Stable, Efficient Near-Infrared Light-Emitting Diodes Enabled by α/δ Phase Modulation.

Although formamidinium lead iodide (FAPbI) perovskite shows excellent prospects in the field of optoelectronics, it is limited by the conversion of the black perovskite phase (α-FAPbI) to the yellow non-perovskite phase (δ-FAPbI). Here, we first introduce diamine cations [EDBE, 2,2-(ethylenedioxy)bis(ethylamine)] into FAPbI for stable and efficient near-infrared perovskite light-emitting diodes (NIR PeLEDs). By rationally regulating the α/δ phase, we have successfully prepared a NIR PeLED with an external quantum efficiency (EQE) of ≤11.40%. In addition, the perovskite film has excellent stability and does not undergo any significant change after being in air for 270 days. These results show that the introduction of EDBE reduces the formation energy of α-FAPbI perovskite and the hydrogen bonds formed between adjacent EDBE molecules increase the stability of the perovskite devices. This work could help guide the phase transition mechanism of FAPbI and further improve the performance of LEDs.