M A T S Photolithographic Patterning of Organic Electronic Materials

Hydrofluoroethers are shown to be benign solvents to a wide variety of organic electronic materials, even at extreme conditions such as boiling temperature. Coupled with fluorous functional photoresist-acidsensitive semi-perfluoroalkyl resorcinarene, they open new frontiers for photolithographical patterning for organic electronic systems. Summary of Research: Organic electronics is emerging as a promising technology to enable mechanically flexible devices through solution processing of organic materials [1]. As with traditional electronics, organic devices require active functional materials to be tailored into micropatterned and multi-layered device components. While the former relies on photolithographic patterning techniques, the latter is restricted from adopting such robust, high-resolution and high-throughput techniques because of the chemical compatibility issue between organic materials and patterning agents [3]. Namely, deterioration of materials’ performance occurs during the photoresist deposition and removal stages due to aggressive organic solvents, as well as in the pattern development steps by aqueous base solutions. In our search for universal, materials-friendly solvents, we have identified environmentally benign fluorous solvents combined with specifically tailored patterning materials as a possible solution to this complex problem. Fluorous solvents are poor solvents for non-fluorinated organic materials [2]. Among the variety of fluorous solvents, segregated hydrofluoroethers (HFEs) attracted our attention because of their nonflammability, zero ozone-depletion potential and low toxicity for humans [3]. We tested the impact of HFEs solvents on wellcharacterized and commercially available organic electronic materials. We demonstrated that HFE solvents do not damage or alter electronic and optoelectronic properties of wide class of organic electrnic materials, including: organic semiconductors (pentacene and poly-3-hexylthiophene (P3HT)), conducting polymer Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and organic light emitting polymers and small molecule compounds (polyfluorenes, and [Ru(bpy)3] (PF6 –)2 complex). To further demonstrate the orthogonality of HFEs to active organic material as well as to organic/metal interface we used aforementioned organic materials to make organic light emitting diodes (OLEDs) and thin film transistors (TFTs) which we characterized before and after exposing to HFE [4]. We found HFE did not significantly change the characteristic of tested devices even at elevated temperatures. For example, Figure 1 shows [Ru(bpy)3] (PF66 –)2 based electroluminescent device [5] in boiling HFE 7100 (61°C). We operated the device in the boiling HFE for one hour and did not observe any substantial change in its performance. This new dimension in solvent orthogonality which is enabled by the use of HFEs offers unique opportunities for the chemical processing of organic electronic materials. One example is in the area of photolithographic processing: One can use a photoresist that is properly fluorinated to be processable in HFEs [6]. We have successfully demonstrated this approach