Metal halide perovskites (MHPs) have attracted attention as light emitters due to high color purity (full width at half maximum ~20 nm), low material cost, solution processibility and tunable bandgap. However, perovskite light-emitting diodes (PeLEDs) suffer from poor stability due to degradation by moisture1 and ion migration of perovskite component2. One of the method to overcome these problems is polymer incorporation method, because polymer can effectively prevent ion migration and degradation by moisture. Even though current efficiency (CE) of 21.38 cd/A and external quantum efficiency (EQE) of 4.76% were achieved by polymer incorporation method3, studies concerning ion migration and air stability are still lacking.
Here, we present highly efficient and stable PeLEDs achieved by incorporating polymer additives and investigation regarding ion migration and air stability. Various kinds of polymers that have lone pair electrons were used to passivate Pb2+ atoms which act as non-radiative recombination center. To identify whether Pb2+ atoms were passivated or not, photoluminescence (PL) and transient photoluminescence (TRPL) were implemented. PL intensity and PL lifetime were dramatically enhanced with polymer additives, which can be attributed to passivation of trap states. To further investigate interaction between polymer additives and perovskites, fourier-transform infrared spectroscopy (FT-IR) and ultraviolet photoelectron spectroscopy (UPS) were implemented. Also, as the polymer impedes the diffusion of perovskite precursor during crystallization, the grain size was decreased, confirmed by scanning Electron Microscopy (SEM) and atomic force microscopy (AFM). This result can also lead to improved luminescent property, by improving special confinement of exciton or free carrier from decreased grain size. Considering the low stability of perovskite emitters, time-dependent electroluminescence and J-V-L measurement were also conducted to figure out effect of polymer additives on air stability and ion migration, respectively. Finally, the device efficiency can be improved by polymer additives, confirmed by J-V-L characteristics. In conclusion, our work has shown that polymer incorporation method can improve device performance and stability. Thus it will contribute to development and commercialization of PeLEDs.
1. Yang, S., Wang, Y., Liu, P., Cheng, Y., Zhao, H. J., & Yang, H. G. (2016). Functionalization of perovskite thin films with moisture-tolerant molecules. Nat. Energy, 1(2), 15016.
2. Azpiroz, J. M., Mosconi, E., Bisquert, J., & Angelis, F. D. (2015). Defect migration in methylammonium lead iodide and its role in perovskite solar cell operation. Energy Environ. Sci., 8(7), 2118-2127.
3. C. Wu, Y. Zou, T. Wu, M. Ban, V. Pecunia, Y. Han, Q. Liu, T. Song, S. Duhm, B. Sun. (2017). Improved Performance and Stability of All-inorganic Perovskite Light-Emitting Diodes by Antisolvent Vapor Treatment. Adv. Funct. Mat, 27, 1700338.