Abstract
SummaryThis paper reports a new method to generate stable and high-brightness electroluminescence (EL) by subsequently growing large/small grains at micro/nano scales with the configuration of attaching small grains on the surfaces of large grains in perovskite (MAPbBr3) films by mixing two precursor solutions (PbBr2 + MABr and Pb(Ac)2·3H2O + MABr). Consequently, the small and large grains serve, respectively, as passivation agents and light-emitting centers, enabling self-passivation on the defects located on the surfaces of light-emitting large grains. Furthermore, the light-emitting states become linearly polarized with maximal polarization of 30.8%, demonstrating a very stable light emission (49,119 cd/m2 with EQE = 11.31%) and a lower turn-on bias (1.9 V) than the bandgap (2.25V) in the perovskite LEDs (ITO/PEDOT:PSS/MAPbBr3/TPBi[50 nm]/LiF[0.7 nm]/Ag). Therefore, mixing large/small grains with the configuration of attaching small grains on the surfaces of large grains by mixing two precursor solutions presents a new strategy to develop high-performance perovskite LEDs.
Highlights
In the precursor containing PbBr2 and MABr with DMF as solvent, these two strong electrolytes can dissociate into Pb2+, MA+, and BrÀ ions, enabling very fast crystallization to quickly grow large grains as large as several micrometers during spin-coating before thermal annealing, indicated by the scanning electron microscope (SEM) image in Figure 1A and atomic force microscopy (AFM) images
The longer PL lifetime observed from mixed large/small grains provides an evidence that attaching small grains to the surfaces of large grains introduces an interaction between large- and small-grain components toward self-passivation
Owing to bandgap offset between small grains and large grains, carrier transfer from small grains to large iScience 19, 378–387, September 27, 2019 379
Summary
Organic metal halide perovskites have become attractive candidates to develop thin-film light-emitting devices (LEDs) with low turn-on voltage (Wang et al, 2015; Meng et al, 2017), ambipolar transport (Shi et al, 2015; Stranks et al, 2013), large color-tuning properties (Xing et al, 2014; Tan et al, 2014; Protesescu et al, 2015), and high device efficiencies (Kim et al, 2015; Li et al, 2015; Xing et al, 2016; Yu et al, 2016; Ning et al, 2015; Wang et al, 2016a; Deschler et al, 2014; Sutherland and Sargent, 2016). Controlling grain boundary defects becomes a critical procedure to develop highly efficient perovskite LEDs. In general, there are two different ways to control grain boundary defects: (1) extrinsic method through doping or thermal/solvent treatment (Hadadian et al, 2016; Wang et al, 2016b) and (2) intrinsic method by using self-passivation during device operation (Bi et al, 2017). The recent studies have shown an extrinsic approach to constrain the mobile ions by introducing polymer chains into polycrystalline perovskites (FAPbBr3), which leads to a high electroluminescence (EL) efficiency (14.36%) (Yang et al, 2018). Controlling mobile ions becomes a critical procedure to develop high-performance perovskite LEDs
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