Boosting the external quantum efficiency in perovskite light-emitting diodes by an exciton retrieving layer
Perovskite light-emitting diodes (PeLEDs) are promising next-generation light sources due to the excellent optical and electronic properties of the materials as well as their process simplicity and low cost. To boost their electroluminescence (EL) efficiency, a plethora of approaches are proposed and demonstrated. Here, another possibility by introducing an exciton retrieving layer (ERL) into the devices is reported. A composite layer, formed by vacuum co-evaporating an electron transporting material (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, TmPyPB) and a blue phosphorescent material (bis(2-(4,6-difluorophenyl)-pyridinato-N,C2′)picolinate, FIrpic), is inserted into PeLEDs as an ERL in between the emitting layer and the electron transporting layer. Both 3D and quasi-2D PeLEDs with an ERL exhibit strongly enhanced EL performance without changing the emission spectra. 3D PeLEDs show a low turn-on voltage of ∼3.6 V, a maximum luminance of 14 363 cd m−2, and a maximum external quantum efficiency (EQE) of 1.26%, which correspond to 2.5-fold luminance and 3.8-fold EQE enhancements compared with the control device. Quasi-2D PeLEDs exhibit a low turn-on voltage of ∼3.6 V, a maximum luminance of 9481 cd m−2, and a maximum EQE of 4.24%, corresponding to a 2.7-fold EQE enhancement compared with the control device. The physical mechanism is further discussed theoretically and validated experimentally. The blue phosphorescent FIrpic can act as a sensitizer such that energy can be transferred from both the singlet and triplet excitons of TmPyPB to the excited states of CsPbBr3via Förster and Dexter energy transfer processes.