Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters

Yatao Zou,Eduardo Solano,Weihua Lin,Sai Bai,Sabina Abbrent,Kaibo Zheng,Xiangchun Li,Tõnu Pullerits ,Jun Li,Julian A Steele,Jiřı́ Brus ,Omar F Mohammed,Jun Yin,Weidong Xu,Libor Kobera,Ying Yang,Maarten B J Roeffaers,Lei Cai,Osman M Bakr,Ivan G Scheblykin,Chaoyang Kuang,Peng Teng ,Guanhaojie Zheng,Feng Gao

doi:10.1038/s41467-021-25092-7

Abstract

Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.

Highlights

Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects
The chelating additives (CAs) we use are 5-aminovaleric acid (5AVA) and 3,6,9,12-tetraoxatetradecane-1,14-diamine (NH2–PEG4–NH2), which consist of commonly used amino- and/or carboxyl- groups; their respective mono-functionalized counterparts are n-butylamine (BA) and propionic acid (PA) for the former, and 2-(2-methoxyethoxy)ethanamine (m-PEG2–NH2) for the latter (Fig. 1a)
All the perovskite films show nano-island morphological features, the addition of CA leads to smaller crystal sizes and denser surface coverage compared to the mono-functionalized additives (MFAs)-based counterparts (Supplementary Fig. 3)

Summary

Introduction

Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. 7 Key Laboratory for Organic Electronics and Information Displays, Institute of Introducing molecular additives into perovskite precursors has become one of the most effective and prevailing strategies to improve the performance of metal halide perovskite lightemitting diodes (PeLEDs), and recently has boosted the external quantum efficiency (EQE) to high values above ~20%1–7. The critical factors underlying passivation effectiveness have been well identified, including hardness/softness of functional moieties[16], steric hindrance determined by molecular configurations[17,18], as well as hydrogen bonding between passivating functional groups and organic cations[7,19] Despite these advances in understanding molecular passivation, a widely observed phenomenon yet to be rationalized by passivation alone is that almost all the effective additives for perovskite emitters are chelating molecules that contain more than one electron-rich functional moiety[6,7,20]. We provide a universal guideline for tuning the crystallization dynamics for high-performance PeLEDs by leveraging the chelate effect

Methods

Results

Conclusion