Optoelectronic performance of indium tin oxide thin films structured by sub-picosecond direct laser interference patterning

Abstract

A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 µm and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1900%, respectively, was obtained in the 400–1000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.

Fabrication of Smart Materials Using Laser Processing: Analysis and Prospects

“…LIPSS features align perpendicular to the laser polarization, extending on both the bottom and sidewalls of the texture. Spatial frequencies of DLIP and LIPSS are identified, with a spatial period of Λ DLIP = 5.0 ± 0.1 µm for DLIP and Λ LIPSS = 230 ± 20 nm for LIPSS [124]. cm −2 .…”

“…This makes DLIP a potent and efficient technique for modifying surface properties across a spectrum of technological applications, encompassing electrical, optical, and tribological domains. The studies [123,124] provided a comprehensive discussion of direct laser interference patterning (DLIP), a high-throughput surface structuring method using overlapping laser beams, with applications in industries like photonics, optoelectronics, nanotechnology, and biomedicine. Figure 8 showcases the DLIP treatment of ~500 nm-thick indium tin oxide (ITO) thin films on glass substrates using a DLIP workstation equipped with a solid-state ultrashort-pulse laser with a maximum output power of 100 W and a pulse frequency of 1 MHz.…”

“…LIPSS features align perpendicular to the laser polarization, extending on both the bottom and sidewalls of the texture. Spatial frequencies of DLIP and LIPSS are identified, with a spatial period of ΛDLIP = 5.0 ± 0.1 μm for DLIP and ΛLIPSS = 230 ± 20 nm for LIPSS [124]. The process of microstructuring in DLIP can engage either photothermal, photochemical, or a combination of these mechanisms, depending on the interaction between laser light and the utilized materials [125].…”

The development of direct laser interference patterning: past, present, and new challenges

“…Beam-shaped interference configurations: other configurations for DLIP that have been developed include the use of beam shaping elements, e.g., to obtain elongated laser sub-beams that are later overlapped and thus produce interference patterns. One developed configuration has been conceived for high-power laser applications and uses a prism or DOE for beam splitting, a set of cylindrical lenses to expand the laser beam in one direction and the other optics for overlapping the produced sub-beams [20]. This setup, in general, has a deep focus of a few hundred micrometers.…”