Tetrazine-incorporating layered halide perovskites featuring type II electronic interface: a small cation with several optical and electronic resonances

Layered halide perovskites are a class of semiconductors easily produced via chemical approaches and showing unique optical and electronic properties. These materials have a natural quantum-well electronic structure, that is, the band-gap of the inorganic frame is embedded into that of the organic spacers,[1] and feature effective light absorption, positive in-plane transport properties, effective narrow linewidth emission and improved stability against their 3D counterpart.[2] On the other hand, confinement of semiconducting properties in an inorganic is not ideal for applications where photogenerated species are required to effectively travel within the optically active component. This is the typical case of photovoltaics, where ineffective out-of-plane charge transport results in depleted performances for layered halide perovskites, as compared to 3D analogues.[3] In this frame, substituting the (usually) electronic inert organic spacer with organic chromophores featuring extended -conjugated core can pave the way for layered materials showing improved charge and energy transport properties.[4] Indeed, the band-gap closing due to extended -electronic conjugation can result in the (de)stabilization of the frontier orbitals of the spacer, compared to those of the inorganic frame, resulting in the formation of a type II heterojunction at the organic/inorganic interface. Here, we discuss the related charge/energy transfer processes on the basis of recently reported PbX4 (X=Cl,Br) layered perovskite frame incorporating tetrazine derivative as organic spacer.[5] Thanks to the various energy resonances between the inorganic and the organic component, both at the level of the single particle electronic states and at the level of many-body exciton states, this system represents the ideal test case to discuss in the detail charge and energy transfer processes at the type II interface. Furthermore, the incorporation of this novel chromophore as spacer is based on a new design concept, which exploits heterocycles with large fraction of nitrogen, rather than extending the size of carbon-based -core.[6] Photoluminescence (PL) and Photoluminescence Excitation (PLE) measurements indicate partial energy transfer from the inorganic frame to the organic component. Furthermore, cutting-edge, periodic DFT simulations suggest potential exciton ionization as potential responsible for the suppressed light emission from the perovskite frame. REFERENCES [1] C. Katan, et al. Chem. Rev. 2019, 119, 3140−3192 [2] M. D. Smith, et al., Chem. Rev. 2019, 119, 3104−3139 [3] H. Tsai, et al., Nature 2016, 536, 312–316 [4] D. B. Mitzi, et al., Inorg. Chem. 1999, 38, 6246-6256 [5] F. Ledée et al., revised manuscript submitted to Mater. Horiz. [6] Y. Gao, Nat. Chem. 2019, 11, 1151–1157