Aerosol synthesis of anatase titanium dioxide nanoparticles for hybrid solar cells

Using an aerosol technique, in which ultrasonically formed droplets of titanium isopropoxide are pyrolyzed, thin films of nanosized anatase titanium dioxide (TiO2) particles are deposited. The size of the particles and the morphology of the films depend on the deposition parameters, i.e., reaction temperature, concentration of the precursor, and gas flow. Under optimal conditions, films can be deposited which consist of stoichiometric anatase TiO2 particles with diameters of 50-300 nm. With these films, solar cells are constructed by spin casting poly(3-octyl)thiophene (P3OT) on top. Devices with a 1-mum film of porous TiO2 and P3OT inside the pores have a short circuit current (I-sc) of 0.25 mA/cm(2), an open circuit voltage (V-oc) of 0.72 V, a fill factor (FF) of 0.35, and an efficiency (eta) of 0.06% under white light illumination (1000 W/m(2)). The efficiency is a factor of 20 higher than that of cells based on flat films of anatase TiO2, whereas the OD for both systems is comparable (flat film equivalent of 60-nm P3OT). The incident photon to current efficiency (IPCE) for the nanostructured solar cell is 2.5% at 488 nm. Devices prepared by adding P3OT during the deposition of the porous TiO2 show the same performance as the cells where P3OT is applied after TiO2 deposition. This shows that penetration of the polymer is quite effective in this system. It is found that P3OT can penetrate these porous TiO2 films as deep as 1 mum.