Recombination and transport in microcrystalline pin solar cells studied with pulsed electrically detected magnetic resonance J. Behrends a , A. Schnegg a , C. Boehme a,b , S. Haas c , H. Stiebig c , F. Finger c , B. Rech a,c , K. Lips a, * a Hahn-Meitner-Institut Berlin, Abt. Silizium-Photovoltaik, Kekule ´str. 5, D-12489 Berlin, Germany b University of Utah, Physics Department, 115S 1400E, Salt Lake City, Utah 84112, USA c Forschungszentrum Ju ¨ lich, Institut fu ¨ r Energieforschung-Photovoltaik, 52425 Ju ¨ lich, Germany Available online 17 March 2008 Abstract An analysis of spin-dependent processes in microcrystalline silicon (lc-Si:H) pin solar cells is presented using pulsed electrically detected magnetic resonance (pEDMR). In this first study it is shown that by modulating the morphology of the n-type contact layer from amorphous to microcrystalline, pronounced changes in the pEDMR spectra may be observed. Due to the fact that pEDMR allows a deconvolution of the spin-dependent signals in time as well as in magnetic field domain, we were able to significantly reduce the com- plexity of the spectra compared to conventional EDMR. In the samples containing amorphous n-type contact layers we found signals from shallow localized conduction band tail states and phosphorous donor states. Upon replacement of this layer by its microcrystalline counterpart both signals disappeared. Possible spin-dependent transport mechanisms involving paramagnetic states in the various layers are discussed in view of sign and time evolution of the associated pEDMR signals. Ó 2007 Elsevier B.V. All rights reserved. PACS: 72.20.Ee; 72.20.Jv; 72.25.Dc; 76.90.+d Keywords: Solar cells; Photovoltaics; Conductivity; Defects; Microcrystallinity; Electron spin resonance 1. Introduction Solar cells made from hydrogenated microcrystalline sil- icon (lc-Si:H) are superior to crystalline silicon (c-Si) cells with regard to material consumption and cost effectiveness. Unfortunately, state-of-the-art lc-Si:H suffers from an inferior electronic quality compared to the crystalline coun- terpart. It consists of small crystalline grains with dimen- sions of up to a few 10 nm, which are surrounded by an amorphous silicon (a-Si:H) region. It is assumed that the a-Si:H region and the grain boundaries induce dangling bonds and tail states in the band gap of lc-Si:H which dete- riorate the electronic properties through trapping and recombination [1]. Quantitative as well as structural infor- mation about such states in lc-Si:H powder samples were obtained by electron spin resonance (ESR) [1,2]. Neverthe- less, it remains unclear if such information can be directly transferred to lc-Si:H incorporated in solar cells since the boundary conditions for layer growth are different. Unfor- tunately, ESR studies on state-of-the-art lc-Si:H solar cells are hampered by the low detection sensitivity of ESR and by the fact that the contact layers induce additional ESR signals [3]. To overcome this limitation, we applied pulsed electrically detected magnetic resonance (pEDMR), a novel technique recently developed at HMI [4,5], which is able to detect paramagnetic states that influence transport and recombination through spin-dependent processes (for a review see the Mott lecture given by W. Fuhs in this issue). pEDMR combines the benefits of conventional EDMR [6], 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.09.086 * Corresponding author. E-mail address: lips@hmi.de (K. Lips). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 354 (2008) 2411–2415