Efficient Light-Emitting Diodes Based on in Situ Fabricated FAPbBr₃ Nanocrystals: The Enhancing Role of the Ligand-Assisted Reprecipitation Process

Abstract

In this paper, we reported the in situ fabrication of highly luminescent formamidinium lead bromide (FAPbBr) nanocrystal thin films by dropping toluene as an anti-solvent during the spin-coating with a perovskite precursor solution using 3,3-diphenylpropylamine bromide (DPPA-Br) as a ligand. The resulting films are uniform and composed of 5-20 nm FAPbBr perovskite nanocrystals. By monitoring the solvent mixing of anti-solvent and precursor solution on the substrates, we illustrated the difference between the ligand-assisted reprecipitation (LARP) process and the nanocrystal-pinning (NCP) process. This understanding provides a guideline for film optimization, and the optimized films obtained through the in situ LARP process exhibit strong photoluminescence emission at 528 nm, with quantum yields up to 78% and an average photoluminescence lifetime of 12.7 ns. In addition, an exciton binding energy of 57.5 meV was derived from the temperature-dependent photoluminescence measurement. More importantly, we achieved highly efficient pure green perovskite based light-emitting diode (PeLEDs) devices with an average external quantum efficiency (EQE) of 7.3% (maximum EQE is 16.3%) and an average current efficiency (CE) of 29.5 cd A (maximum CE is 66.3 cd A) by adapting a conventional device structure of ITO/PEDOT:PSS/TFB/perovskite film/TPBi/LiF/Al. It is expected that the in situ LARP process provides an effective methodology for the improvement of the performance of PeLEDs.

Trivalent‐Neodymium Additive Modulated MAPbBr3 Perovskite Nucleation and Growth: Ultrawide Processing Window for One‐Step Fabrication of Efficient Light‐Emitting Perovskites

“…To determine the length of the processing time window, we used the combination of a high PLQY and a uniformly covered smooth surface as the defining criteria, in accordance with previous reports 7,16. Furthermore, we proposed a set of quantitative criteria (film coverage >90% and grain size <5 µm) to determine the boundaries of processing window more precisely, and the details are described in the Supporting Information.…”

“…R4 or S4 and R5 or S5 are samples treated with the antisolvent 2 s and 6 s after the optimal time, respectively. For the pristine thin films, samples fabricated with earlier dripping times (R1 and R2) exhibit obvious ring effects, while the delayed dripping time (R4 and R5) leads to rough, dimmed thin films 7. In contrast, the MAPbBr 3 :Nd(5%) thin films (S1–S5) remain mirror‐like and macroscopically flat even over a greatly broadened processing window larger than 18 s.…”

“…Thus, optimizing the processing techniques to overcome this challenge is highly desirable. Han et al reported highly luminescent LEDs based on formamidinium lead bromide (FAPbBr 3 ) nanocrystals obtained by ligand‐assisted reprecipitation, and the processing window was broadened to 4 s. However, for industrial production, the processing window still needs to be substantially improved 7…”

Metal halide perovskite nanocrystals and their applications in optoelectronic devices

“…In the process of spin coating of a perovskite precursor solution with 3,3‐diphenylpropylamine bromide as a ligand, FAPbBr 3 NC film was prepared in situ by adding toluene as an antisolvent. Using ITO/PEDOT: PSS/poly(9,9‐dioctyl‐fluorene‐co‐N‐[4‐butylphenyl]diphenylamine) (TFB)/perovskite film/TPBi/LiF/Al conventional device structure, green LEDs with EQE of 16.3% were obtained (Figure ) …”

“…Reproduced with permission. Copyright 2018 American Chemical Society . EL, electroluminescence; EQE, external quantum efficiency; LEDs, light‐emitting diodes; NC, nanocrystal…”