Microlithographic process for patterning conjugated emissive polymers

Abstract

Optoelectronic devices, such as light emitting diodes (LEDs), are an emerging technology where organic materials are finding a niche."] Initial reports of polymer-based electroluminescence used poly(p-phenylenevinylene) (PPV), albeit with inefficient quantum yield. ['] In recent years, new materials and optimization of devices, in particular choice of electrode13] and multiple-layer structures,[41 have raised the level of performance to quantum yields of up to 4 %. ['I Flexible, all-plastic as well as inverted cylindrical devices ['] exist, illustrating the drive and ingenuity for new device configurations. By taking advantage of the porous cavities in microfiltration membranes, LEDs have also been produced on the micrometer and submicrometer scale for potential use as light sources in scanning near-field optical microscopes.lxl Control over spatial arrangement and dimensions of conjugated materials will play an important role in diversifying their applications. In this communication we report a microlithographic process for patterning PPV and show preliminary results from pixel-like LED arrays prepared by this new technique. Standard photolithography used in the fabrication of integrated circuits['' is merged with the synthesis of conjugated emissive polymers to create well-defined microscalar-patterned LEDs.There is abundant precedent in the literature that indicates that the method of PPV synthesis influences LED performance. The choice of synthetic route also determines, to a great extent, the material's processability and therefore limits the types of applications. The paracyclophane route to PPV["'I has a number of distinct advantages over previous synthetic methods. '"] Because the polymerization is living, the average degree of polymerization can be controlled and optimized to maximize photoluminescence quantum PPV can also be incorporated into block copolymers to modify properties such as solubility and viscosity. Another important feature of the method are the mild conditions (thermally at 105 "C or at 50-60 "C in the presence of HC1) that convert precursor material to conjugated PPV. Scheme 1 illustrates how poly(9-hydroxy-[2.2]-paracyclophan-l-ene),-block-poly(norbornene), (poly1,-block-polyNBE,; subscripts refer to the average degree of polymerization) converts to PPVZ-block-poly-NBE,The acute sensitivity towards acid catalysis in the elimination step of poly(paracyc1ophenes) opens the door to applications in microlithography. To accomplish the elimination in discrete areas, we take advantage of photoacid generators. These molecules generate acids upon photolysis and have found applications in photoresist technology, where acid catalysis is responsible for structural changes at the molecular level. If this reaction is controlled within the irradiated areas then outstanding definition is possible.["] The overall photolithographic sequence using poly(paracyclophene) is illustrated in Scheme 2 for the preparation of PPV2,-block-polyNBE,. First, a uniform film containing poly1,-block-polyNBE, and th...

Advanced syntheses and microfabrications of conjugated polymers, C60-containing polymers and carbon nanotubes for optoelectronic applications

“…Similarly, micropatterns of PPV with patterned emissions have also been prepared from several copolymers containing PPV precursors through a selectively thermolysis, with or without involving a photoinitiator [127,128]. Besides, PPV has also been microstructured in a nondoped form by UV interferometry [126], as the transformation from the unsubstituted PPV precursor polymer (i.e.…”

Semiconducting (Conjugated) Polymers as Materials for Solid-State Lasers

“…[2] Currently, polymer light-emitting diodes (LEDs), [3,4] photodetectors, [5] photovoltaic cells, [6] sensors, [7] and field-effect transistors [8±10] are all being pushed towards commercialization by academic and industrial research teams. These devices are important not only because they perform well, but because they can be patterned by inexpensive techniques such as spin casting, photolithography, [11,12] ink jet printing, [13,14] screen printing, [15] and micromolding [16] onto almost any type of substrate, including flexible ones. [17] Notably absent from the list of electronic and optical devices that can be made from conjugated polymers is one of the most important devices for modern technologyÐthe diode laser.…”

Photoprocessable copolyimides with carbazole groups

“…A problem that has, however, hardly been tackled with these materials is the lateral structure formation, which are only described in a few papers 5,6) . Lateral structure is easily achieved with different types of photoresists.…”