Selective ablation with UV lasers of a-Si:H thin film solar cells in direct scribing configuration

Abstract

Monolithical series connection of silicon thin-film solar cells modules performed by laser scribing plays a very important role in the entire production of these devices. In the current laser process interconnection the two last steps are developed for a configuration of modules where the glass is essential as transparent substrate. In addition, the change of wavelength in the employed laser sources is sometimes enforced due to the nature of the different materials of the multilayer structure which make up the device. The aim of this work is to characterize the laser patterning involved in the monolithic interconnection process in a different configurations of processing than the usually performed with visible laser sources. To carry out this study, we use nanosecond and picosecond laser sources working at 355 nm of wavelength in order to achieve the selective ablation of the material from the film side. To assess this selective removal of material has been used EDX (energy dispersive using X-ray) analysis, electrical measurements and confocal profiles. In order to evaluate the damage in the silicon layer, Raman spectroscopy has been used for the last laser process step. Raman spectra gives information about the heat affected zone in the amorphous silicon structure through the crystalline fraction calculation. The use of ultrafast sources, such as picoseconds lasers, coupled with UV wavelength gives the possibility to consider materials and substrates different than currently used, making the process more efficient and easy to implement in production lines. This approach with UV laser sources working from the film side offers no restriction in the choice of materials which make up the devices and the possibility to opt for opaque substrates.

Selective patterning and scribing of Ti thin film on glass substrate by 532 nm picosecond laser

“…One was through the transparent glass side, called back-side scribing; the other was from the Ti film side, called front-side scribing. Some articles discussing different approaches to the patterning of thin film in solar cells application have been published [10][11][12][13][14][15][16]. The repetition frequency of the laser pulses was 100 kHz.…”

Influence of wavelength and pulse duration on the selective laser ablation of WOx, VOx and MoOx thin films

“…Picosecond pulses, due of the higher beam radius, induced a wider and more visible heat affected zone in the oxides surface. The dependence of the crater morphology on the laser wavelength and pulse duration has been observed in metals, semiconductors and polymers [16] [26] [27] [30]. Figure 1 To illustrate the effect of the ns pulses, Figure 2 shows confocal microscopy images of 532 nm ns pulses in the MoO x sample at different pulse energy.…”

Improvement of Performance of Amorphous Silicon-Germanium Thin-Film Solar Modules With Large Width P2 Process Technology

“…This process completely defines the solar cells and ensures the series connection of the cells. Some groups also use UV light (355 nm) by direct scribing [3], [4]. The required width of P1-P3 with the margins in between is depicted by the dead area width.…”