Determination of defect distribution in a Ga-rich ZnO/CdS/Cu (In, Ga) $Se_2$ solar cell by admittance spectroscopy

Abstract

This article presents a study on the energy distribution of defects in efficient thin film ZnO/CdS/Cu(In,Ga)$Se_2$ heterojunction solar cell by the use of admittance spectroscopy. The capacitance spectra of the device has been analyzed using a model based on the existence of a homogeneous distribution of bulk acceptors in the absorber Cu(In,Ga)$Se_2$ layer. This model reveals an emission from a distribution of hole traps centered at an activation energy of about 300 meV with a defect density of $1.2xl0^{17} eV^{-1}cm^{-3}$. The band gap of the absorber layer is estimated to be about 1.46 eV which corresponds to a Ga content of about $xapprox 0.7$ with x the ratio Ga/(Ga+In).