Structural characterizations and photoelectric performance of non-crystalline boron subphthalocyanine chloride films/FTO for photodiode applications

A thin film of Boron subphthalocyanine chloride (B-subPcCl) has been deposited with different thicknesses, up to 300 nm, on the conductive fluorine-doped tin oxide (FTO) substrates using an evaporating coating unit. The structure of the fabricated film has been studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD confirmed that B-subPcCl films are an amorphous material, and AFM showed that the fabricated thin films' grain sizes increased from 123.5 to 206.5 nm as the film thickness from 76 to 300 nm. The optical properties such as reflectance, transmission, absorption index, and refractive index have been characterized by the analysis of the spectrophotometric measurements. As a result of the thin film thickness increase up to 300 nm, the energy bandgap was decreased by about 10%. The refractive index shows the lowest value at 1680 nm due to the polarization decrease. The I–V characteristics of the FTO/B-subPcCl/Au photodiode were investigated in the dark and under various light illumination intensities. The rectification ratio of our diode was 199 and 59 in dark and light, respectively. The thermionic emission theory was used to calculate the main diode parameters. The current architecture, FTO/B-subPcCl/Au, demonstrated a good light response, with estimated values of responsivity of about 4.2 × 10⁻⁶ A/W at -1 V and illumination intensity of 80 mW/cm².