Field modulation in Na-incorporated Cu(In,Ga)Se2 (CIGS) polycrystalline films influenced by alloy-hardening and pair-annihilation probabilities

Research Institute for Solar and Sustainable Energies (RISE), Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro, Buk-gu, Gwangju 500-712, South Korea. .
Nanoscale Research Letters (Impact Factor: 2.78). 11/2011; 6(1):581. DOI: 10.1186/1556-276X-6-581
Source: PubMed

ABSTRACT The influence of Na on Cu(In,Ga)Se2 (CIGS) solar cells was investigated. A gradient profile of the Na in the CIGS absorber layer can induce an electric field modulation and significantly strengthen the back surface field effect. This field modulation originates from a grain growth model introduced by a combination of alloy-hardening and pair-annihilation probabilities, wherein the Cu supply and Na diffusion together screen the driving force of the grain boundary motion (GBM) by alloy hardening, which indicates a specific GBM pinning by Cu and Na. The pair annihilation between the ubiquitously evolving GBMs has a coincident probability with the alloy-hardening event.PACS: 88. 40. H-, 81. 10. Aj, 81. 40. Cd.

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Available from: Yonkil Jeong, Sep 28, 2015
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    • "The graded bandgap-induced back-surface field effect, which arises because of the composition dependence of the Ga/(Ga + In) ratio, leads to an increase in the open-circuit voltage (V OC ), fill factor, and short-circuit current density (J SC ) [25] [26]. Na incorporation in CIGS films affects their grain growth and preferred orientation, resulting in small grain size and an increase in V OC [27]. Thus, the current level of understanding of CIGS films is fairly high. "
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    ABSTRACT: The results for laser-induced breakdown spectroscopy (LIBS) measurement of thin Cu films (1 μm) on soda-lime glass (SLG) substrates with and without a supporting thin Mo layer (1 μm) are reported. The ablation was carried out using a nanosecond Q-switched Nd:YAG laser (λ=1064 nm, τ=4 ns, spot diameter=50  μm, top-hat profile) in the laser fluence range of 19.16-65.97 J/cm(2). It was found that, under the same laser irradiance conditions, the depth and morphology of ablation craters produced with and without the Mo layer were completely different. The electron number densities of the plasma from the two samples calculated from the measured LIBS spectra differed by a factor of 4 as 4.1×10(17) cm(-3) (Cu/Mo/SLG) and 17.7×10(17) cm(-3) (Cu/SLG), which was attributed to the matrix effects resulting from ionization of Na atoms diffused into the Mo layer. It is demonstrated that a nanosecond-laser-based LIBS is applicable for the characterization and composition analysis of thin film layers of a few micrometer thickness on glass substrates, especially for the measurement of Na contents of each layer.
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    ABSTRACT: This paper reports that selective removal of a CuIn 1−x Ga x Se 2 (CIGS) thin film on a Mo-coated glass substrate can be achieved with no edge melting or damage of the Mo layer using a nanosecond Nd : YAG laser with a wavelength of 1064 nm. It is shown that the two crucial parameters that determine the possibility of clean removal of only the CIGS layer are Ga concentration of the CIGS film and laser fluence. For CIGS films with Ga/(Ga+In) ratio greater than about 0.2 for which the band gap energy is close to or over the photon energy (1.17 eV), laser-induced thermal expansion proved to be the mechanism of film removal that drives an initial bulging of the film and then fracture into tens of micrometre sized fragments as observed in in situ shadowgraph images. The fracture-type removal of CIGS films was further verified by scanning electron micrographs of the craters showing that the original shapes of the CIGS polycrystals remain intact along the crater rim. A numerical simulation of film temperature under the irradiation conditions of selective removal was carried out to show that the magnitude of induced thermal stress within the film closely agreed to the yield strength of the CIGS thin film. The results confirmed that a nanosecond laser could be a better choice for P2 and P3 scribing of CIGS thin films if process conditions are properly determined. (Some figures may appear in colour only in the online journal)
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