Low temperature crystalline titanium dioxide by atomic layer deposition for dye-sensitized solar cells

Low temperature processing of dye-sensitized solar cells (DSC) is crucial to enable commercialization with low-cost, plastic substrates. Prior studies have focused on mechanical compression of premade particles on plastic or glass substrates, however, this did not yield sufficient interconnections for good carrier transport. Furthermore, such compression can lead to more heterogeneous porosity. To circumvent these problems, we have developed a low temperature processing route for photoanodes where crystalline TiO2 is deposited onto well-defined, mesoporous templates. The TiO2 is grown by atomic layer deposition (ALD) and the crystalline films are achieved at a growth temperature of 200 °C. The ALD TiO2 thickness was systematically studied in terms of charge transport and performance to lead to optimized photovoltaic performance. We found that a 15 nm TiO2 overlayer on an 8 μm thick SiO2 film leads to a high power conversion efficiency of 7.1% with the state-of-the-art zinc porphyrin sensitizer and cobalt bipyridine redox mediator.