Wilson Jose da Silva

A high efficiency solution processed polymer inverted triple-junction solar cell exhibiting a power conversion efficiency of 11.83%

High efficiency, solution-deposited polymer inverted double- and triple-junction solar cells are demonstrated. The devices are composed of three distinctive photosensitive materials in three distinct subcells, with minimal absorption spectral overlap, and with a bandgap ranging from 1.3 eV to 1.82 eV. A transparent hybrid inorganic organic mixture was introduced as an interconnecting layer to optically and physically connect the subcells. Accordingly, a power conversion efficiency of 10.39% was attained for the double-junction cell and a record high of 11.83% was obtained for the triple-junction cell.

Au-doped single layer graphene nanoribbons for a record-high efficiency ITO-free tandem polymer solar cell

Polymer solar cells (PSCs) are apparently becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequent use of a transparent conductive electrode, indium-tin-oxide (ITO), in the present PSC technologies has increased the overall expenses. In addition, its brittleness in nature could limit the future development of PSCs, particularly in a flexible format. Here, we report on the development of Au-doped single layer graphene nanoribbons (Au-doped SLGNRs) as an option to the transparent conducting electrode (indium tin oxide, ITO) that could yield a single-layer PSC with power conversion and external quantum efficiencies comparable to commonly used transparent electrodes. When the Au-doped SLGNRs are implemented in tandem architecture, a power conversion efficiency (PCE) of 8.48% is achieved. This is the highest efficiency for ITO-free tandem PSCs to date. The improved performance of the Au-doped SLGNR anode is characterized to the structure of the device that enables a hole transport from the active layer into the Au-doped SLGNR anode.

Very high magnetocurrent in tris-(8-hydroxyquinoline) aluminum-based bipolar charge injection devices

Bipolar devices constructed using 60nm thick tris-(8-hydroxyquinoline) aluminum (Alq3) thin films sandwiched between a 200nm thick sulfonated polyaniline hole-injection electrode and Al∕Ca electron-injection electrode show very high (up to 103%) magnetocurrent values. True-hole-only and true-electron-only Alq3-based devices that make use of Si as charge carrier collecting electrode, and Al∕Ca as electron injecting electrode or Au as hole injecting electrode, are also proposed, prepared, and characterized. In these true-single-carrier devices magnetocurrent is not observed. This result provides strong evidence that bipolar injection is a necessary condition for very high magnetocurrent observation in Alq3.

Hybrid metal-base transistor with base of sulfonated polyaniline and fullerene emitter

We demonstrate hybrid vertical architecture transistors that operate like metal-base transistors, using n-type silicon as the collector, sulfonated polyaniline as the base, and C60 fullerene as the emitter. Electrical measurements suggest that the sulfonated polyaniline base effectively screens the emitter from electric field variations occurring in the collector leading to the metal-base transistor behavior. These devices operate at low voltages and show common-emitter current gain equal to 8, which is independent of the base current up to values of ∼1.5μA and constant at collector voltages between 1 and 5V.

GO:PEDOT:PSS for High-Performance Green Phosphorescent Organic Light-Emitting Diode

A high-performance green phosphorescent organic light-emitting diode (GPhOLED) based on easily available graphene oxide (GO)-doped poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as anode buffer layer and simple device fabricating process has been demonstrated. The GO:PEDOT:PSS-based GPhOLEDs show a better performance compared to the PEDOT:PSS only GPhOLEDs with current and power efficiencies of 52 and 41 cd/A and 36 and 27 lm/W at 1000 cd/m2, respectively. These findings shed new light on the development of high-performance GPhOLEDs.

Organic devices based on nickel nanowires transparent electrode

Herein, we demonstrate a facile approach to synthesize long nickel nanowires and discuss its suitability to replace our commonly used transparent electrode, indium-tin-oxide (ITO), by a hydrazine hydrate reduction method where nickel ions are reduced to nickel atoms in an alkaline solution. The highly purified nickel nanowires show high transparency within the visible region, although the sheet resistance is slightly larger compared to that of our frequently used transparent electrode, ITO. A comparison study on organic light emitting diodes and organic solar cells, using commercially available ITO, silver nanowires, and nickel nanowires, are also discussed.

Graphene oxide grafted polyethylenimine electron transport materials for highly efficient organic devices

We demonstrate that solution processed graphene oxide (GO) grafted polyethylenimine ethoxylate (PEIE) is an efficient electron transport layer for organic solar cells with an active layer that consists of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The optimized GO:PEIE demonstrated the best efficiency of 8.21% compared to that of the GO and PEIE devices.

High performance polymer tandem solar cell

A power conversion efficiency of 9.02% is obtained for a fully solution-processed polymer tandem solar cell, based on the diketopyrrolopyrrole unit polymer as a low bandgap photoactive material in the rear subcell, in conjunction with a new robust interconnecting layer. This interconnecting layer is optically transparent, electrically conductive, and physically strong, thus, the charges can be collected and recombined in the interconnecting layer under illumination, while the charge is generated and extracted under dark conditions. This indicates that careful interface engineering of the charge-carrier transport layer is a useful approach to further improve the performance of polymer tandem solar cells.

Micropipette-Based Microfluidic Device for Monodisperse Microbubbles Generation

Microbubbles have various applications including their use as carrier agents for localized delivery of genes and drugs and in medical diagnostic imagery. Various techniques are used for the production of monodisperse microbubbles including the Gyratory, the coaxial electro-hydrodynamic atomization (CEHDA), the sonication methods, and the use of microfluidic devices. Some of these techniques require safety procedures during the application of intense electric fields (e.g., CEHDA) or soft lithography equipment for the production of microfluidic devices. This study presents a hybrid manufacturing process using micropipettes and 3D printing for the construction of a T-Junction microfluidic device resulting in simple and low cost generation of monodisperse microbubbles. In this work, microbubbles with an average size of 16.6 to 57.7 μm and a polydispersity index (PDI) between 0.47% and 1.06% were generated. When the device is used at higher bubble production rate, the average diameter was 42.8 μm with increased PDI of 3.13%. In addition, a second-order polynomial characteristic curve useful to estimate micropipette internal diameter necessary to generate a desired microbubble size is presented and a linear relationship between the ratio of gaseous and liquid phases flows and the ratio of microbubble and micropipette diameters (i.e., Qg/Ql and Db/Dp) was found.