Flexible tetra-carboxyphenyl porphyrin thin films for optoelectronic devices: Structural, optical and electrical characteristics

Electronic devices based on flexible plastic substrates have much attention in the electronics future. A comprehensive analysis was performed to investigate the impact of thickness on vacuum-thermally produced tetra-carboxyphenyl porphyrin (TCPP) thin films on flexible indium tin oxide (ITO)/polyethylene terephthalate (PET) substrates. An X-ray diffraction (XRD) pattern demonstrated that the thin films had an amorphous structure. Atomic force microscopy (AFM) images were exposed, and average roughness (Ra), increased with layer thickness from 2.72 to 4.95 nm. Characteristic vibrations of intermolecular bonds in TCPP were confirmed using Fourier-transform infrared spectroscopy (FT-IR). Optical characterization studies indicated that the thin films exhibited an indirect allowed transition, as determined by the optical band gap (
). Furthermore, it was observed that the values of
was decreased from 2.67 to 2.44 eV as the thickness of the thin films increase from 90 nm to 320 nm. The dispersion parameters at normal dispersion were calculated as a function of film thickness. The calculated third-order nonlinear susceptibility χ (3) and nonlinear refractive index n2 were found to be in the order of ∼10−10 and∼10−9 esu, respectively within the photon energy range of 0.5–4 eV. The photoresponse of Au/TCPP/ITO/PET diodes was evaluated under varying illumination conditions, revealing a photoresponsivity of 3.58 A/W, specific detectivity (D∗) of 3.02 × 1010 Jones, photosensitivity (PS) of 81.63 %, linear dynamic range (LDR) of 5.12 dB and external quantum efficiency of 8.05 % at -1V and 100 mW/cm2. Finally, the conduction mechanism of the Au/TCPP/ITO/PET diode was investigated under forward bias voltage conditions. These findings highlight the potential of TCPP/ITO/PET thin films for flexible optoelectronic applications, particularly in nonlinear optical devices and photodiodes.