Showerhead-assisted chemical vapor deposition of CsPbBr3 films for LED applications

Abstract

CsPbBr3 represents a highly attractive material for perovskite light-emitting diodes (PeLEDs) in the green spectral range. However, the lack of deposition tools for reproducible and scalable growth of perovskite films is one of the major obstacles hindering PeLED commercialization. Here, we employ the highly scalable showerhead-assisted chemical vapor deposition (CVD) method to produce uniform pinhole-free CsPbBr3 films for PeLED application. The precursors CsBr and PbBr2 are evaporated under low vacuum in N2 carrier gas. By adjusting the PbBr2 sublimation temperature, process conditions for CsBr-rich, stoichiometric, and PbBr2-rich CsPbBr3 layer growth have been developed. A substrate temperature of 160 °C enables direct growth of these CsPbBr3 films on a polymeric hole transport layer (HTL), finally yielding PeLEDs with a maximum luminance of 125 cd/m2. Although the device efficiency still lags behind solution-processed counterparts, our approach presents the first demonstration of PeLEDs containing CsPbBr3 films processed in a perovskite showerhead-assisted CVD reactor. Graphic abstract

Perovskite Light‐Emitting Diodes with an External Quantum Efficiency Exceeding 30%

“…Meanwhile, some other excess electrons accumulate at the HTL/EML interface (Figure 1d), which leads to increased nonradiative recombination. [ 41 ] Hence, in operational PeLEDs, exciton formation in the PVK or accumulation at the interface suggests electron leakage, that is, electron transfer from the perovskites to the PVK or the interface, causing reduced efficiency.…”

“…The PeLED (Device-I) shows relatively poor performance with a maximum EQE of 17.08% and a maximum current density (CE) of 75.40 cd A −1 (Figure 1a; Figure S2a, Supporting Information), which is almost consistent with the literature reports. [38][39][40][41] We built hole-only and electronic-only devices to understand the charge carrier transport properties. The current density-voltage curves (Figure S2b-d, Supporting Information) were analyzed by the Mott-Gurney and Poole-Frenkel laws (details in Supporting Information) to obtain the field-dependent charge carrier mobilities, which demonstrate that the electrons (Figure 1b) show much higher carrier mobility than the holes.…”

Vacuum Processed Metal Halide Perovskite Light‐Emitting Diodes

“…A simplified flow diagram of CVD is shown in Figure a. [ 55 ] In a typical setup, CVD is performed in a tube furnace with strict control of temperature, gas environment, and flow rate. Two gas streams loaded with evaporation precursors are impinged vertically and combined in a static forced mixing unit, with a high‐temperature exhaust system to prevent unwanted deposition during the heating and cooling stages.…”

“…A highly scalable showerhead‐assisted CVD method was applied to produce uniform pinhole‐free CsPbBr 3 films for LED applications by Sanders et al [ 55 ] As shown in the SEM images in Figure 7d, all CVD layers are entirely closed, which is necessary to prevent short circuits in the PeLED stack. Unlike solution processing, the CVD process does not require any pretreatment, thus providing greater flexibility in the choice of novel electrode substrates and charge carrier transport films for PeLEDs.…”

“…e) L-V curves of PeLED with a CsPbBr 3 layer processed by CVD and spin-coating. Figure7a,d,e is reproduced with permission [55]. Copyright 2021, Springer Nature.…”