(164e) Mixed Solvents for Rapid Photo-Thermal Patterning of Conjugated Polymers

OPVs (Organic Photovoltaics) have received widespread attention due to their promising qualities like solution processability, low temperature manufacture, tunable electronic properties and cheap and lightweight materials. A significant obstacle for the industrial development of OPVs is the lack of a patterning technology that is inexpensive, rapid and viable. Patterning helps create deep light trapping structures which help improve light capture in sub-band gap states. The aim of this project is to optically write lateral light trapping structures into Bulk Heterojunction layers by upscaling optical patterning using photo-thermal lithography. The light trapping structures will increase the external quantum efficiency of the sub-gap Charge Transfer-state absorbance across a broad wavelength range. Photo-thermal lithography (Set up shown in Fig 1) uses light to locally heat a conjugated film, which causes the heated polymer to dissolve into a solvent layer (Assembly of solvent cell shown in Fig 2). The critical design parameters are to maximize the pattern resolution and write-speed, which are both governed by the solvent quality. This presentation demonstrates a reproducible method to measure the solvent processing window for photo-thermal lithography using mixed strong and weak solvents such that polymer will not dissolve at room temperature, but will dissolve completely when laser heated to a specified dissolution temperature as depicted in the process diagram(Fig 4). We then demonstrate photo-thermal patterning of P3HT wires with < 1 µm diameter as a function of solvent quality and laser dose to demonstrate the functional relationship. Using these process parameters, we can achieve rapid sub-micro patterning, demonstrating viable patterning of OPV materials.