Transformation of Quasi‐2D Perovskite into 3D Perovskite Using Formamidine Acetate Additive for Efficient Blue Light‐Emitting Diodes

Abstract

Perovskite films have emerged as candidates for light‐emitting diodes on accounts of excellent optical properties and low cost. Construction of quasi‐2D perovskite films by incorporating organic ammonium is an effective method to manufacture a pinhole‐free film with high photoluminescence quantum yield (PLQY). However, excess organic ammonium hampers carrier mobility through forming insulating capping layer and facilitates the formation of alow‐dimensional perovskite (n = 1 and n = 2) phase that accelerates non‐radiative recombination, resulting in poor performance of light‐emitting diodes. In this work, formamidine acetate is added into the quasi‐2D perovskite to modulate the optical and electrical properties of the perovskite films (CsFA‐Ac). Acetate ions are in favor of washing away excess ammonium and formamidine ions are beneficial to increase the formation energy of low‐dimensional (n = 2) phase. As a result, the quasi‐2D perovskite is transformed into 3D perovskite. The PLQY of the obtained CsFA‐Ac perovskite films is boosted to 59.9% and carrier mobility is enhanced to 47.3 cm2 V‐1 s‐1. Blue perovskite light‐emitting diode based on the CsFA‐Ac film is endowed with a prominent EQE of 8.8% (average 7.0%) at 477 nm. This work demonstrates a strategy for the development of efficient perovskite light‐emitting diodes.

Rearranging the Phase Distribution of Quasi-2D Perovskite for Efficient and Narrow Emission Perovskite Light-Emitting Diodes

“…We further examined the passivation of l -TrpBr in the performances of quasi-2D PeLEDs. Figure c shows that the turn-on voltage ( V on ) is reduced from 2.8 to 2.6 V, and the maximum luminance increased from 11 827 to 37 785 cd m –2 after introducing l -TrpBr, confirming that the defects in quasi-2D perovskite films were suppressed by l -TrpBr . Furthermore, the peak EQE of the champion device reaches 14.32% at 1526 cd m –2 at a current density of 3.17 mA cm –2 (Figure d).…”

A Demulsification–Crystallization Model for High‐Quality Perovskite Nanocrystals

“…Preparation of the Precursors: Cs 2 CO 3 , FA(Ac), and Na 2 CO 3 were dissolved in OTAc with the molar concentration of 0.1, 0. , and 0.1 m as Cs-solution, Ac-solution (FA + cation is selected as the cation regarding the stability of the lattice [38] ), and OTAc-solution, respectively. During the dissolution process, the CO 3 2− will become CO 2 and generate octoate.…”

Reduced Confinement Effect by Isocyanate Passivation for Efficient Sky‐Blue Perovskite Light‐Emitting Diodes

“…[35] Based on this research conclusion, it has also been reported that a low exciton binding energy, which represents the weak quantum confinement effect, is beneficial to improving the photoelectric properties of 2D perovskites. [36,37] According to the fitting results of temperature-dependent PL measurements above, the smaller E b value of the target perovskite film indicated the reduced confinement effect, which was more conducive to carrier injection and transfer. To further test our conjecture, hole-only (Figure 3e) and electron-only (Figure 3f) devices with the structure of ITO/PVK/perovskite/MoO 3 /Ag and ITO/SnO 2 /perovskite/PO-T2T/Liq/Al respectively were constructed.…”