Submicrometer Spatially Controlled Doping of Polymer Thin Films by a Single-Step Soft-Contact Approach

Polymer thin films have become increasingly popular for the fabrication of large-area and flexible devices. Doping of organic thin films is a powerful strategy to achieve highly efficient devices with precise and reliable control of their key parameters and to expand their range of applications. However, the spatially controlled doping of polymer thin films is a challenging task that has yet to be adequately addressed. Herein, we report an effective strategy for local doping of polymer thin films with submicrometer lateral resolution in a single step. We use optically inert poly(methyl methacrylate) (PMMA) and blue-fluorescent poly(9,9-di-n-octylfluorenyl-2,7-diyl) (F8 or PFO) thin films as models to investigate the doping process with different photoluminescent dyes (Rhodamine 101, Fluorescein 27, Coumarin 2 and DCM) by fluorescence microscopy, laser scanning confocal microscopy and localized and photoluminescence spectroscopy. Further insights into the doping mechanism are provided by computational studies. We show that the use of soft stamps as spatially confined doping tools allows for localized doping of the polymer thin film through dye diffusion without compromising the film morphology. This strategy overcomes solvent compatibility constraints typical of organic material processing and can be additive, allowing thin films to be doped with multiple dyes with independent control over their spatial distribution. These results strongly support the effectiveness of stamp-assisted doping as a highly versatile and reliable approach for achieving the spatially controlled doping of polymer thin films, thereby opening opportunities for organic optical and optoelectronic applications.