Effect of Thermal Treatment on Physical Properties of CdTe Thin Films Deposited by a Solution-Based Method

Abstract

The influence of substrate and post-annealing temperature steps on the unique physical, structural, morphology and optical properties of CdTe thin films deposited by a non-vacuum spray process were investigated for solar cells. Scanning electron microscopy (SEM) and X-ray diffraction spectrometer (XRD) were employed to study surface morphologies and structural changes, respectively. It was observed that CdTe films produced at substrate temperature of 130°C had substantially larger grain size and showed denser morphology. Annealing at 130°C–330°C in air caused small grains throughout the surface at random. Annealing at 430°C, however, initiated fusing between grains and produced uniform morphology with an average grain size of about 60 nm. XRD analyses showed that CdTe films deposited at 130°C and then post-annealed at 430°C behaved in the originally strong (111) direction without the formation of secondary CdTeO₃ phase. Optical band gap measurements indicated that the values of CdTe films grown at 130°C and post-annealed at 430°C in ambient condition were about 1.45 eV. All results exhibit 130°C and 400°C to be critical deposition temperature and heat treatment temperature at which physical, optical and structural properties of CdTe thin films start to change.

Keywords:

• Thin film
• solar cell
• solution-based method
• CdTe

Acknowledgment

This research was supported by the Yeungnam University Research Grants in 2009 and the Human Resources Development Program of Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant (No 20104010100580) funded by the Korean Ministry of Knowledge Economy.