From Molecular Spacers to Conjugated Polymers in 2D Perovskites

ConspectusTwo-dimensional (2D) organic-inorganic hybrid perovskites provide a stable alternative to three-dimensional (3D) absorbers, which often suffer from sensitivity to moisture and light. However, the traditional 2D perovskite architecture functions as a "quantum-well" structure, where insulating organic cations form dielectric barriers that restrict both light absorption and charge transport. The research described in this account focuses on transforming these passive organic spacers into active electronic components. Specifically, this transformation is achieved by incorporating diynes (molecules with two adjacent triple bonds) directly into the perovskite lattice and inducing topochemical polymerization through thermal treatment, which results in the formation of a 2D perovskite that intercalates a conductive polymer between its inorganic layers.The incorporation of such a polymer brings drastic changes in the properties of these materials. For example, it can significantly reduce their bandgap by up to 1.5 eV, thereby moving absorption well into the near-IR (NIR) range. Similarly, it can also improve the conductivity of the resulting material by up to 3 orders of magnitude while also enhancing their hydrophobicity and overall stability.In this Account, we describe the synthesis and characterization of these hybrid materials, highlighting how the inorganic lattice preorganizes diacetylene ligands to facilitate solid-state reactivity. Further, we discuss the impact of oxidative doping, showing that the incorporation of stable organic radicals in the polymers enhances electrical conductivity and the material's absorption. We further establish the versatility of this strategy by expanding the library of diynes and halides, confirming that this approach is a robust and reproducible method for modifying the optoelectronic properties of various 2D perovskite scaffolds.Beyond fundamental material design, we discuss the application of these systems in high-performance optoelectronic devices, specifically air-processed NIR photodetectors. For instance, devices utilizing one of these polymerized 2D-perovskites exhibit remarkable responsivities on par with state-of-the-art devices. Ultimately, this account argues that the integration of conjugated polymers represents a paradigm shift for 2D perovskites, successfully transforming the organic spacer from a passive dielectric barrier into an electronically active component, thereby opening the door to new and exciting properties and applications.