The effects of inclusion of iodine in CdTe thin films on material properties and solar cell performance

Abstract

CdTe thin films were potentiostatically electrodeposited from a non-aqueous electrolytic bath containing ethylene glycol. In order to dope the CdTe using an n-type dopant according to a proposed new model, varying concentrations of iodine were added into the electrolytic bath. The resulting materials were studied for structural, morphological, optical and electrical properties. Structural analysis indicated the formation of CdTe layers without other possible phases at a concentration of similar to0.05 M of iodine in the bath. Optical absorption measurements have yielded a direct band gap value of 1.42 +/- 0.03 eV without showing any noticeable changes of the energy gap. Inclusion of iodine in CdTe layers have increased the electrical conductivity by a factor of 5, indicating positive n-type doping effects. The diodes of FTO/CdS/CdTe/Au structures showed improved current-voltage characteristics indicating the presence of a high potential barrier of 1.20 eV with low ideality factors around 1.40. These results demonstrate a considerable reduction of active recombination and generation centres from the structure. Although the fill factors observed are low, for the studied batches in this project, remarkable improvement of short-circuit current densities over 40 mA cm(-2) were observed together with open circuit voltage values in the range 500-700 mV. Capacitance-voltage measurements indicate a formation of a fully depleted device, desirable for photovoltaic conversion. (C) 2002 Published by Elsevier Science B.V.