V. Švrček 1 , T. Yamanari 1 , D. Mariotti 2 , K. Matsubara 1 M. Kondo 1
1
Research Center for Photovoltaic Technologies, AIST, Tsukuba, 305-8568, JAPAN
2 Nanotechnology & Integrated Bio-Engineering Centre, University of Ulster, UK
Characteristics of microplasma-treated silicon nanocrystals (Si-ncs) . In order to characterize the properties of the microplasma-treated Si-ncs in ethanol, we have measured the Si-ncs photoluminescence (PL) for different microplasma processing times.
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Figure S1 . (a) Photoluminescence (PL) spectra of as-prepared Si-ncs dispersed in ethanol before
(solid line) and after 80 minutes microplasma treatment (dashed line). The inset summarizes PL maxima intensity as a function of microplasma processing time. (b) Absorption spectra of deposited films without sonication of as-prepared Si-ncs/PTB7 (open circles) and microplasma treated Si-ncs/PTB7 (full squares); the solid line is the absorbance corresponding to the film produced with sonicated blend of microplasma-treated Si-ncs/PTB7.
The PL of the ethanol/Si-ncs colloids was measured at 400 nm excitation wavelength using a Xe lamp; PL measurements were taken for as-prepared Si-ncs in ethanol and after every
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~16 minutes of the microplasma treatment. Figure S1a shows PL spectra of as-prepared Si-ncs dispersed in ethanol before and after the microplasma treatment (80 min processing time). Asprepared Si-ncs exhibit room temperature PL; after 80 min of the microplasma treatment, the PL intensity has increased by more than ten times and the peak has red-shifted by about 60 nm. It is believed that an improved surface passivation of the Si-ncs and Si-ncs aggregates has been produced and has enhanced the PL intensity [1, 2]. At the same time, the red shift is ascribed to a replacement of H-terminations with short organic molecules [1, 2]. We have previously reported that the rate of PL increase (inset of figure S1a) is directly related to the concentration of the Sincs dispersed in ethanol [2].
Similar absorption features have been observed for the nanocomposite films which were produced with as-prepared Si-ncs and microplasma-treated Si-ncs (figure S1b, spectra with symbols). In all cases, the spectra are mostly characterized by the polymer superior absorption properties which show strong absorption from 550 nm to 750 nm [3] and relatively weak absorption from 300 nm to 500 nm. The only minor difference is a slightly lower absorption below 600 nm for the composites with microplasma-treated Si-ncs (full squares) compared to the samples that used as-prepared Si-ncs (open circles).
Effect of sonication on surface morphology of the deposited blends . In support of our analysis, figure S2 shows typical scanning electron microscope (SEM; Hitachi S-4300) and atomic force microscope (AFM; SiII Nanotechnology, Nano Navi E-sweep) images of the blends: (a) as-prepared Si-ncs/PTB7 and (b) microplasma-treated Si-ncs/PTB7 both without sonication.
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Figure S2 . Typical scanning electron microscope image of the blends: (a) as-prepared Si-ncs, (b) microplasma-treated Si-ncs. Images in (c) and (d) show the corresponding atomic force microscope images, respectively.
From the SEM images (figures S2a-b), the surface morphology of the three films seems to have similar features in all cases. However, a more detailed AFM analysis showed clear differences (Figures S2c-d). After microplasma treatment the surface morphology presented
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reduced roughness. The RMS value decreased by almost a factor of 10, from 6.8 nm for asprepared Si-ncs (figure S2c) to 0.6 nm for microplasma-treated Si-ncs (figure S2d). This is likely due to fact that the Si-ncs become better separated after the microplasma treatment [2].
References
[1] V. Švrček, D. Mariotti, M. Kondo, Appl. Phys. Lett .
2010 , 97, 161502.
[2] D. Mariotti, V. Švrček, J. W. J. Hamilton, M. Schmidt, M. Kondo, Adv. Funct. Mater. 2012 , ,
22 , 954.
[3] Y.Liang, Z. Xu, J. Xia, S.T. Tsai, Y. Wu, G. Li, C. Ray, and L. Yu, Adv. Mater. 2010 , 22,
E135.
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