TY - JOUR

T1 - Impact of surface topography and laser pulse duration for laser ablation of solar cell front side passivating SiNx layers

AU - Hermann, Sonja

AU - Dezhdar, Tara

AU - Harder, Nils Peter

AU - Brendel, Rolf

AU - Seibt, Michael

AU - Stroj, Sandra

N1 - Funding Information: The authors would like to thank the Fraunhofer-Centre of Silicon-Photovoltaics (CSP) for excellent TEM-images of the texture pyramid (Fig. 4) and J. Bonse for fruitful discus- sions about LIPSS. Funding was provided by the State of Lower Saxony and the German Federal Ministry for the En- vironment, Nature Conservation and Nuclear Safety (BMU) under Contract No 0327547A.

PY - 2010/12/1

Y1 - 2010/12/1

N2 - Local contact openings in SiNx layers that passivate the front side of solar cells offer an attractive alternative to the current standard "fire-through" screen printing process for front grid fabrication. Additionally, this technology can be used for enabling a selective emitter. In the present paper, we investigate laser ablation of SiNx layers on planar and textured silicon surfaces for various laser wavelengths and pulse durations in the nanosecond (ns) to femtosecond (fs) range. We characterize the dark J-V characteristics of diodes with laser contact openings in the SiNx layer passivating the emitter. Our results show that on alkaline textured surfaces the ablation by a ns laser produces less damage than by an ultrashort pulse laser. The dark currents of alkaline textured diodes treated with picosecond (ps) or fs lasers are one order of magnitude higher than those of ns laser treated diodes. High ideality factors furthermore indicate crystal damage in the ∼500 nm deep space charge region of the diodes. Scanning electron microscope and transmission electron microscope images of textured samples, confirm the presence of extensive and deep crystal damage after ps laser ablation, which are not observed in laser treated samples with planar surfaces. Correspondingly, for planar surfaces we find for both, ns and for ps laser ablated regions, emitter saturation current densities J0e,abl of ∼2 pA/ cm2. The recombination in textured samples in contrast differs vastly for ns and ps laser ablation. The ns laser results in an only slightly increased value of 3.7 pA/ cm2 while the ps laser treated sample was not evaluable due to severe crystal damage leading to effective lifetimes of <5μs.

AB - Local contact openings in SiNx layers that passivate the front side of solar cells offer an attractive alternative to the current standard "fire-through" screen printing process for front grid fabrication. Additionally, this technology can be used for enabling a selective emitter. In the present paper, we investigate laser ablation of SiNx layers on planar and textured silicon surfaces for various laser wavelengths and pulse durations in the nanosecond (ns) to femtosecond (fs) range. We characterize the dark J-V characteristics of diodes with laser contact openings in the SiNx layer passivating the emitter. Our results show that on alkaline textured surfaces the ablation by a ns laser produces less damage than by an ultrashort pulse laser. The dark currents of alkaline textured diodes treated with picosecond (ps) or fs lasers are one order of magnitude higher than those of ns laser treated diodes. High ideality factors furthermore indicate crystal damage in the ∼500 nm deep space charge region of the diodes. Scanning electron microscope and transmission electron microscope images of textured samples, confirm the presence of extensive and deep crystal damage after ps laser ablation, which are not observed in laser treated samples with planar surfaces. Correspondingly, for planar surfaces we find for both, ns and for ps laser ablated regions, emitter saturation current densities J0e,abl of ∼2 pA/ cm2. The recombination in textured samples in contrast differs vastly for ns and ps laser ablation. The ns laser results in an only slightly increased value of 3.7 pA/ cm2 while the ps laser treated sample was not evaluable due to severe crystal damage leading to effective lifetimes of <5μs.

UR - http://www.scopus.com/inward/record.url?scp=78751565479&partnerID=8YFLogxK

U2 - 10.1063/1.3493204

DO - 10.1063/1.3493204

M3 - Article

AN - SCOPUS:78751565479

VL - 108

JO - Journal of applied physics

JF - Journal of applied physics

SN - 0021-8979

IS - 11

M1 - 114514

ER -