Perovskites for Nonlinear Optics

Abstract

Nonlinear optics has been an important field since the invention of the laser and has enabled many advanced technologies, such as telecommunications, quantum technologies and super-resolution imaging. Nonlinear optical effects rely on the characteristic nonlinear response of a material and it is important to identify materials with the right properties for the right applications. Hybrid inorganic-organic perovksites have seen huge successes in the developments of photovoltaic, light emission and detection in the last decade. Their strength as a material for nonlinear optics, particularly in the third-order regime, has been the subject of recent investigation. However, the origin of nonlinearity of these hybrid perovksites remains unclear. In this work, the influence of anion on the nonlinear response of methylammonium lead halides (MAPbX3) was investigated. It is shown that an anion with a larger size leads to a stronger nonlinear response for the same family of materials. Although hybrid perovskites show strong nonlinear responses, they typically contain lead (Pb), which is toxic and not environmental friendly. Also, these materials possess bandgaps in the visible region, which is excellent for solar applications but could be a disadvantage for nonlinear applications because of the high two-photon absorption. Therefore, it is interesting to investigate materials with strong nonlinear responses and wide bandgaps, while also being environmentally friendly. Metal-free perovskites appear to be excellent alternatives. While this family of materials was originally designed for the interest of ferroelectric applications, there have been works demonstrating their potential in nonlinear applications, for instance, second harmonic generation. In this work, the examination of perovskite for nonlinear optics is extended to include the metal-free material DABCO-NH3-X3 and MDABCO-NH3-X3. All of these metal-free perovskites possess bandgaps of about 5 eV, which is significantly higher than that of their hybrid counterparts. The MDABCO-NH3-X3 variants demonstrated a nonlinear optical response that was an order of magnitude greater than the DABCO-NH3-X3 materials. It is believed that the introduction of methyl-group induces distortion of the octahedral, which leads to a stronger nonlinear response. A typical way to exploit the third-order nonlinear response of materials is using waveguides, in which the response can be enhanced due to the length of the material. MAPbBr3 and MDABCO-NH3-I3 crystals have been grown inside capillaries, in an attempt to form the first generation of optical fibre-like perovskite waveguides. While the transmission losses were quite high at 10 dBcm−1, it is noted that this is commensurate with the first generation of semiconductor optical fibres and provides a strong platform for waveguiding perovskite nonlinear optics.