Structural, optical and electrical characterization of gadolinium and indium doped cadmium oxide/p-silicon heterojunctions for solar cell applications

Abstract

Gadolinium and indium co-doped CdO thin films were prepared by a pulsed laser deposition method. The XRD and XPS results indicated that Gd³⁺ and In³⁺ ions occupied locations in the interstitial positions and/or Cd²⁺-ion vacancies in the CdO lattice. The FESEM images showed that the films were homogeneous and consisted of nanograins with a size range of 23–40 nm. The optical band gap of the CdO thin films can be engineered over a wide range of 2.72–3.56 eV by introducing Gd and In dopants. Such transparent semiconducting Gd and In co-doped CdO films were then grown on p-type Si substrates to fabricate n-CdO/p-Si heterojunction devices. The important junction parameters such as the series resistance (R_s), ideality factor (n) and Schottky barrier height (Φ_b) were determined by analysing different plots from the current density–voltage (J–V) characteristics. The obtained results indicated that the electrical properties of the heterojunction diodes were controlled by the dopant concentration. The p-Si/n-Cd_1−x−yGd_xIn_yO heterojunction diode showed the best values of open circuit voltage, V_oc = 1.04 V and short circuit current density, J_sc = 11.4 mA cm⁻² under an illumination intensity of 100 mW cm⁻², which was suitable for solar cell applications.