Analysis of grain orientation and defects in Sb_2Se_3 solar cells fabricated by close-spaced sublimation

摘要

The performance of a superstrate TiO2/Sb2Se3 solar cell, fabricated by close-spaced sublimation technique (CSS), was improved after the deployment of a seed layer. The seed layer caused columnar Sb2Se3 film growth with texture coefficient analysis (TC) showing increased presence of crystal planes, which are inclined towards the [001] crystal direction. Given the highly anisotropic properties of Sb2Se3, preferential growth of (Sb4Se6)(n) ribbons along the [001] direction is best suited for effective charge collection. Hence, grain orientation of Sb2Se3 films was studied more closely via measurement of pole figures by XRD and orientation distribution maps by electron backscatter diffraction (EBSD). Although the measurements did not reveal strong preferred orientation, it was observed that the columnar Sb2Se3 growth enhanced texture along the [001] direction. Temperature-dependent admittance spectroscopy (TAS) and capacitance-voltage (CV) profiling were performed on the seed-assisted TiO2/Sb2Se3 solar cell to evaluate carrier density and deep defects in the Sb2Se3 absorber. TAS study revealed a deep defect with activation energy of 0.39 eV. CV profiles indicated that the density of defects could be as high as 10(17) cm(-3), which needs to be addressed by post-deposition treatments.