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Carbide polymer dots enable efficient large-area perovskite light-emitting diodes


1. Guide

Metal halide perovskites stand out among many optoelectronic materials due to their ease of solution processing, low manufacturing cost and excellent photoelectric properties, and are strong candidates for the next generation of commercial light-emitting diode light-emitting layers. High-quality perovskite layers are a prerequisite for achieving high-efficiency perovskite light-emitting diodes (PeLEDs).

Recently, the team of Professor Yang Bai of the State Key Laboratory of Supramolecular Structure and Materials of the School of Chemistry of Jilin University and the team of Professor Zhang Xiaoyu of the School of Materials Science and Engineering of Jilin University proposed a method to regulate the growth interface of quasi-two-dimensional perovskite crystals through carbonized polymer points, which effectively improved the uniformity of perovskite films by improving the ion adsorption type at the quasi-two-dimensional perovskite growth interface, and realized large-area PeLEDs devices with an external quantum efficiency of 20.2%.

2. Research background

In the perovskite family, quasi-two-dimensional perovskites have a unique natural quantum well structure, high exciton binding energy, and the ability to adjust the band gap to cover the entire visible region through dimensional and component control, which is in line with BT. A promising luminescent material for the 2020 standard.

However, despite the recent rapid improvement in the efficiency of quasi-2D PeLEDs, researchers mainly focus on small-area devices, and there is still a certain gap between the actual large-area display. The existing strategies to improve the uniformity of large-area films mainly focus on suppressing the “coffee ring effect”. In fact, the formation of perovskite polycrystalline films involves not only solute deposition but also complex subsequent crystal nucleation and growth, so determining the determinants of achieving homogeneous films remains challenging.

In the formal devices of quasi-two-dimensional PeLEDs, the solid-liquid interface between the hole transport layer and the perovskite precursor is considered to be a crucial existence, which is not only a fortress for hole injection into the light-emitting layer, but also affects the quality of quasi-two-dimensional perovskite crystal growth as a crystal growth substrate. By introducing a defect passivator at this interface, researchers can effectively reduce the non-radiative recombination of charge at the interface and reduce energy loss, which is an effective method to improve the efficiency of perovskite devices. In fact, this interface not only affects the longitudinal growth and charge transport of perovskite crystals, but also has an important impact on the uniformity of the entire polycrystalline film, so the specific influence mechanism of the crystal growth interface on perovskite films needs to be further revealed.

3. Innovative research

3.1 Functional Materials

Fig. 1 Carbonized polymer point synthesis and protonation.

The authors synthesized amino-rich carbide polymer dots on the surface by hydrothermal method and introduced them into the acidic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) hole transport material, thereby regulating the surface properties of the hole transport layer. The carbonized polymer fractions are protonated by binding to hydrogen ions in an acidic environment while inhibiting phase separation during membrane formation in the hole transport layer (Figure 1).

Fig. 2 Effect of carbonized polymer point alignment with 2D perovskite film uniformity.

The carbonized polymer point effectively improves the uniformity of the perovskite film without changing the wettability of the perovskite precursor solution on the growth substrate (Figure 2).

3.2 Film homogenization mechanism

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Fig. 3 The carbonized polymer dots changed the type of substrate-to-ion tendency.

The authors conducted a series of experiments to explore the mechanism by which carbonized polymer point alignment improves the uniformity of quasi-2D perovskite films (Figure 3). The amino groups protonated on the surface of the carbonized polymer point tend to interact with anions or anion groups in the perovskite, and the grain growth substrate adsorbs specific ions through interaction, causing changes in the concentration of interfacial ions. In the absence of CPDs, the original substrate has a strong interaction with metal cations, resulting in a sharp decrease in cation concentration at the interface. Under the regulation of CPDs, the interaction turns to anionic and anionic groups, which exhibit slight interference due to the higher concentration of anionic and anionic groups.

3.3 Device performance improvement

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Fig.4. Properties characterization of perovskite films.

Differences in the interaction between the grain growth substrate and the precursor solution result in changes in crystal orientation and defects (Figure 4). Due to the strong interaction between the protosubstrate and the metal ions, the nucleation distribution and subsequent crystallization are disrupted, resulting in a more random crystal orientation. The interface of carbon polymer point regulation changes the nucleation type and reconstructs the thin film structure by enhancing the interaction with anions and weakening the interaction with cations. Unsaturated metal ions and halogen vacancies may become defect centers, and the optimization of carbonized polymer points effectively reduces defects.

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Figure 5 LED device performance.

Based on the improvement of the uniformity of perovskite films, the orientation of crystal growth and the inhibition of defects by carbonized polymer dots, the authors prepared light-emitting diode devices (Figure 5). The efficiency of the small-area device increased from 19.4% to 24.4%, and further carrier transport balance optimization increased the efficiency of the device to 24.6%, based on the uniform perovskite emitting layer, the authors successfully prepared a large-area quasi-two-dimensional light-emitting diode with a luminous area of 225 mm2 and an efficiency of 20.2%.

4. Application and prospects

In this work, the influencing mechanism affecting the growth uniformity of quasi-two-dimensional perovskite films is discussed, and the dominant interface properties of anions and anionic groups are adjusted by functionalized carbonized polymer points, which significantly improves the morphology and quality of the films, improves the device efficiency of small-area light-emitting diodes, promotes the uniform luminescence of large-area devices, and promotes the practicability of perovskite light-emitting diodes.

The research results were published online in Light: Science & under the title “Rational adjustment to interfacial interaction with carbonized polymer dots enabling efficient large-area perovskite light-emitting diodes” Applications。

The first author of this paper is Yang Fan, a doctoral student at the State Key Laboratory of Supramolecular Structures and Materials, College of Chemistry, Jilin University, and co-corresponding authors, Professor Yang Bai, State Key Laboratory of Supramolecular Structures and Materials, College of Chemistry, Jilin University, and Professor Zhang Xiaoyu, School of Materials Science and Engineering, Jilin University. (Source: LightScience Applications WeChat public account)

Related paper information:https://www.nature.com/articles/s41377‍-023-0‍1150-71

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