High efficiencies of over 20% have been reported in the literature for both planar and mesoscopic hybrid perovskite solar cells, and the preferred configuration for scale-up and commercialization is still a matter of debate. The mesoscopic configuration generally requires a high-temperature processing step, which limits applications and makes the process less cost-effective. We have used low-temperature (LT) processing (≤120 °C) to fabricate high-efficiency planar and mesoscopic TiO₂-based hybrid perovskite solar cells with comparable performance, highlighted by a champion LT mesoscopic solar cell with 16.2% efficiency. Photovoltaic efficiencies of 14–16% have been achieved for a mesoporous film thickness ranging from 120 to 480 nm by fine-tuning the precursor solution chemistry. The presence of the LT mesoporous layer improves the preservation of performance under conditions of relative humidity of 60%, especially under illumination. Impedance spectroscopy illustrates a similarity of the locus and kinetics of the recombination processes for both configurations. However, inductive loops usually related to ion migration are observed showing different characteristics between both configurations, pointing to the previously suggested correlation between ion migration and degradation. These results suggest that the beneficial role of a mesoporous TiO₂ layer might be the stabilization of harmful defects at the perovskite/electron extraction layer interface, and indicate that interface engineering is critical to achieving improved long-term performance.