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.