Experimental evidence of boron induced charged defects in amorphous silicon materials

We present an experimental proof of the existence of charged defects related to boron diffusion at the pi interface of single junction amorphous silicon solar cells. Two different test devices were manufactured substituting the intrinsic absorber layer of a standard p-i-n structure with a boron lightly doped layer or a microcompensated region. Presence of trap states lying around 0.3-0.4 eV above the valence band was demonstrated through spectral photocapacitance response under medium infrared radiation and through capacitance versus frequency measurements that show the typical response of trapping kinetics process. Differences in the experimental results between our test devices and standard p-i-n solar cells show that boron atoms are the main cause of charged defect formation. (C) 1999 Elsevier Science S.A. All rights reserved.