Anomalous inclusion of chloride ions in ethylenediammonium lead iodide turns 1D non-perovskite into a 2D perovskite structure

In this work, we demonstrate that 1D EDPbI4 crystals containing face-sharing PbI64- octahedra are synthesized using ethylenediammonium (ED) as an organic cation in hydroiodic acid. However, by the addition of hydrochloric acid to the synthetic solution, 2D [(ED)2PbI4]Cl2 crystals are interestingly constructed without substitution of iodides by chlorides. The importance of chloride ions in the structure has been revealed by employing the single-crystal X-ray diffraction technique. Isolated chlorides, through forming hydrogen bonds with ammonium groups and creating (ED)2Cl22+ templating layers, lessen the interplays between organic cations and inorganic units and consequently lead to the formation of almost undistorted PbI42- perovskite layers. The band gaps of the resultant crystals have been determined to be 2.72 eV and 2.30 eV for EDPbI4 and [(ED)2PbI4]Cl2, respectively. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements indicate that both compounds are thermally stable up to 250 °C without any phase transition.