Secondary Spacer-Assisted Incorporation of π-Conjugated Bulky Divalent Ligands in Layered Perovskites

Incorporating low band gap bulky π-conjugated organic spacers into layered 2D lead halide perovskites can enable tunable, high-performance optoelectronic materials but has been limited to a few examples due to challenges integrating bulky cations into the layered structure. Here we present a general strategy employing a secondary small organic spacer to assist formation of layered perovskites containing bulky cations. Using naphthalene diimide hexyldiammonium (NDI-dH2+) as a model, we show that an assisting spacer, phenylethylammonium, even at >100 mol % loading, surprisingly does not primarily form its own perovskite phase but instead significantly improves crystallinity of (NDI-dH)PbI4 and charge transport. Carrier transport increases up to an order of magnitude, with out-of-plane mobility reaching 8.6 × 10–3 cm2 V–1 s–1. This approach also enables incorporation of divalent 5-bromoisoindigo hexyldiammonium (5BrISO-dH2+), which otherwise degrades during iodide formation, suggesting a valuable route for integrating novel bulky π-conjugated spacers into perovskites for next-generation tunable optoelectronics.