Wojciech Haske

Bio: Wojciech Haske is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: OLED & Polymer. The author has an hindex of 9, co-authored 18 publications receiving 2205 citations.

A Universal Method to Produce Low―Work Function Electrodes for Organic Electronics

Abstract: Organic and printed electronics technologies require conductors with a work function that is sufficiently low to facilitate the transport of electrons in and out of various optoelectronic devices. We show that surface modifiers based on polymers containing simple aliphatic amine groups substantially reduce the work function of conductors including metals, transparent conductive metal oxides, conducting polymers, and graphene. The reduction arises from physisorption of the neutral polymer, which turns the modified conductors into efficient electron-selective electrodes in organic optoelectronic devices. These polymer surface modifiers are processed in air from solution, providing an appealing alternative to chemically reactive low–work function metals. Their use can pave the way to simplified manufacturing of low-cost and large-area organic electronic technologies.

65 nm feature sizes using visible wavelength 3-D multiphoton lithography.

Abstract: Nanoscale features as small as 65 +/- 5 nm have been formed reproducibly by using 520 nm femtosecond pulsed excitation of a 4,4'-bis(di-n-butylamino)biphenyl chromophore to initiate crosslinking in a triacrylate blend. Dosimetry studies of the photoinduced polymerization were performed on chromophores with sizable two-photon absorption cross-sections at 520 and 730 nm. These studies show that sub-diffraction limited line widths are obtained in both cases with the lines written at 520 nm being smaller. Three-dimensional multiphoton lithography at 520 nm has been used to fabricate polymeric woodpile photonic crystal structures that show stop bands in the near-infrared spectral region.

Crosslinking Using Rapid Thermal Processing for the Fabrication of Efficient Solution‐Processed Phosphorescent Organic Light‐Emitting Diodes

Abstract: Copolymers with a triscarbazole hole-transport group and an oxetane or benzocyclobutene crosslinkable group can be readily thermally crosslinked on timescales of 30 min or less, with rapid thermal processing (RTP) being highly effective for this purpose. Devices with RTP-crosslinked hole-transport layers and spin-coated emissive layers exhibit high external quantum efficiencies of up to 15%.

Interface engineering of highly efficient perovskite solar cells

Abstract: Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

An electron acceptor challenging fullerenes for efficient polymer solar cells.

Abstract: A novel non-fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy-level variability, is designed and synthesized. Fullerene-free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion effi ciencies of up to 6.8%, a record for fullerene-free PSCs.

Polymers for 3D Printing and Customized Additive Manufacturing

Abstract: Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Abstract: Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.