Comprehensive study on the optoelectronic, thermoelectric, and physical properties of amorphous Zn_0.84Fe_0.15B_0.01O thin films

In this study, zinc oxide (ZnO) thin films co-doped with 15 % iron (Fe) and 1 % boron (B) (Zn0.84Fe0.15B0.01O) were successfully synthesized on glass and silicon (Si) substrates using sol-gel-based dip-coating and spray-coating techniques. The optoelectronic, thermoelectric, electrical, and optical transmittance properties of the films were systematically investigated as a function of film thickness (4, 6, 8, and 10 layers). Structural analysis revealed that the produced thin film consisted of an approximately 98 % amorphous matrix with about 2 % nanocrystalline regions exhibiting a wurtzite ZnO structure, with particle sizes ranging from 11 to 350 nm. Photoluminescence (PL) spectroscopy exhibited band-edge emission at 3.26 eV, along with defect-related peaks at 2.42 eV and 1.80 eV. The pronounced intensity of the 1.80 eV peak compared to the UV emission indicates a high density of deep-level defects. Electrical measurements demonstrated a thickness-dependent transition from diode-like to quasi-metallic behavior. This was evidenced by increasing ideality factors from 3.95 to 4.62, decreasing contact barrier heights from 0.608 eV to 0.511 eV, and reduced series resistance values from 23.6 k Omega to 21.0 k Omega. Although the overall optoelectronic performance was limited, the 6-layer sample exhibited the highest solar cell efficiency. In contrast, the 4-layer film displayed promising thermoelectric characteristics, including a Seebeck coefficient of-5600 mu V/K, a power factor of 100 mu W/m & sdot;K2, and a figure of merit (ZT) of 0.006 at 500 K. Additionally, the lowest thermal conductivity (2.3 W/m & sdot;K) was observed in the thickest sample (10-layer), likely due to enhanced structural disorder and phonon scattering. These findings underscore the potential of amorphous 15 %Fe-%1B co-doped ZnO thin films as cost-effective materials for thermoelectric energy harvesting, despite the limitations posed by deep-level defects in photovoltaic and photodetector applications.