Effect of annealing on the properties of spray-pyrolysed lead sulphide thin films for solar cell application

Abstract

Annealing is the most important processing parameter perhaps as it directly affects the properties of the thin films. In the present article, lead sulphide thin films composed of (2 0 0) plane-oriented nano-rods were successfully synthesized on glass substrates using spray pyrolysis technique at annealing temperature 350 °C. Films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis by X-ray (EDAX), UV–VIS–NIR spectrometry and two-probe experiments. The X-ray diffraction study confirmed that films exhibiting face-centred cubic structure with a preferred orientation along (2 0 0) plane were independent of annealing temperature. SEM photographs revealed the formation of nano-rods. The possible formation of nano-rods and its dependency on optical and electrical properties were discussed. Chemical composition in terms of atomic ratio of the constituents is determined from EDAX studies. The optical band gap of the lead sulphide thin films was found to decrease from 1.22 to 0.98 eV with an increase in annealing temperature. The electrical conductivity of the films at room temperature was of the order of 10−2 Ω−1 cm−1 with the low activation energy. Results prove that lead sulphide films grown by chemical method appeal its adoptability for potential solar cell applications.