Stress and doping uniformity of laser crystallized amorphous silicon in thin film silicon solar cells

Abstract

Simultaneous and locally resolved determination of the mechanical stress variation and the free hole concentration using Raman spectroscopy is demonstrated in laser crystallized amorphous silicon layers. Such layers are often used for the fabrication of thin film solar cells, e. g., on borosilicate glass substrates. The combined effects of stress and doping on the Raman signal can be separated based on the use of three wavelengths in the visible. The results show that the free hole concentration in the samples investigated varies between 1 x 10(18) and 1.3 x 10(19) cm(-3). Stress as well as the free hole concentration vary substantially within the sample. The stress level varies between 575 and 850 MPa (+/- 12 MPa). Cross-sectional transmission electron microscopy images show the presence of extended lattice defects such as dislocations and grain boundaries in the crystallized Si layer which could account for the lateral stress variations detected by Raman spectroscopy. The impact of film inhomogeneity in terms of stress and doping on the performance of a solar cell will be discussed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3319654

Microscale Spatially Resolved Characterization of Highly Doped Regions in Laser-Fired Contacts for High-Efficiency Crystalline Si Solar Cells

“…18 cm −3 not only exhibit the so-called 303 Fano resonance, but also show a red shift in the Raman peak 304 maximum [19]. The expected theoretical peak shift induced by 305 an increase in doping satisfies: Table I) takes values of about Finally, the study of LFCs was completed by their character-362 ization by means of c-AFM measurements.…”

“…C-AFM 386 data is in great agreement with Raman and PL data showed in 387 the first part of the work, where highly doped regions of the 388 contact processed at 1.43 W were detected at the border of the 389 contact. [18], and [19]. A. Roigé is with MATGAS Research Center, 08193 Bellaterra, Spain (e-mail: aroige@matgas.org).…”

Microscale Characterization of Surface Recombination at the Vicinity of Laser-Processed Regions in c-Si Solar Cells

“…The study of the line-shape of the first order c-Si Raman peak can give us important information about specific c-Si properties like doping [20], crystallinity [21] or mechanical stress [22]. Raman results are shown in Fig.…”

“…As it can be observed, the characteristic transverse optical (TO)-phonon mode of c-Si (520.9 cm −1 ) evidences a Raman shift at the very central point of the spot (point 3), whereas points out of the laser spot (point 1 and point 5), and even points in the outer region inside the spot (point 2 and 4), do not evidence any change at all. The red shift at the central part of the laser spot, which increases for a LPRs performed at 2 W (gray spectrum with crossed points), is representative of a stressed Si structure [22], and can be induced by the laser processing. These conclusions are in agreement with an exhaustive micro-Raman spectroscopy analysis of LPRs presented elsewhere [9].…”

Future of raman in PV development

“…The stress map was corrected for the compressive contributions produced by the Fano effect using equation 9 from [5] and by the addition of boron by means of the lattice parameter using Vergard's law [14]. The nonuniform distribution of defects inside the laser crystallized seed layer is supported by transmission electron microscopy (TEM) investigations shown in [15]. Several stress tensors can be determined by polarized micro-Raman as described in detail in [16].…”