RESUMEN
We report a mechanistic study of the photoluminescence (PL) enhancement in CsPbBr3 perovskite nanocrystals (PNCs) induced by organic/inorganic hybrid ligand engineering. Compared to the as-synthesized oleic acid-oleylamine modified PNCs, the tributylphosphine oxide-CaBr2 modified PNCs can achieve a better passivation effect due to strong PâO-Pb coordination and Br-vacancy remedy, resulting in enhanced PL efficiency. We employ steady-state/time-resolved/temperature-dependent PL and fluence/polarization-dependent ultrafast transient absorption spectroscopy to obtain a mechanistic understanding of such an enhancement effect from both nonradiative and radiative perspectives. As for the dominating nonradiative recombination suppression, we quantitatively evaluate the contributions from channels of exciton dissociation and exciton trapping, which are connected to exciton binding energy and activation energy of exciton trapping to surface defect-induced trap states, respectively. We also look into the radiative recombination enhancement, which is likely due to the increase in electron-hole overlap of photogenerated excitons induced by slight Ca-doping. These mechanistic insights would be of guiding value for perovskite-based light-emitting applications.
RESUMEN
Lead halide perovskite nanocrystals (LHP NCs) are regarded as promising emitters for next-generation ultrahigh-definition displays due to their high color purity and wide color gamut. Recently, the external quantum efficiency (EQE) of LHP NC based light-emitting diodes (PNC LEDs) has been rapidly improved to a level required by practical applications. However, the poor operational stability of the device, caused by halide ion migration at the grain boundary of LHP NC thin films, remains a great challenge. Herein, we report a resurfacing strategy via pseudohalogen ions to mitigate detrimental halide ion migration, aiming to stabilize PNC LEDs. We employ a thiocyanate solution processed post-treatment method to efficiently resurface CsPbBr3 NCs and demonstrate that the thiocyanate ions can effectively inhibit bromide ion migration in LHP NC thin films. Owing to thiocyanate resurfacing, we fabricated LEDs with a high EQE of 17.3%, a maximum brightness of 48000 cd m-2, and an excellent operation half-life time.
RESUMEN
Semiconductor materials were adopted in their solid states for photovoltaic applications owing to their nonsolubility and/or breaking of the photogenerated carrier transfer pathway in solution. The liquid-state photovoltaic device fills in a gap between currently prevailing full-solid-state and solid-liquid-state solar cells; however, reports on the photovoltaic effect from realistic semiconductor solution are absent so far. Herein, we report a hybrid inorganic-organic ionic semiconductor [Ni(Phen)3][V14O34Cl]Cl (Phen = 1,10-phenanthroline) and observe its photovoltaic effect in ionic liquid solution. This photovoltaic effect arises as a result of charge transfer between the coordination cation and inorganic polyoxovanadate in solution under illumination and subsequent transfer to electrodes. The liquid-state photovoltaic device (cell configuration: carbon cloth||[Ni(Phen)3][V14O34Cl]Cl in ionic liquid||Al foam) yields an open-circuit voltage of ca. 1.199 V and a photocurrent density of 3.268 mA cm-2 upon illumination using an air mass of 1.5 (100 mW cm-2) at 80 °C with a fill factor of 42.48% and an efficiency of 1.665%. This novel type of hybrid ionic semiconductor possesses great structural tunability for an optimized photovoltaic performance.
