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

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

Topics

• impedance spectroscopy
• polymer
• amorphous
• grinding
• milling
• focused ion beam
• transmission electron microscopy
• Silicon
• Boron
• electron energy loss spectroscopy