To reveal the degradation mechanism of 3D perovskite, we used FAPbI3 as a model system and fabricated perovskite LEDs. By performing the simultaneous measurement of PL and electroluminescence (EL) on working LEDs, excitation-intensity-dependent photoluminescence quantum efficiencies (PLQEs) measurement and PL measurement of FAPbI3 film heated at different temperatures, the effects of Auger recombination and Joule heating on device stability were all excluded, suggesting the ion migration of 3D FAPbI3 perovskites under electrical stress is the main reason for device degradation and efficiency roll-off. Based on this understanding, we introduced a bifunctional-molecule 3-chlorobenzylamine (3Cl-BA) additive into the perovskite precursor solution to assist the oriented growth of perovskites through both the amino and chloride groups. This results in near-infrared perovskite LEDs with a peak external quantum efficiency of 16.6%, which sustains 80% of its peak value at a high current density of 460 mA cm-2. Moreover, the device reaches a record half-lifetime of 49 h at room temperature under a constant current density of 100 mA cm-2.
Furthermore, to verify the phase segregation issue in mixed-halide perovskites, by using high-resolution cathodoluminescence microscopy, we directly revealed that the phase segregation in mixed-halide perovskite is caused by the intrinsic and microscopical phase heterogeneity in as-deposited perovskite films, which is resulted from precursor solution with nonuniform mixture of halides. The first-principles calculations indicate that the halide separation in the as-made materials predisposes to undergo much more substantial halide segregation under electrical excitation in LEDs, whereas the more uniform initial halide distribution materials are much more resistant to subsequent halide segregation. Therefore, uniform initial mixed-halide perovskite material is essential for stable perovskite LEDs.
The project results will be disseminated via publications, conference and public engagement. One work has been submitted to Nature Communications and the other manuscript is planned to be submitted to Advanced Materials. Due to the Covid-19 situation, the researcher took some online conferences, including the Translational Perovskite e-conference. For commercialization, the University of Cambridge has a dedicated office (Cambridge Enterprise) for the commercialization of research, which has a very successful track record in transferring technology from lab to industry. Also, the host group has close collaboration with the company of Heliochrome Ltd, which was set up to develop light-emitting devices made with lead halide perovskites and related materials.
