The effect of processing conditions on the structural morphology and physical properties of ZnO and CdS thin films produced via sol-gel synthesis and chemical bath deposition techniques

Shahzad Salam, Mohammad Islam, Mahboob Alam, Aftab Akram, Mujtaba Ikram, Asif Mahmood, Majid Khan and Mohammad Mujahid

Abstract

Cadmium sulfide (CdS) and zinc oxide (ZnO) are used in thin film solar cells as buffer layer and transparent conducting oxide, respectively. The effect of annealing conditions on the morphology and physical properties of CdS and ZnO films prepared using chemical bath deposition and sol–gel synthesis techniques, respectively, was investigated. CdS films obtained from the chemical bath deposition (CBD) process were found to be polycrystalline with dense granular morphology. Electrical characterization of the films annealed at 400 °C for 10 min yielded values of 2.2×10⁻³ Ω cm and 8.3×10¹² cm⁻³ for resistivity and carrier concentration, respectively. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) studies of intrinsic zinc oxide (i-ZnO) films revealed flake-like morphology and transformation of the as-deposited amorphous structure into a hexagonal wurtzite crystal structure upon annealing at 500 °C for 2 h. Optical and electrical characterization results showed that such films had ~80% transmittance and resistivity values as low as 6.4×10² Ω cm. These films are being explored for fabrication and testing of copper-indium-gallium-(di)selenide (CIGS) thin film solar cells obtained from simple, cost-effective, solution-based synthesis routes