Ambipolar Electrochemical Doping of CsPbBr 3 Nanocrystals

Electronic doping underpins many semiconductor applications but has remained elusive for lead halide perovskite nanocrystals because their high density and low formation energy of defects easily compensate introduced dopants. Here, we use electrochemical doping as a strategy to avoid doping compensation. Electrochemical injection of electrons or holes into the nanocrystal is compensated by surface-adsorbed electrolyte counterions, therefore not compromising crystal structure. We accomplished ambipolar (n- and p-type) doped CsPbBr3 nanocrystals with charge carrier concentrations ranging from intrinsic up to 4.8 × 1017 cm–3 (corresponding to 0.25 charges per nanocrystal). We show that electrochemical doping is reversible and stable at these free carrier concentrations. The extent of doping and stability are enabled by the use of lecithin, a zwitterionic ligand that strongly binds to the surface of the CsPbBr3 nanocrystals while still allowing ion and electron transfer. Lecithin stabilizes the surface atoms by shifting the potentials for Pb2+ reduction and Br– oxidation outside of the bandgap. The inferred surface-chemistry design rules for stable electrochemical doping can also serve as a guideline for developing CsPbBr3 nanocrystals stable under high free-carrier concentrations in optoelectronic devices, such as light-emitting diodes or electronically triggered quantum light sources.