C– V calculations in CdS/CdTe thin films solar cells

Abstract

Polycrystalline thin film CdS/CdTe heterojunction solar cells are important candidates for large scale photovoltaic applications. In this work we use a C– V (capacitance vs. voltage) theoretical method for the determination of the interface charge density σ and band discontinuity Δ Ev of the CdS/CdTe heterojunction. The methodology is based on three cardinal equations: i) line up of the bands relative to the common Fermi level (at equilibrium) or the quasi-Fermi level (when voltage is applied), ii) charge neutrality and iii) the total capacitance of the heterostructure. We used CdS/CdTe solar cells, grown in our laboratory by the chemical bath deposition (for CdS film) and the close space vapor transport (for CdTe film) techniques. The interface parameters σ, and Δ Ev are determined from C– V fitting between the calculated and the measured curve. The methodology presented in this study is general and can be applied to semiconductor–semiconductor and semimetal–semiconductor heterojunctions.