Elucidation the effectiveness of acridine orange as light-harvesting layer for photosensing applications: Structural, spectroscopic and electrical investigations

Abstract

In this research, acridine orange, AO, bio-photosensitive thin films are prepared using vacuum thermal evapo- ration technique for optoelectronic applications. First, the crystal structure of the deposited films compared to powder is investigated using the XRD technique. Next, the surface morphology of the deposited AO thin film is characterized using the FESEM technique giving rise to a uniform, homogeneous, and granular polycrystalline film. The amplitude and spatial roughness parameters of the film are estimated. Furthermore, the optical properties of the deposited AO thin film are spectrophotometrically characterized in the range from UV to NIR. The recorded absorbance, transmittance, and reflectance showed high UV and visible absorption characteristics with a direct energy gap of ~2.238 eV. The optical constants, including refractive index and extinction coeffi- cient, are found, and the dispersion behavior is analyzed using the one-oscillator model for estimating the oscillator and dispersion energies. The dielectric function and dielectric relaxation time of AO thin film are interpreted in detail. In addition, an organic/inorganic heterogeneous junction based on Ag/AO/p-Si/Al is fabricated and electrically evaluated using the current-voltage relation. The fabricated heterojunction shows a rectification behavior of ideality factor, barrier height, and rectification ratio ~2.09, 0.707 eV, and 176, respectively. The charges dynamics mechanism in terms of band diagram and the density of interface states profile are analyzed. Eventually, the photoresponse of the engineered heterojunction is evaluated under the illumination of intensities that varies from 20 mW/cm2 to 100 mW/cm2 . The fabricated photosensor showed a high stable performance with responsivity, specific detectivity, linear dynamic range, and ON/OFF ratio of about 68.4 mA/W, 1.11 × 1010 Jones, 69.3 dB, and 108.4, respectively. The photoresponse performance of the present device is considered more efficient and stable than many other organic/inorganic photosensors.