In Situ 2D Perovskite Formation and the Impact of the 2D/3D Structures on Performance and Stability of Perovskite Solar Cells

Hybrid organic and inorganic perovskite solar cells lack long‐term stability, and this negatively impacts the widespread application of this emerging and promising photovoltaic technology. Herein, aiming to increase the stability of perovskite films based on CH 3 NH 3 PbI 3 and to deeply understand the formation of 2D structures, solutions of alkylammonium chlorides containing 8, 10, and 12 carbons are introduced during the spin‐coating on the surface of 3D perovskite films leading to the in situ formation of 2D structures. It is possible to identify the chemical formulae of some 2D structures formed by X‐ray diffraction and UV–vis analysis of the modified films. Interestingly, the increase in the stability of the CH 3 NH 3 PbI 3 films due to the formation of a 2D + 3D perovskite network is only possible in planar TiO 2 substrates. The increase in stability of the CH 3 NH 3 PbI 3 films follows the surfactant molecule order: octylammonium (8C) > decylammonium (1 °C) > dodecylammonium (12C) chlorides > standard. An increase of 17.6% in the lifetime of the devices assembled with octylammonium‐modified perovskite film is observed compared with that of the standard device, which is directly linked to the improvement of the charge carrier lifetimes obtained from time‐correlated single photon counting measurements.