Intermediate-phase-assisted low-temperature formation of \u03b3-CsPbI3 films for high-efficiency deep-red light-emitting devices

Chang Yi,Ning Fan,Yong Yu,Fuxiang Ji,Xiao-Ke Liu,Chen Xue,Bo Ma,Kaichuan Wen,Hao Zhang,Jianpu Wang,Chaoyang Kuang,Ya Zhang,Chao Liu,Cailing Tu,Renzhi Li,Feng Gao,Wei Huang

doi:10.1038/s41467-020-18380-1

Abstract

Black phase CsPbI3 is attractive for optoelectronic devices, while usually it has a high formation energy and requires an annealing temperature of above 300 °C. The formation energy can be significantly reduced by adding HI in the precursor. However, the resulting films are not suitable for light-emitting applications due to the high trap densities and low photoluminescence quantum efficiencies, and the low temperature formation mechanism is not well understood yet. Here, we demonstrate a general approach for deposition of γ-CsPbI3 films at 100 °C with high photoluminescence quantum efficiencies by adding organic ammonium cations, and the resulting light-emitting diode exhibits an external quantum efficiency of 10.4% with suppressed efficiency roll-off. We reveal that the low-temperature crystallization process is due to the formation of low-dimensional intermediate states, and followed by interionic exchange. This work provides perspectives to tune phase transition pathway at low temperature for CsPbI3 device applications.

Highlights

Black phase CsPbI3 is attractive for optoelectronic devices, while usually it has a high formation energy and requires an annealing temperature of above 300 °C
We note that ZnO/polyethylenimine ethoxylated (PEIE) has been widely used as an electron transporting layer in perovskite LEDs27
The scanning electron microscopic (SEM) measurement shows that the imidazolium iodide (IZI)-CsPbI3 film is discrete, consisting of particles with an average size of ~80 nm (Fig. 1c)

Summary

Introduction

Black phase CsPbI3 is attractive for optoelectronic devices, while usually it has a high formation energy and requires an annealing temperature of above 300 °C. For CsPbI3-based light-emitting diodes (LEDs) applications, the low-temperature HI doping method is difficult to achieve high performance devices, mainly due to the high trap density and strong nonradiative recombination with those perovskite films (typical photoluminescence quantum efficiency (PLQE) < 1%)[20]. High-efficiency LEDs has been demonstrated based on CsPbI3 quantum dots (QDs)[21,22] Those colloidal QDs are synthesized ex situ in flasks by the hot-injection method, which usually requires a temperature above 170 °C and complicated processing conditions[21,22,23,24]. We reveal that the low-temperature formation process of black phase CsPbI3 can be generally observed when intermediate states are formed, followed by an interionic exchange in the presence of large organic ammonium cations

Methods

Results

Conclusion