Effective two-step chemical deposition for homogeneous lead sulfide thin films on a flexible polymer substrate

Chalcogenide PbS has been extensively studied as a p-type semiconductor material for various optoelectronic devices. Here, an effective two-step chemical bath deposition process is introduced to achieve dense microstructure of PbS thin films specifically for a flexible polyethylene terephthalate (PET) substrate. Three different types of substrates, such as Cu foils, glass substrate and PET, were initially examined to compare different crystal growth behaviors of PbS thin films depending on the choice of substrate. Only the PET substrate demonstrated an unacceptable coverage of films even with the extended deposition due to a retarded growth presumably with more scattered initial distribution of nuclei. Conclusively, two-step deposition processing at a low temperature of 40 °C for the PET substrate was successful in achieving homogeneous microstructures with proper bandgap and film thickness. As a promising result, the 60 min plus 60 min-double depositions at 40 °C produced an ideal bandgap of ~1.58 eV with a proper film thickness of ~200 nm.