PVP-SiO₂ and PVP-TiO₂ hybrid films for dielectric gate applications in CdS-based thin film transistors

We report a simple solution process to deposit organic-inorganic poly (vinyl phenol) (PVP)–SiO₂ and PVP-TiO₂ hybrid films. The spin dropped hybrid films were prepared at low-temperature and their main properties were studied by TGA, FE-SEM, AFM, FTIR, XPS and contact angle measurements. The results show that the surface of the PVP-SiO₂ and PVP-TiO₂ hybrid films is smooth with very low surface roughness of 0.25 and 0.51 nm, and surface energy of 48.4 and 40.1 mJ/m², respectively. The electrical properties of the hybrid films, measured on MIM devices, show low leakage current density under 10⁻⁷ A/cm² and dielectric constant of 5 and 4.6 at 1 kHz, respectively. The hybrid films were used as gate dielectric in solution-processed CdS thin film transistors (TFTs), showing diverse performance. The CdS/PVP-SiO₂ devices showed high mobility of 18 cm²/Vs, on/off current ratio of 10⁴, low threshold voltage of 0.6 V and subthreshold swing of 0.25 V/dec. Whereas, the corresponding values for the CdS/PVP-TiO₂ ones were 0.45 cm²/Vs, 10⁴, 1.9 V and 1.25 V/dec, respectively. The lower electrical performance of the CdS/PVP-TiO₂ devices was attributed to the mismatching surface energies between the surfaces of the dielectric and semiconductor layers, and to the influence of a large number of trapped charges at this interface.