Doping levels, trap density of states and the performance of co-doped CdTe(As,Cl) photovoltaic devices

Abstract

Doping, compensation and photovoltaic performance have been investigated in all-metal-organic vapour-phase deposition (MOCVD) grown CdTe/CdS solar cells that were co-doped with arsenic and chlorine. Although arsenic chemical concentration is in the range of 1017-1.5×1019 cm-3, the maximum net acceptor concentration is only in the order of 1014 cm-3, as determined by capacitance-voltage characteristics. Admittance spectroscopy revealed shallow traps at 0.055 eV which were attributed to AsTe; its compensation by Cdi is discussed. Formation of the alloy CdSxTe1-x is linked to deep levels at EV+∼0.55 eV and EV+∼0.65 eV. Limits to the diffusion of photo-generated carriers were considered to be important in determining photovoltaic performance rather than carrier lifetime. Prospects for optimizing the performance of such co-doped MOCVD-grown devices are discussed. © 2009 Elsevier B.V. All rights reserved.