Modification of interface between PEDOT:PSS and perovskite film inserting an ultrathin LiF layer for enhancing efficiency of perovskite light-emitting diodes

PEDOT:PSS has been widely used in perovskite light-emitting diodes (PeLEDs) due to its high hole current conductivity and work function. However, the unbalanced charge injection and severe exciton quenching in PEDOT:PSS restrict the EL performance of PeLEDs. In this work, a facile interface modification method is introduced in which an ultrathin LiF layer is inserted at the interface between PEDOT:PSS and MAPBBr3 perovskite film. Our results indicate that the inserted ultrathin LiF layer contributes to an efficient interface passivation effect between the PEDOT:PSS layer and the perovskite film, which significantly suppresses both the exciton quenching by the conductive PEDOT chains and the perovskite film defect density at the interface. Moreover, balanced charge injection is realized by adjusting the thickness of the LiF layer, which also serves as an electron blocking layer, in order to preferentially hinder electron current over hole current. Consequently, the optimal PeLED with a 2 nm LiF layer exhibits a significantly decreased turn-on voltage of 2.8 V compared to 4.9 V of the pristine device without a LiF layer, combined with an over 100-fold enhancement in the maximum luminance (10415 cd/m2), current efficiency (12.1 cd/A), and external quantum efficiency (3.5%).