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

Doping, compensation and photovoltaic performance have been investigated ill 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 10(17) -1.5 x 10(19) cm(-3), the maximum net acceptor concentration is only in the order of 10(14) cm(-3), as determined by capacitance-voltage characteristics. Admittance spectroscopy revealed shallow traps at 0.055 eV which were attributed to As,; its compensation by Cd(i) is discussed. Formation of the alloy CdS(x)Te(1-x) is linked to deep levels at E(V+)similar to 0.55 eV and E(V+)similar to 0.65 eV. Limits to the diffusion of photo-generated carriers were considered to be important ill determining photovoltaic performance rather than carrier lifetime. Prospects for optimizing the performance Of Such co-doped MOCVD-grown devices are discussed. (C) 2009 Elsevier B.V. All rights reserved.