Tuning the chemistry of Al source to control the Al release rate in chemical bath deposition of aluminum-doped zinc oxide

• Al-doped ZnO (AZO) thin film as TCO was prepared via the CBD method at 85 °C. • The work identifies the crucial role of the Al precursor in achieving AZO thin films with tailored optical and electrical properties. • Al(OH) 3 ​ precursor enables controlled Al doping, leading to improved film properties. • Controlling crystalline plane growth with ammonium citrate achieved high transmittance of ∼90 and 80 with sheet resistances of 62 and 30,Ω/□ at 40- and 46-min deposition times respectively. Chemical bath deposition (CBD) is a versatile and relatively simple technique used to grow thin films of a wide range of materials, such as metal chalcogenides and oxides. Achieving precise control over the film's thickness and composition can sometimes be challenging. This study focuses on the investigation of Al precursor combined with deposition time to enable the gradual addition of Al dopant and achieve a dense Al-doped zinc oxide (AZO) qualified thin films. The controlled release of the dopant, “Al”, is an important factor in achieving high-quality layers. The Al(NO 3 ) 3 , Al(OH) 3 , and C 4 H 7 AlO 5 as the Al precursors with concentrations of 1, 2, 3, and 4 mM, were investigated. The AZO films deposited with different sources of Al are characterized for their structural, surface morphological, electrical, and optical properties. Increasing the nitrate source concentration, despite its positive effect on the transparency of the layers, leads to an increase in sheet resistance, while the acceptable sheet resistance and transparency values were achieved, these factors ​​do not show improvement with increasing the acetate source concentration. Also, a non-uniform deposition related to residual organic species was observed. The doping process with Al(OH) 3 precursor was carried out gradually due to its low solubility in the chemical bath, leading to the appropriate concentration profile. Increasing the Al(OH) 3 concentration from 1 to 3 mM leads to improvement of sheet resistance from ∼167 to ∼31 Ω/◻, while the optical transparency shows about 10 % decrease at 550 nm. In addition, by controlling the growing crystalline planes using ammonium citrate (C 6 H 11 NO 7 ), a sheet resistance of 62 and 30 Ω/◻ and high transmittance of ∼90 % and 80% were achieved for deposition times of 46 and 52 min, respectively.