The photoconduction mechanisms of screen printed CdS films were investigated by their structure and photoresponse characterizations. It was found that Cl ions were incorporated into the CdS grains and resulted in both the Vcd(Cls)2 complex defect, corresponding to a 0.68 eV trap level, and the Vcd(Cl)s complex defect corresponding to a 0.4 eV level. These values are consistent with those calculated from a chemical quasi-equilibrium approach. In further studies of the CdS films on solar cell applications, these defects were suspected to be responsible for the reduction of Voc, thereby degrading the conversion efficiency of such devices.
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