2, Jiangsu University of Science and Technology, Zhenjiang, , China
We report novel two-dimensional lead halide perovskite structures templated by a unique conjugated aromatic dication, N,N-dimethylphenylene-p-diammonium (DPDA). The asymmetrically substituted primary and tertiary ammoniums in DPDA facilitates the formation of two-dimensional network (2DN) perovskite structures incorporating a conjugated dication between the MX42- (M = Sn, Pb,; X = Br, I) layers. These 2DN structures of (DPDA)PbI4 and (DPDA)PbBr4 were characterized by single crystal X-ray diffraction, showing uniquely low distortions in the Pb-X-Pb bond angle for 2D perovskites. The Pb-I-Pb bond angle is very close to ideal (180°) for a 2DN lead iodide perovskite which can be attributed to the rigid diammonium DPDA’s ability to insert into the PbX62- octahedral pockets. Optical characterization of (DPDA)PbI4 shows an excitonic absorption peak at 2.29 eV (541 nm), which is red-shifted compared to similar 2DN lead iodide structures. Temperature dependent photoluminescence of both compounds reveal both a self-trapped exciton and free exciton emission feature. The reduced exciton absorption energy and emission properties are attributed to the dication induced structural order of the inorganic PbX42- layers. The 2D tin perovskite analog (DPDA)SnI4 showed similar structural distortions and bonding. To test the difference the choice of cation makes in 2D perovskites, quasi-2D (Ruddelson-Popper) perovskite structures were formed in thin-film solar cells using this new DPDA dication.