2D OIHPs with PEA fluorinated at different positions and their device characterization: a crystal sketch of PEA based 2D OIHP, n = 4; b molecular structures of PEA and its fluorinated derivatives in this study; c current-density-voltage, J-V, curves, forward scan, under 1 sun condition, AM.1.5 G, with a solar simulator; d device performance tracking under constant illumination and at maximum power point

Chemically Tuned 2D Perovskites

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. Yet, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported.

Published in Nature Communications, researchers in the You Research Group, demonstrate that the selection of spacer cations, in essence selective fluorination of phenethylammonium, affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells, average n = 4. Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties.

This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.