Boosting Tunable Blue Luminescence of Halide Perovskite Nanoplatelets through Postsynthetic Surface Trap Repair

Abstract

The easily tunable emission of halide perovskite nanocrystals throughout the visible spectrum makes them an extremely promising material for light-emitting applications. Whereas high quantum yields and long-term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields, broad emission profiles, and insufficient colloidal stability. In this work, we present a facile synthetic approach for obtaining two-dimensional CsPbBr nanoplatelets with monolayer-precise control over their thickness, resulting in sharp photoluminescence and electroluminescence peaks with a tunable emission wavelength between 432 and 497 nm due to quantum confinement. Subsequent addition of a PbBr-ligand solution repairs surface defects likely stemming from bromide and lead vacancies in a subensemble of weakly emissive nanoplatelets. The overall photoluminescence quantum yield of the blue-emissive colloidal dispersions is consequently enhanced up to a value of 73 ± 2%. Transient optical spectroscopy measurements focusing on the excitonic resonances further confirm the proposed repair process. Additionally, the high stability of these nanoplatelets in films and to prolonged ultraviolet light exposure is shown.

Recent advances and prospects toward blue perovskite materials and light‐emitting diodes

“…Moreover, both pristine and treated NCs exhibit a narrow PL emission with a FWHM of 11 nm, confirming the high uniformity of the NCs. The doping and passivation of the above metal ions can break the restriction of efficiency caused by deep level defects reported by other publications …”

“…Moreover, changes in the molar amount of Cs cation can control the thickness of NPL. This is because the thickness of 2D perovskites is determined by the equilibrium of the surfactants and precursors across two phases . The amount of the A‐site cations decreases with respect to the other precursors, limiting the formation of perovskites.…”

“…A, Colloidal CsPbBr 3 NPL dispersion was obtained by control of Cs/Pb ratios. Reproduced with permission from Reference . Copyright 2018, American Chemical Society.…”

“…Wu et al passivated surface defects of NPLs by PbBr 2 to obtain a PLQY of approximately 100%, making the all‐inorganic perovskite NPLs an attractive candidate for pure blue LEDs . Bohn et al passivated NPL surface defects (Figure A) in a similar way to obtain highly efficient all‐inorganic perovskite NPLs and subsequently constructed blue LEDs based on three monolayer (3ML) NPLs . As shown in Figure B, the device presented a pure blue emission with a single narrow EL peak (FWHM <20 nm).…”

Unveiling the Photo‐ and Thermal‐Stability of Cesium Lead Halide Perovskite Nanocrystals

“…CsPbX 3 nanocrystals have been incorporated into solar cells achieving a record 13.4 % power conversion efficiency (PCE). [15] Other syntheses have expanded this general idea by generating multiple nanocrystal morphologies through ligand mediation [21][22] and reaction tuning, [23] by using different surface ligands for improved quantum yields, [24][25] by increasing surface passivation/repair via salt solutions, [26][27][28][29] as well as by generating other cation/anion compositions through doping [17,[30][31][32][33][34][35] or post-synthetic ion exchange. [12,[19][20] Most reported syntheses of CsPbX 3 follow the work of Protesescu et al who demonstrated a simple, solution-based synthesis for nanocrystals with high luminescence.…”