The synergy of pre-frozen substrates and post-annealing for high-efficiency co-evaporated blue perovskite LEDs

The co-evaporation technique shows great potential for producing perovskite films. However, there is a lack of research on the growth process and the film characteristics of co-evaporated perovskite. Herein, we found that pre-frozen substrates and post-annealing can synergically improve the performance of co-evaporated blue perovskite light-emitting diodes (PeLEDs). The optimized blue PeLEDs obtained an impressive peak external quantum efficiency (EQE) of 7.2%, which is the best reported for co-evaporated blue PeLEDs till now. The systematic investigation found that the pre-frozen substrates can facilitate the exotherm of vaporized precursor molecules near the interface, leading to more efficient nucleation and constraining grain enlargement. Furthermore, low-temperature annealing (LTA) can efficiently suppress compositional segregation and release residual compressive strain in co-evaporated perovskite films while retaining the advantages of pre-frozen substrates. This work provided deeper insights into perovskite films prepared by co-evaporation and offered a feasible strategy for enhancing the performance of the co-evaporated PeLEDs.