Laser enhanced gettering of silicon substrates

doi:10.1007/s11708-016-0441-7

Front. Energy

2017, Vol. 11

Issue (1) : 23-31 https://doi.org/10.1007/s11708-016-0441-7

RESEARCH ARTICLE

Laser enhanced gettering of silicon substrates

Daniel CHEN(

),Matthew EDWARDS,Stuart WENHAM,Malcolm ABBOTT,Brett HALLAM

School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Kensington NSW 2052, Australia

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Abstract

One challenge to the use of lightly-doped, high efficiency emitters on multicrystalline silicon wafers is the poor gettering efficiency of the diffusion processes used to fabricate them. With the photovoltaic industry highly reliant on heavily doped phosphorus diffusions as a source of gettering, the transition to selective emitter structures would require new alternative methods of impurity extraction. In this paper, a novel laser based method for gettering is investigated for its impact on commercially available silicon wafers used in the manufacturing of solar cells. Direct comparisons between laser enhanced gettering (LasEG) and lightly-doped emitter diffusion gettering demonstrate a 45% absolute improvement in bulk minority carrier lifetime when using the laser process. Although grain boundaries can be effective gettering sites in multicrystalline wafers, laser processing can substantially improve the performance of both grain boundary sites and intra-grain regions. This improvement is correlated with a factor of 6 further decrease in interstitial iron concentrations. The removal of such impurities from multicrystalline wafers using the laser process can result in intra-grain enhancements in implied open-circuit voltage of up to 40 mV. In instances where specific dopant profiles are required for a diffusion on one surface of a solar cell, and the diffusion process does not enable effective gettering, LasEG may enable improved gettering during the diffusion process.

Keywords gettering multicystaline silicon impurities laser doping

Corresponding Author(s): Daniel CHEN

Just Accepted Date: 19 October 2016 Online First Date: 09 November 2016 Issue Date: 16 November 2016

Cite this article:

Daniel CHEN,Matthew EDWARDS,Stuart WENHAM, et al. Laser enhanced gettering of silicon substrates[J]. Front. Energy, 2017, 11(1): 23-31.

URL:

https://academic.hep.com.cn/fie/EN/10.1007/s11708-016-0441-7
https://academic.hep.com.cn/fie/EN/Y2017/V11/I1/23

Fig.1 Process flow diagram for experiment investigating effectiveness of laser enhanced gettering

Fig.2 ECV measurement of active phosphorus dopant concentrations as a function of depth from the surface (Measurements were taken on samples with a (□) laser doped surface, (○) lightly-doped emitter and (△) screen print emitter)

Fig.3 Interstitial iron concentration [Fe_i] extracted at an injection level of Δn=9.1×10¹⁴cm⁻³ measured on samples processed under various conditions with or without an additional laser process

Fig.4 Life time and implied open-circuit voltage calibrated photo luminescence imaging (left column) and interstitial iron concentration map (right column) of adjacent multicrystalline wafers without LasEG processing (Wafer A) and with LasEG processing (Wafer B) (Measurements were made taken at 1-Sun exposure for 0.5 s using a BT Imaging LIS-R PL tool and processed using PLPro and ICARUS)

Fig.5 Extracted τ bulk of monocrystalline and multicrystalline wafers with various thermal processes and with or without laser enhanced gettering treatment

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