Micro gratings written in ZnO:Al thin films using picosecond UV‐laser interference patterning

Abstract

Diffraction micro gratings have been written in ZnO:Al thin films using a picosecond laser operating at 355 nm. Micro gratings of 20 µm diameter with a period of 860 nm show a groove depth up to 120 nm. The total transmittance of square‐centimeter‐size grating‐textured ZnO:Al films was almost unchanged after grating formation, while the sheet resistance increased moderately. The textured films reached haze values of 9% at 700 nm. This simple texturing method can be applied also to ZnO:Al films that cannot be texture etched. Illustration of the interfering laser beams and the resulting micro grating (left) and reflection from a micro grating array written in ZnO:Al on glass (right). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Light trapping for a-Si:H/µc-Si:H tandem solar cells using direct pulsed laser interference texturing

“…At higher pulse energies, too much energy is deposited; the surface melts and no grooves are formed. In previous work [25] we showed that for the laser parameters used here, no loss of transmittance of the ZnO:Al film due to laser texturing can be observed. The optical scatter properties of the front contact samples have been characterized using haze and ARS measurements.…”

“…The formation of the gratings by interfering pulsed laser beams has been discussed in the Refs. [24,25]. The grooves are deepest near the center of the micro grating where the local intensity of the interference modulated Gaussian intensity profile is strongest.…”

“…Laser interference texturing of the ZnO:Al films was performed by writing arrays of 1D micro gratings, as described previously [25]. Briefly, the picosecond UV laser (repetition rate 50 kHz, wavelength 355 nm, pulse width 10 ps, Gaussian intensity profile) of a Rofin laser scribe system equipped with a two-beam interference setup has been used.…”

“…However, no application to Si thin film solar cells has been reported. In a previous publication we explored the use of DLIP for writing grating textures with submicron periodicity into ZnO:Al layers, and showed optoelectronic properties of the textured layers relevant to applications for thin film photovoltaics. In this Letter, we use DLIP to enhance photon collection in a‐Si:H/μc‐Si:H tandem solar cells.…”

Very thin, highly‐conductive ZnO:Al front electrode on textured glass as substrate for thin‐film silicon solar cells

“…There are also other groups working with textured glasses, but in combination with, e.g., boron‐doped ZnO grown by low‐pressure chemical vapor deposition 5 or conventionally thick, wet‐chemically texturized ZnO:Al 6. We want to note that there are also other concepts for introducing light trapping such as direct laser interference patterning (DLIP) 7. In contrast to recent reports where UV nano‐imprint lithography (UV‐NIL) is used to texturize a lacquer (containing organic components) on glass 8, 9, the use of textured glass (and the DLIP approach) is also compatible with high‐temperature processes.…”