Dynamic Redistribution of Mobile Ions in Perovskite Light‐Emitting Diodes

Abstract

Despite quick development of perovskite light‐emitting diodes (PeLEDs) during the past few years, the fundamental mechanisms on how ion migration affects device efficiency and stability remain unclear. Here, it is demonstrated that the dynamic redistribution of mobile ions in the emissive layer plays a key role in the performance of PeLEDs and can explain a range of abnormal behaviours commonly observed during the device measurement. The dynamic redistribution of mobile ions changes charge–carrier injection and leads to increased recombination current; at the same time, the ion redistribution also changes charge transport and results in decreased shunt resistance current. As a result, the PeLEDs show hysteresis in external quantum efficiencies (EQEs) and radiance, that is, higher EQEs and radiance during the reverse voltage scan than during the forward scan. In addition, the changes on charge injection and transport induced by the ion redistribution also well explain the rise of the EQE/radiance values under constant driving voltages. The argument is further rationalized by adding extra formamidinium iodide (FAI) into optimized PeLEDs based on FAPbI3, resulting in more significant hysteresis and shorter operational stability of the PeLEDs.

Degradation and self-repairing in perovskite light-emitting diodes

“…Hence, this leads to more severe J-V hysteresis upon scan direction in half-degraded devices (Figure S8). 2,39 The slightly enhanced ion migration could be a result of newly formed defects that provide more hopping sites for ionic species. 40,41 All the detailed parameters for mobile ions are summarized in Table S1.…”

Improved highly efficient Dion–Jacobson type perovskite light-emitting diodes by effective surface polarization architecture

“…35 It is commonly accepted that the role of ions in perovskite cannot be ignored in all perovskite devices. 36,37 Under the forward bias applied, the ions should be redistributed under the change in electric field. The anions could migrate and accumulate at the interface between the perovskite and hole transport layer (TFB in our structure) to lift the Fermi level and reduce the injection barrier by ion-induced surface polarization.…”

Ion Motion Determines Multiphase Performance Dynamics of Perovskite LEDs

“…[34] A similar conclusion that redistribution of iodine defects causes reversible variations of current and EL intensity on a timescale of seconds has been also recently suggested by analyzing performance hysteresis of FAPbI 3 PeLEDs. [11] According to Buin et al, positively charged iodine vacancies V i + should be the most mobile charged iodine defects. [17] However, our samples were prepared under iodine-rich conditions from solution with 20 mol% excess PMAI (benyzlammonium iodide), which suggests that iodine interstitials inside the bulk of crystallites or iodine ions at the crystallite boundaries should be dominating defects.…”

“…PeLEDs also suffer from efficiency rolloff limiting their brightness. [7][8][9][10] Another issue, particularly important for the highspeed device operation, is the occurrence of hysteresis [1,11] and variations of the electroluminescence (EL) EQE and photoluminescence (PL) efficiency [3,12] under electrical stress.The performance hysteresis in perovskite solar cells was widely investigated and was attributed to the changes of perovskite-transport layer interfaces or to the motion of mobile ions. [13][14][15][16] Ion motion in metal-halide perovskites is a very complex and still poorly understood phenomenon.…”

“…PeLEDs also suffer from efficiency rolloff limiting their brightness. [7][8][9][10] Another issue, particularly important for the highspeed device operation, is the occurrence of hysteresis [1,11] and variations of the electroluminescence (EL) EQE and photoluminescence (PL) efficiency [3,12] under electrical stress.…”