Laser-microstructuring of FTO thin films for photovoltaics: influence of pulse duration

HERMAN HEFFNER; MARCOS SOLDERA; ANDRÉS FABIÁN LASAGNI

Frankfurt am Main

Congreso; FEMS EUROMAT 2023; 2023

Deutsche Gesellschaft für Materialkunde (DGM)

Transparent Conductive Oxides (TCOs) are used in solar cells for extracting photogenerated carriers and for allowing sunlight to reach the photoactive material. Therefore, controlling the electrical and optical properties of these films is crucial for the device performance. One strategy to tune the optoelectronic properties of TCOs is to modify the surface morphology by micropatterning. Particularly, Direct Laser Interference Patterning (DLIP) is a convenient method to produce periodic microtextures on the surface of TCOs by overlapping laser pulses at a controlled incidence angle. In this study, the topography and optical and electrical properties of Fluorine-doped Tin Oxide (FTO) are modified by DLIP applying ultrashort laser pulses. To investigate the influence of the pulse duration on the surface quality and the resulting properties, pulse durations ranging from 280 fs to 10 ps were applied. The surface topography was characterized by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), whereas the optical properties were measured by photospectroscopy methods and the electrical resistance was measured with the four-point probe technique. In general, well defined line-like structures were observed for all pulse durations with structure heights depending mostly on the used laser fluence. An example of the produced microtexture is shown in the SEM image of Figure 1a, which was fabricated with a pulse duration of 280 fs at a fluence of 0.84 J/cm2.A strong dependence of the pulse duration on the threshold fluence was observed. Namely a threshold fluence ranging from 0.80 mJ/cm2 for a pulse duration of 280 fs to 1.5 J/cm2 for a pulse duration of 1 ps was measured for a wavelength of 515 nm, whereas the threshold fluence increased from 0.41 to 1.10 J/cm2 as the pulse duration increased from 0.9 ps to 10 ps at a laser wavelength of 1030 nm. The optoelectronic properties were strongly modified. For instance, Figure 1b shows the diffuse transmittance at a wavelength of 700 nm as a function of the used fluence for different pulse durations. The results of this work thus show fundamental insights into the patterning of FTO thin films using ultrashort laser pulses and DLIP is demonstrated as a suitable method for the functionalization of this material for applications in optoelectronic devices.