Elucidating and Mitigating Degradation Processes in Perovskite Light-Emitting Diodes

Halide perovskites have attracted substantial interest for their potential as disruptive display and lighting technologies. However, perovskite light-emitting diodes (PeLEDs) are still hindered by poor operational stability. A fundamental understanding of the degradation processes is lacking but will be key to mitigating these pathways. Here, we use a combination of in operando and ex-situ measurements to monitor the performance degradation of (Cs0.06FA0.79MA0.15)Pb(I0.85Br0.15)3 PeLEDs over time. Through device, nanoscale cross-sectional chemical mapping, and optical spectroscopy measurements, we reveal that the degraded performance arises from an irreversible accumulation of bromide content at one interface, which leads to barriers to injection of charge carriers and thus increased non-radiative recombination. We impede this ionic segregation by passivating the perovskite films with potassium halides, which immobilizes the excess halide species. The passivated PeLEDs show enhanced external quantum efficiency (EQE) from 0.5 to 4.5% and, importantly, show significantly enhanced stability, with minimal performance roll-off even at high current densities (> 200 mA/cm2). The decay half-life for the devices under continuous operation at peak EQE increases from <1 hour to ~15 hours through passivation, and ~200 hours under pulsed operation. Our results provide generalized insight into degradation pathways in PeLEDs and highlight routes to overcome these challenges.The authors thank the Engineering and Physical Sciences Research Council (EPSRC) for support (EP/R023980/1). Z.A.-G. acknowledges funding from a Winton Studentship, and ICON Studentship from the Lloyd’s Register Foundation. S.D.S acknowledge the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, Grant Agreement No. 756962), and the Royal Society and Tata Group (UF150033). M.A.-J. thanks Cambridge Materials Limited, Wolfson College, University of Cambridge, and EPSRC for their funding and technical support. F.U.K. thanks the Jardine Foundation and Cambridge Trust for a doctoral scholarship. This work was carried out with the support of the Diamond Light Source, instrument I09 (proposal SI22668-1). The research leading to this result has been supported by the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. H.R., G.J.M. and U.B.C. acknowledge research funding from the Swedish Research Council (Grant nos. VR 2018-04125, 2018-06465, and 2018-04330), the Swedish Foundation for Strategic Research (Project no. RMA15-0130) and the Swedish Energy Agency (Grant no. P43549-1)