Researchers in Sweden and China have studied the reasons behind the short operational lifetime of blue perovskite-based LEDs (PeLEDs).
While perovskite light-emitting diodes (PeLEDs) have seen unprecedented development in device efficiency over the past decade, they still suffer from poor operational stability. This is especially true for blue PeLEDs, whose operational lifetime remains orders of magnitude behind their green and red counterparts. The scientists in this work have systematically investigated this efficiency-stability discrepancy in a series of green- to blue-emitting PeLEDs based on mixed Br/Cl-perovskites. Typically, mixed chloride/bromide perovskites are employed to produce ideal blue emission. However, the researchers have uncovered a counterintuitive fact: even minute quantities of chloride loading can have a dramatic negative impact on the operational lifetime of these devices.
They also found that such an issue is an intrinsic problem that chloride ions are of a very low migration energy barrier in mixed bromide/ chloride perovskites, making them rapidly leave perovskite films under electrical bias. Device lifetime drops exponentially with increasing Cl-content, accompanied by an increased rate of change in electrical properties during operation. The team ascribes this phenomenon to an increased mobility of halogen ions in the mixed-halide lattice due to an increased chemically and structurally disordered landscape with reduced migration barriers. Their results indicate that the stability enhancement for PeLEDs might require different strategies from those used for improving efficiency.