Mapping boron in silicon solar cells using electron energy-loss spectroscopy

Martial Duchamp (Author), András Kovács (Author), Shima Kadkhodazadeh (Author), Chris Boothroyd (Author), Ramona Valentina Mateiu (Author), Bas B. Van Aken (Author), Simon B. Newcomb (Author), Rafal E. Dunin-Borkowski (Author)

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Abstract

Amorphous silicon solar cells typically consist of stacked layers deposited on plastic or metallic substrates making sample preparation for transmission electron microscopy (TEM) difficult. The amorphous silicon layer - the active part of the solar cell - is sandwiched between 10-nm-thick n- and p-doped layers. The typical boron concentration in the p-doped layer is ~10^21cm -3 and should not exceed 1017cm-3 in the neighbouring intrinsic (i) layer [1], where it acts as a charge recombination centre and decreases the internal electric field [2]. The detection of low boron concentrations with high spatial resolution using TEM is highly challenging [3]. Recently, scanning TEM (STEM) combined with electron energy-loss spectroscopy (EELS) and spherical aberration-correction has allowed the direct detection of dopant concentration of 10^20cm-3 in 65-nm-wide silicon devices [4]. Here, we prepare TEM samples by focused ion beam milling in order to map the boron distribution across a 200-nm-thick n-p amorphous silicon junction using energy-filtered TEM and EELS spectrum acquisition. EELS line scans are used to detect boron concentrations as low as 10^20cm-3. We also use monochromated EELS to measure changes in the energies of plasmon peaks in the low loss region [5]. We use these approaches to characterize both a thick n-p junction and the 10-nm-thick p-doped layer of a working solar cell. [1] U. Kroll, C. Bucher, S. Benagli, I. Schönbächler, J. Meier, A. Shah, J. Ballutaud, A. Howling, Ch. Hollenstein, A. Büchel, M. Poppeller, Thin Solid Films 451 (2004) 525 [2] B. Rech, H. Wagner, Applied Physics A 69 (1999) 155 [3] C.B. Boothroyd, K. Sato, K. Yamada, Proceedings of the XIIth international congress for electron microscopy, ed LD Peachey and DB Williams (San Francisco Press, San Francisco, 1990) 80 [4] K. Asayama, N. Hashikawa, K. Kajiwara, T. Yaguchi, M. Konno, H. Mori, Applied Physics Express 1 (2008) 074001 [5] V. Olevano, L. Reining, Physical Review Letters 86 (2001) 5962
Original languageEnglish
Publication date2010
Publication statusPublished - 2010
Event7th Workshop on EELS/EFTEM - Zürich, Switzerland
Duration: 27 Oct 201029 Oct 2010
Conference number: 7

Workshop

Workshop7th Workshop on EELS/EFTEM
Number7
CountrySwitzerland
CityZürich
Period27/10/201029/10/2010

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