Linear Electro‐Optic Modulation in Highly Polarizable Organic Perovskites

Electrical‐to‐optical signal conversion is widely employed in information technology and is implemented using on‐chip optical modulators. State‐of‐the‐art modulator technologies are incompatible with silicon manufacturing techniques: inorganic nonlinear crystals such as LiNbO3 are integrated with silicon photonic chips only using complex approaches, and hybrid silicon–LiNbO3 optical modulators show either low bandwidth or high operating voltage. Organic perovskites are solution‐processed materials readily integrated with silicon photonics; and organic molecules embedded within the perovskite scaffold allow in principle for high polarizability. However, it is found that the large molecules required for high polarizability also require an increase of the size of the perovskite cavity: specifically, using the highly polarizable DR2+ (R = H, F, Cl) in the A site necessitates the exploration of new X‐site options. Only by introducing BF4– as the X‐site molecule is it possible to synthesize (DCl)(NH4)(BF4)3, a material exhibiting a linear EO coefficient of 20 pm V–1, which is 10 times higher than that of metal halide perovskites and is a 1.5 fold enhancement compared to reported organic perovskites. The EO response of the organic perovskite approaches that of LiNbO3 (reff ≈ 30 pm V–1) and highlights the promise of rationally designed organic perovskites for use in efficient EO modulators. The linear electro‐optic (EO) effect in organic perovskites is demonstrated. The crystal structures and polarizability can be modified by the rational design of the organic components to realize an enhancement of the EO performance. This work provides a molecular perspective on the design of organic perovskites for EO modulation and new applications in nonlinear optics.