Characterization of nanoporous TiO2 films prepared by sol-gel method

Nanoporous TiO2 films as a key component in dye sensitized and extremely thin absorber (ETA) solar cells were prepared by the sol-gel method using spin-coating and spray pyrolysis deposition techniques. The precursor sol contained titanium (IV) isopropoxide, acetylacetone and polyethylene glycol (PEG) in ethanol. Glass and n-type Si (100) were used as substrates. SEM, XRD and FT-IR were used to study the effect of the PEG concentration in the precursor solution as well as different annealing routes on the film composition and structural properties. Crystalline films with anatase structure could be grown by the spray technique at 500 degrees C. Post-annealing at 500 degrees C increases the crystallite size (from 5 to 9 nm) and results in an average pore size around 40 nm. A film thickness of about 2.3 mu m is attained using 50 spray pulses. In spin coated films the formation of Ti-O-Ti anatase bonds is observed after annealing at 450 degrees C. Crystalline films can be prepared by annealing at temperatures above 700 degrees C. Surface morphology and pore size of spin coated films are controlled by the amount of PEG in the sol. The film thickness is around 120 nm after three coating cycles.