Effect of Nanosecond Laser Beam Shaping on Cu(In,Ga)Se₂ Thin Film Solar Cell Scribing

Abstract

The Cu­(In,Ga)­Se2 (CIGS) thin film solar cell is a promising material architecture considering its high photovoltaic (PV) efficiency at low material cost. Recently, the authors demonstrated all laser based mini-module fabrication on a transparent conducting oxide (TCO) based CIGS architecture, using a cost-effective nanosecond laser beam illuminated from the transparent glass substrate side. While indium tin oxide (ITO) is a promising TCO to this end, allowing ohmic contact with CIGS and low sheet resistance, it suffers from unwanted damage upon laser scribing based on its preferred thickness of ∼200 nm. Therefore, in this study, we investigate the effect of laser beam size and shape on ITO damage during P2 laser scribing. Although use of an enlarged laser spot could mitigate the damage issue, larger scribing width increased the dead zone. Thus, we have implemented the elliptical laser beam shaping technology so that a longer beam axis can suppress the ITO damage also maintaining high scribing speed while a shorter beam axis dictates narrow scribing width. Based on theoretical and numerical analyses, the ITO damage free scribing trend by enlarged laser beam, at least along one laser beam axis, is attributed to the buckling mechanism that facilitates film failure by enlarged laser beam. Transient thermo-mechanical modeling results imply that larger laser beam induced thermal stress will reach the film failure threshold earlier within laser pulse duration at lower interfacial temperature. However, further time-resolved experimental investigations are necessary to find the exact film delamination timing in conjunction with possible contribution of a microexplosion mechanism.

Laser Scribing of Photovoltaic Solar Thin Films: A Review

“…Employing a 64 µm beam spot size overcame this issue with the added benefit of increased scanning speeds. Moreover, using an elliptical shaped beam (21 µm × 84 µm) could suppress ITO damage, accompanied by narrower width, more straight grooves, and higher scanning speeds [65]. A similar induced ablation study using a ps laser confirmed the advantage of using an elliptical beam for selective film removal and high-quality scribes.…”

“…Moreover, lift-off ablation can be a great fit for scribing the CIGS absorber layer due to its high sensitivity to heat-induced damage even with ultrashort lasers; rear-side ablation with pressure through the Mo layer can be beneficial in this case [32]. Furthermore, new findings regarding this process indicate that enlarged laser beams may be used to avoid damage to the ITO because of the lower absorber-ITO interfacial temperature in P2-induced ablation [65].…”

“…For minimizing residue and recast layers, combining the lift-off process with a fs laser can be a practical approach to attaining a debris and damage-free surface in laser scribing of an a-Si solar cell [114]. Alternatively, using an elliptical beam in combination with the lift-off process has attained clean scribes with minimum residues [65].…”

“…Employing this approach for scribing CZTSe thin-film solar cells with an IR ps laser has improved removal quality, selectivity, and crater edge quality without the presence of defects [44]. Kuk et al [65] applied induced ablation for P2 scribing of CIGS on TCO film using a 532 nm ns pulsed laser to avoid damage in the back contact layer. This research thoroughly investigated the effects of laser beam size and beam shaping.…”

Enhanced Mechanical Stability of CIGS Solar Module with Glass/Polyimide/Indium Tin Oxide for Potentially Flexible Applications

“…However, such a challenge could be efficiently addressed via fine-tuning of pulse energy (0.1–0.5 W of laser power) and scribing speed (10–110 mm/s) using an elliptical shaped laser beam (Figure S7). While using the elliptical laser beam, the longer axis was aligned along the laser scan direction toward enhanced pulse overlap enabling increased scribing speed, , whereas the shorter axis maintained the narrow scribing width. Detailed mechanisms are under investigation.…”