Amine-free multi-faceted CsPbBr3 nanocrystals for complete suppression of long-lived dark states

Abstract

Conventional amine-capped perovskite nanocrystals (A-PNCs) often show microscopic fluctuation (blinking) of photoluminescence (PL) between bright and near-background (dark) states. The transient dark phases spanning milliseconds (ms) to several seconds timescale typically owe to the non-radiative (NR) fate of charge carriers in crystal defect states, limiting the PNC's efficiency in optoelectronics. A PL study of a novel trioctylphosphine (TOP) capped rhombic cuboctahedron-shaped amine-free (AF) PNC is presented, demonstrating their fascinating nonblinking nature. While oleylamine-capped hexahedron A-PNCs as a reference system show long dark states, their population is completely suppressed in ≈90% of AF-PNCs with random large-amplitude PL fluctuations several times above the background. The PL trajectories of AF-PNCs primarily comprise constant power spectral densities (PSDs) which are unprecedented and deviate from power-law distribution as observed for A-PNCs and most of the other blinking nanocrystals. Such signature of PSDs and frame-by-frame intensity jump analysis indicate a fast (<<ms) timescale charge-carrier dynamics governing the PL emission of AF-PNCs, likely involving short-lived metastable states. Besides, long-term stability and suppressed dark phases in ≈70% AF-PNCs even 90 days after the synthesis is noteworthy. Altogether the study provides exceptional optical characteristics of photostable amine-free PNCs which would be attractive to exploit in commercial display applications.