Naphthalenediimide Cations Inhibit 2D Perovskite Formation and Facilitate Subpicosecond Electron Transfer

Layered metal halide perovskites, also called perovskite quantum wells (PQWs), are versatile optoelectronic materials possessing large oscillator strengths, band gaps tuned via the quantum size effect, and promising stability. The majority of examples of PQWs make use of small aryl- and alkylammonium A'-site cations to tune dimensionality and stability, with fewer examples of larger molecules that exhibit frontier orbital energies near those of the inorganic component of the perovskite. Here, we report two new lead-iodide-based systems that incorporate a dye molecule A'-site dication, 2,2'-[naphthalene-1,8:4,5-bis(dicarboximide)-N,N'-diyl]-bis(diethylammonium) (NDIC2), along with either methylammonium or a mixture of methylammonium and formamidinium as A-site cations. From transient absorption spectra, we find that films synthesized with NDIC2, PbI2, and methylammonium inhibit the growth of PQWs and instead result in a mixture of weakly confined perovskite and 1D perovskitoid structures. When both formamidinium and methylammonium are used as A-site cations, we observe spectroscopic signatures of quantum-confined 2D structures similar to PQWs with a polydisperse well width distribution. We observe a rapid (similar to 700 fs) decay of the photoexcited perovskite carrier population in the presence of NDIC2 and fully quenched photoluminescence: this is consistent with ultrafast perovskite-to-NDIC2 electron transfer. This work explores the interplay between large and small cation molecules in influencing the perovskite structure and how such molecules may offer a route to structures with charges separately localized on inorganic and organic components, raising prospects of using perovskites with electron-accepting ligands for hybrid organic-inorganic optoelectronic devices.