Two-Dimensional Hybrid Dion–Jacobson Germanium Halide Perovskites

Chen C., Zhao Z., Gong Y., Liu Y., Chen Z., Zhang L., Chen J., Deng Z., Lu H., Luo M., Canepa P., and Mao L.; Chem. Mater. (2023).


Hybrid two-dimensional (2D) halide perovskites have emerged as an important class of high-performance semiconductors because of their excellent physical properties and structural diversity. Here, we report a new family of hybrid 2D Ge-based perovskites that have the Dion–Jacobson structure type, with the general formula A(MA)n–1GenX3n+1, where A = 2-(aminomethyl)pyridinium (2AMPY), 3-(aminomethyl)pyridinium (3AMPY), 4-(aminomethyl)pyridinium (4AMPY), or 4-(aminomethyl)piperidinium (4AMP), X = Br or I, and n = 1 or 2. Single-crystal X-ray diffraction shows that most of the bromide structures are centrosymmetric, whereas the iodide analogues are all non-centrosymmetric. The optical band gaps are effectively regulated by the level of octahedral distortion of the corresponding [GeX6], where a larger distortion corresponds to a larger band gap. These compounds exhibit relatively weak photoluminescence, which can be observed at low temperatures. All of the Ge-based iodide perovskites exhibit good second-harmonic generation (SHG) responses, with the highest reaching 0.53xAgGaS2 for (4AMPY)GeI4, where their particle-dependent SHG has been investigated. First-principles calculations of the SHG properties are in good agreement with the experimental results. Furthermore, layer transformation can be achieved from the (100)- to (110)-oriented configuration by mixing the halides, which is a rare example. These results showcase the versatility and diversity of employing an asymmetric dication and the Ge2+ metal to achieve SHG active non-centrosymmetric materials, providing new strategies for the design of lead-free alternatives with interesting photophysical properties.