Thermally induced changes of Cu<i>x</i>S films and effect on CdS-Cu<i>x</i>S solar-cell response

Abstract

Changes in the electrical sheet resistance and optical density of copper-sulfide (CuxS) films have been measured as functions of thermal aging in air. It was found that sheet resistance (or bulk resistivity) and optical density (or absorption coefficient) both initially increase with aging, and subsequently decrease. Maximum bulk resistivity and absorption coefficient values, corresponding to the chalcocite phase of CuxS, were found to be about 0.1Ω cm and 5×104 cm−1 (at 1.8 eV photon energy), respectively. CdS/CuxS solar-cell short-circuit current and efficiency were monitored as functions of thermal aging time, degradation being directly related to CuxS sheet resistance. The dependence of sheet resistance on CuxS stoichiometry is discussed. Several possible mechanisms are proposed to account for the observed behavior.