Impact of Amine Additives on Perovskite Precursor Aging: A Case Study of Light-Emitting Diodes

Abstract

Amines are widely employed as additives for improving the performance of metal halide perovskite optoelectronic devices. However, amines are well-known for their high chemical reactivity, the impact of which has yet to receive enough attention from the perovskite light-emitting diode community. Here, by investigating an unusual positive aging effect of CH 3 NH 3 I/CsI/PbI 2 precursor solutions as an example, we reveal that amines gradually undergo N-formylation in perovskite precursors over time. This reaction is initialized by hydrolysis of dimethylformamide in the acidic chemical environment. Further investigations suggest that the reaction products collectively impact perovskite crystallization and eventually lead to significantly enhanced external quantum efficiency values, increasing from ∼2% for fresh solutions to ≳12% for aged ones. While this case study provides a positive aging effect, a negative aging effect is possible in other perovksite systems. Our findings pave the way for more reliable and reproducible device fabrication and call for further attention to underlying chemical reactions within the perovskite inks once amine additives are included.

Deep‐Red Perovskite Light‐Emitting Diodes Based on One‐Step‐Formed γ‐CsPbI3 Cuboid Crystallites

“…[36] This result confirms the formation of blackphase CsPbI 3 perovskite with the help of FAI additive, which is consistent with previous reports. [33,37,38] Scanning electron microscopy (SEM) images show that PDAI additive will change the morphology from small grains with size of ≈50 nm to rectangular-shape crystals with sizes ranging from 50 to 350 nm (Figure 1b-d). SEM images also show that PDAI-CsPbI 3 film has lower film coverage than the control film.…”

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

“…Diamines have previously been incorporated into metal halide perovskites as additives in the precursor solution. − In particular, the addition of ethylenediamine (EDA) and ethylene diammonium iodide (EDAI 2 ) has been shown to lead to the formation of “hollow” materials in certain ABI 3 (A = MA + , FA + ; B = Pb 2+ , Sn 2+ ) perovskites, whereby diammonium dications are incorporated into the perovskite structure, along with B 2+ and X – vacancies, to enable steric accommodation of the EDA dications and balancing of the overall charge, respectively. , In addition, the use of EDA via post-treatment of the surface has been reported to afford increased efficiency and stability in Pb–Sn perovskites . Likewise, dimethylammonium is another bulky cation, which is too large to incorporate into many halide perovskite compositions according to the Goldschmidt tolerance factor considerations but in some cases has been shown to increase both the bandgap, open-circuit voltage ( V OC ) and overall performance of perovskite solar cells, despite negatively impacting the compositional heterogeneity of those films. − Motivated by these observations, we hypothesized that the addition of EDA might be beneficial for formulations close to the 1.7 eV bandgap ideal for silicon-perovskite tandems.…”

Stirring-Time Control Approach to Manage Colloid Nucleation Size for the Fabrication of High-Performance Sn-Based Perovskite Solar Cells

“…In addition, the long-term existence of amine materials like FAI in the perovskite precursor solution will cause an N-formylation reaction, which also affects the quality of the resulting perovskite film. 39 Therefore, the Snbased perovskite precursor solution should not be left for too long. Furthermore, we detect the presence of SnI 2 in the newly dissolved film (12.8°, Figure 5a), 40 corresponding to the white dots in the SEM image (Figure 3a).…”

“…Combining with the previous related research, we believe that this is closely related to part oxidation of Sn 2+ to Sn 4+ during the long-term stirring process due to the use of DMSO in the FA 0.75 MA 0.25 SnI 3 precursor solution. , The presence of Sn 4+ affects the crystallization of FA 0.75 MA 0.25 SnI 3 perovskite and also causes more defects in the film. In addition, the long-term existence of amine materials like FAI in the perovskite precursor solution will cause an N -formylation reaction, which also affects the quality of the resulting perovskite film . Therefore, the Sn-based perovskite precursor solution should not be left for too long.…”