CdS thin films deposited onto a highly transparent co-polyamide

Cadmium sulfide (CdS) was deposited onto a co-polyamide (DHTH) substrate by two different techniques: chemical bath deposition (CBD) and spray pyrolysis (SP). The synthesis of the DHTH resulted from the combination of two bulky pendant groups and a hexafluoroisopropylidene, C(CF₃)₂, by direct polycondensation. Thermal stability, optical transmittance, and mechanical properties of the DHTH were measured before the CdS deposition. The DHTH substrates exhibited a high transmittance (> 82%) for wavelengths above 400 nm, an elastic modulus of 2.9 GPa, and T_g of 318 °C. CdS was deposited by CBD at 80 °C, using cadmium chloride, potassium hydroxide, ammonium nitrate, and thiourea as chemical reagents. For the SP deposition, cadmium chloride and thiourea were used as chemical reagents while the substrate temperature was fixed to 300 °C. CdS thin films of good transparency and adherence were obtained. The bandgap energy of the deposited CdS films was estimated as 2.32 eV and 2.38 eV, for CBD and SP techniques, respectively. The rms roughness of the CdS was 164 nm for the films grown by CBD and 37 nm for those grown by SP. Finally, the X-ray diffraction confirmed cubic and hexagonal crystalline structures for the CdS grown by CBD and SP, respectively, which agrees with the structures corresponding to low (CBD)- and high (SP)-temperature techniques. The CdS physical properties confirmed the deposition of a semiconducting thin film onto a home-synthesized high-transparency polymer substrate by two different low-cost and scalable techniques, representing an important advancement on the development of new material systems for optoelectronic applications.