20 February 2017 Ultrafast laser scribing of transparent conductive oxides in Cu(In,Ga)Se2 solar cells via laser lift-off process: the control of laser-induced damage
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Abstract
For higher cell-to-module efficiency in Cu(In,Ga)Se2 (CIGS) thin-film solar cells, it is important to reduce the loss of active area due to integrated connection. The integrated connection contains three scribing processes: P1 (back contact insulation), P2 (electrical connection) and P3 (transparent conductive oxide, shortly TCO front contact insulation). In this work, we focused on ultrashort-pulse laser scribing (λ=1034 nm, Δτ=300 fs) of TCO via lift-off process as damage-less P3 scribing of CIGS thin-film solar cells. The lift-off of TCO was caused by laser ablation of only an upper part of CIGS light-absorbing layer. The dependence of lift-off behavior on the laser pulse energy and TCO film thickness has been investigated. It was observed that the lift-off of TCO formed a heat-affected zone (HAZ) with a thickness up to 250 nm beneath the trench bottom, where the CIGS experienced to melt. Further, thinner TCO film required lower laser energy threshold for the TCO lift-off, which is favorable to higher solar cell efficiency due to smaller HAZ. Using the TCO liftoff as P3, a submodule with an active area of approximately 3.5 cm2 made by all laser scribing exhibited the conversion efficiency of 11.6 %. After post-annealing at 85 °C for 15 h in vacuum for recovering laser-induced damages, the efficiency was successfully improved to 15.0 %, which is comparable to mechanically-scribed one.
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Aiko Narazaki, Tadatake Sato, Hiroyuki Niino, Hideyuki Takada, Kenji Torizuka, Jiro Nishinaga, Yukiko Kamikawa-Shimizu, Shogo Ishizuka, Hajime Shibata, Shigeru Niki, "Ultrafast laser scribing of transparent conductive oxides in Cu(In,Ga)Se2 solar cells via laser lift-off process: the control of laser-induced damage", Proc. SPIE 10091, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXII, 100911E (20 February 2017); doi: 10.1117/12.2266895; https://doi.org/10.1117/12.2266895
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