great potential to apply for wearable electronics and protable electronic devices.

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.

Fabrication of transparent conductive electrode film using thermal roll-imprinted Ag metal grid and coated conductive polymer.

In this study, to fabricate a low-resistance and high optical transparent conductive electrode (TCE) film, the following steps were performed: the design and manufacture of an electroforming stamp mold, the fabrication of thermal-roll imprinted (TRI) poly-carbonate (PC) patterned films, the manufacture of high-conductivity and low-resistance Ag paste which was filled into patterned PC film using a doctor blade process and then coated with a thin film layer of conductive polymer by a spin coating process. As a result of these imprinting processes the PC films obtained a line width of 10 +/- 0.5 Mm, a channel length of 500 +/- 2 microm, and a pattern depth of 7.34 +/- 0.5 microm. After the Ag paste was used to fill part of the patterned film with conductive polymer coating, the following parameters were obtained: a sheet resistance of 9.65 Omega/sq, optical transparency values were 83.69% at a wavelength of 550 nm.

Roll-printed organic thin-film transistor using patterned poly(dimethylsiloxane) (PDMS) stamp.

The roll-printed gate, source, and drain electrodes of organic thin-film transistors (OTFTs) were fabricated by gravure printing or gravure-offset printing using patterned poly(dimethylsiloxane) (PDMS) stamp with various channel lengths and low-resistance silver (Ag) pastes on flexible 150 x 150 mm2 plastic substrates. Bottom-contact roll-printed OTFTs used polyvinylphenol (PVP) as polymeric dielectric and bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) as organic semiconductor; they were formed by spin coating or ink-jetting. Depending on the choice of roll-printing method, the printed OTFTs obtained had a field-effect mobility of between 0.08 and 0.1 cm2/Vs, an on/off current ratio of between 10(4) and 10(5), and a subthreshold slope of between 1.96 and 2.32 V/decade. The roll-printing using patterned PDMS stamp and soluble processes made it possible to fabricate a printed OTFT with a channel length of between 12 to 74 microm on a plastic substrate; this was not previously possible using traditional printing techniques. The proposed fabrication process was 20 steps shorted than conventional fabrication techniques.

Direct-printed organic thin-film transistor using PDMS stamp and low viscosity nanosilver ink.

The contact electrodes of printed organic thin-film transistors (OTFTs) were fabricated by direct printing using patterned hard poly(dimethylsiloxane) (h-PDMS) stamp with injection channel onto flexible poly(ethylenenaphthalate) (PEN) plastic substrates, wherein low-viscosity and low-resistance conductive nanoparticle silver (Ag) ink was injected. The source and drain electrodes (W/L = 500 microm/5 microm, 500 microm/10 microm, and 500 microm/20 microm) of printed OTFT were fabricated by direct printing. The printed OTFT with polyvinylphenol (PVP) as polymer dielectric layer was formed by spin coating and poly(3-hexylthiopene-2,5-dily) (P3HT) as organic semiconductor layer was ink-jet printing. The printed OTFT was characterized in air and the following parameters were obtained: a mobility of 0.06 (+/- 0.02) cm2/Vs, an on/off current ratio of 10(4) and a subthreshold slope of 2.53 V/decade. The direct printing using patterned h-PDMS stamp for ink injection patterning made it be possible to fabricate printed OTFT with a channel length as below as to 5 microm. The number of steps in the fabrication process was reduced by 20 steps compared with photolithography.