Damage free laser ablation of SiO2 for local contact opening on silicon solar cells using an a-Si:H buffer layer
Mangersnes, K.
,
Foss, S.E.
,
Thøgersen, A.
Journal of applied physics, Vol 107 (2010), 043518
- Publ. year
- 2010
- Publ. type
- article
- Abstract
- We have used a Q-switched Nd:YVO4, diode pumped 532 nm laser with nanosecond pulses, and a spot diameter of 40 μm to ablate a layer of plasma enhanced chemical vapor deposited (PECVD) SiO2 on n-type Cz silicon, with the aim of making local contact openings on back-junction silicon solar cells. Laser pulses within the ns range are usually believed to be incompatible with processing of high efficiency solar cells because such long pulses induce too much damage into the underlying silicon lattice. This is due to thermal dissipation. In this work, a PECVD layer of a-Si:H between the n-type silicon and the dielectric layer is shown to absorb much of the laser radiation and allows for ablation at laser fluences lower than the ablation threshold of crystalline silicon. In addition, the a-Si:H layer serves as an excellent surface passivation layer for the silicon substrate. We show that it is possible to ablate PECVD SiO2 in a damage free way with fluences five times lower than those needed to ablate crystalline Si. Our results are verified experimentally with high resolution transmission electron microscopy of the crystal structure in the laser irradiated areas, and quasi-steady-state photoconductance measurements of emitter saturation currents. In addition, we have simulated the energy transfer from a ns 532 nm Gaussian shaped laser beam to a SiO2 covered Si lattice with and without the a-Si:H buffer layer. A model that coincides very well with the experiments is found.
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