We report annealing-free compact TiO_x layer by atomic layer deposition for high efficiency flexible perovskite solar cells, and maintained 95% of the initial PCE after 1000 bending cycles with 10 mm bending radius.

MgO-coated TiO₂ nanoparticle (NP)-based electron collecting layers were fabricated to prevent charge recombination at the methylamine lead iodide/TiO₂ interface in perovskite solar cells. The open circuit voltage (V_oc) and fill factor (ff) of perovskite solar cells based on MgO-coated TiO₂ charge collectors were 0.89 V and 71.2%, respectively. These values were 4.7% and 6.1% higher than the pure TiO₂ based perovskite solar cells. Transient photovoltage decay data exhibited recombination times for MgO-coated TiO₂ NP-based perovskite solar cells about three times longer than those of TiO₂ NP based solar cells. The longer recombination time was responsible for enhancing the V_oc and ff of MgO-coated TiO₂ NP-based perovskite solar cells. By employing a MgO nanolayer, we observed that the power conversion efficiency (PCE) was increased from 11.4% to 12.7%, demonstrating that MgO ultrathin nanolayers are able to efficiently retard charge recombination in perovskite solar cells.