Effects of sub-picosecond direct laser interference patterning on the optoelectronic properties of fluorine-doped tin oxide thin films

Micropatterning of metal oxides is of high interest for structuring electrodes in optoelectronic devices. In this work, the impact of infrared (IR) sub-picosecond Direct Laser Interference Patterning (DLIP) on the surface morphology, surface chemistry, optical and electrical properties of Fluorine-doped Tin Oxide (FTO) is studied. The topography characterization reveals periodic microchannels with an average height between 15 and 600 nm, depending on the applied laser fluence, decorated with Laser-Induced Periodic Surface Structures (LIPSS). The doping by aliovalent Sn atoms induced by non-linear IR absorption were revealed by X-ray Photoemission Spectroscopy (XPS) analysis. An increase in the average diffuse optical transmittance up to 730% was obtained in the spectral range 400-1000 nm as a consequence of the interaction of white light with the periodic micro- and nanostructures. The one-dimensionality of the microstructures caused a significant anisotropic electrical behavior, and an enhancement of the conductivity of up to 50% was obtained following the direction of the microchannels of the patterned films as compared to the unstructured material. Our results demonstrate that DLIP is a powerful technique for future application in structuring electrodes for highly efficient optoelectronic devices and sensors.