Chemical, structural and photovoltaic properties of graded CdS_xSe_1−x thin films grown by chemical bath deposition on GaAs(100)

Cd(S,Se) films are direct band gap ternary semiconductors that can harvest photoenergy in an energy range from 2.42 eV (CdS) to 1.74 eV (CdSe). Growth of these films using chemical bath deposition (CBD) is advantageous due to low production costs and the ability to easily control the initial bath composition. In this work, the chemical, structural and photovoltaic properties of Cd(S,Se) solid solution thin films deposited on GaAs(100) are presented. Chemically graded films were formed by controlling the initial anion concentrations in the bath, which affect the nucleation and growth of the films. The films are polycrystalline in nature, with a thin zinc blende layer formed directly on the GaAs substrate, on top of which a highly oriented nano-columnar layer of wurtzite Cd(S,Se) is obtained. The photovoltaic properties of CBD CdS films show 2.9% conversion efficiency, while increasing the selenide content in the films decreases the conversion efficiency.