Room temperature synthesis of BiOBr_1- I thin films with tunable structure and conductivity type for enhanced...

The surface states of semiconductors determine the semiconductor type. Although BiOCI, BiOBr and BiOI all belong to the bismuth oxyhalide semiconductor family and have similar crystal structures and electronic structures, they exhibit different conductivity types due to their respective surface states. In this paper, a modified successive ionic layer adsorption and reaction (SILAR) method was developed to fabricate I-doped BiOBr_1- I nanosheet array films on FTO substrates at room temperature for the first time. Interestingly, the properties of p-type BiOBr were changed by doping an appropriate amount of iodine into a BiOBr film to form an n-type BiOBr_1- I thin film. The I-doped BiOBr_1- I (x = 0.2, 0.4, 0.5) nanosheet arrays had a perfect single-crystal structure, and the dominant growth plane was (110). A higher doping amount of I led to a darker colour of the BiOBr_1- I film and a redshift of the absorption wavelength; consequently, the bandgap value changed from 2.80 eV to 1.85 eV. The highest short-circuit current and open-circuit voltage of the solar cell based on BiOBr_0.5I_0.5 film could reach 1.73 mA cm^-2 and 0.55 V, which was considered to be attributed to the effective light absorbance, long photogenerated charge lifetime and sufficient charge separation in the BiOBr_0.5I_0.5 film.