Phase control of quasi-2D perovskite thin films by adding MAPbI₃ in the precursor solution

Quasi two-dimensional (Q-2D) perovskite cells have attracted much attention due to their excellent stability compared to their 3D counterparts. However, the Q-2D perovskite thin films prepared by the solution method have been confirmed to be a mixture of small-n phases and large-n phases instead of a pure phase, where the amount and distribution of these phases have a great significance on the performance of Q-2D perovskite solar cells. Here, commercialized 3D perovskite powder was simply added to an ACI perovskite precursor solution to get a uniform and closely connected heterostructure in which the large-n phases can work as pathways for charge transfer. The characterization results of the films and devices show that the appropriate amount of MAPbI₃ in the precursor solution could distribute the 3D phases homogeneously within the final film to promote the photovoltaic performance of the devices. Consequently, the power conversion efficiency of the Q-2D ACI perovskite solar cell has been increased from 10.4% to 13.82% (with a 32.8% performance improvement).