As a promising non-toxic alternative to lead-halide perovskites, Cs2AgInCl6 double perovskite (DP) nanocrystals (NCs) exhibit a charge neutral, 3-dimensional (3D) structure with excellent stability and novel optoelectronic properties. Despite this, the low photoluminescence quantum yield (PLQY) that arises from a low absorption coefficient and parity forbidden transitions limit their use in applications. Transition metal cation doping is a common strategy implemented to improve PLQY, however, direct synthetic means offers little insight into NC-dopant interaction. Here, we report a Na/Mn co-doped Cs2AgInCl6 DP with a PLQY of 8.2% that was achieved via a liquid/solid post-synthetic doping mechanism. As such, amine-based ligands were utilized in a ligand-activation complexation to achieve Mn2+ dispersion in nonpolar solvent, while an organometallic Na+ precursor was synthesized. First, time resolved dopant-DP diffusion dynamics were interpolated through optical spectroscopies, electron paramagnetic resonance (EPR) and X-ray diffraction (XRD) to not only determine dopant-NC interactions but also dopant-dopant interactions. Furthermore, an in-depth study was conducted for precise post-synthetic ligand engineering. Namely, introduction of the slightly acidic Na+ precursor induced amine protonation to produce an ammonium compound. Proton Nuclear Magnetic Resonance (H-NMR) analysis indicates ligand exchange, while nuclear Overhauser effect spectroscopy (NOESY) showed favorable ammonium binding, and diffusion ordered spectroscopy (DOSY) was used to determine binding affinity. Ultimately, this study exemplifies the simultaneous co-doping and particle stabilization that arises from acid/base reactions in a liquid/solid post-synthetic method.

Post-synthetic Na/Mn codoping and ligand engineering of Cs2AgInCl6 double perovsite nanocrystals

ACS Spring 2022

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