In this paper we focus on the effect of carboxylated thiophene small molecules as interface modifiers in TiO₂/P3HT hybrid solar cells. Our results show that small differences in the chemical structure of these molecules, for example, the presence of the -CH₂– group in the 2-thiopheneacetic acid (TAA), can greatly increase the TiO₂ surface wettability, improving the TiO₂/polymer contact. This effect is important to enhance exciton splitting and charge separation.