Unraveling the Formation Mechanism of the 2D/3D Perovskite Heterostructure for Perovskite Solar Cells Using Multi-Method Characterization

The formation of a two-dimensional (2D) three-dimensional (3D) perovskite heterostructure has lately proved to be a promising way to improve the interface between the perovskite and electron/hole transport layers in perovskite solar cells, which is crucial for better device efficiency and stability. Herein, a spacer cation, 4-fluorophenethylammonium iodide, in isopropyl alcohol was used to form a thin 2D perovskite layer on top of a 3D triple-cation perovskite by a spin-coating deposition process. Therefore, a significant improvement in the device open-circuit voltage is obtained, leading to an enhanced power conversion efficiency. The formation mechanism of the 2D perovskite layer was studied by analyzing the structural, chemical, and optoelectronic properties of the layer, while varying several synthesis parameters. We reveal the presence of bromide inside the 2D phase and conclude with the existence of a concomitant formation mechanism, besides the most commonly described one involving the lead iodide (PbI2) excess contained in the 3D bulk. Therefore, we demonstrate how the stoichiometry of the 2D perovskite is affected by the chemical composition of the 3D layer underneath. This work provides new insights into the synthesis mechanisms of 2D/3D perovskite heterostructures, which could help to optimize their fabrication processes and develop new efficient and functional 2D/3D structures.

Automated summary

The formation of 2D/3D perovskite heterostructures has shown promise in improving the interface between perovskite and electron/hole transport layers in solar cells. In this study, a thin 2D perovskite layer was formed on top of a 3D triple-cation perovskite using a spacer cation in isopropyl alcohol. This resulted in a significant improvement in device open-circuit voltage and power conversion efficiency. The study also revealed the presence of bromide in the 2D phase and demonstrated the impact of the chemical composition of the underlying 3D layer on the stoichiometry of the 2D perovskite.