An annealing-free anatase TiO2 nanocrystal film as an electron collection layer in organic solar cells

Anatase TiO2 film, which is traditionally fabricated by high-temperature annealing of TiOx precursors, has been widely used as an electron collection layer in photovoltaics. In order to avoid the undesired high temperature treatment, in this work, we developed a convenient and moderate procedure to fabricate anatase TiO2 nanocrystal films at room temperature. Ultrafine, clean and high-quality anatase TiO2 nanocrystals have been pre-prepared in a simple solvothermal route and subsequent spin-coating of the nanocrystal dispersion provides a well formed TiO2 nanocrystal film without any further thermal treatment. The characteristics of the TiO2 nanocrystal film, in terms of crystallization phase, film morphology, optical and electronic properties, have been carefully studied, and then a typical [ITO/TiO2/P3HT:PCBM/MoO3/Ag] inverted photovoltaic device using TiO2 nanocrystals as the ECL has been fabricated and exhibits a comparable power conversion efficiency (PCE) of 3.35% to that of the conventional device (3.39% PCE).