High performance sky-blue perovskite light-emitting diodes enabled by a bifunctional phosphate molecule

Abstract

Defects such as uncoordinated lead ions and surface charged defects are still one of critical issues for perovskite light-emitting diodes (PeLEDs). The presence of these defects can trap excitons, resulting in enhanced nonradiative recombination and thus poor efficiencies of PeLEDs. Defect passivation via passivation agents is an effective way to solve this issue. In this work, we introduce a bifunctional phosphate molecule 6,6′-(ethane-1,2-diyl)bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (DIDOPO) as a passivation agent into the perovskite, where DIDOPO can bind with the perovskite via the chemical interaction between the PO groups and uncoordinated Pb ions. Thus, the incorporation of DIDOPO effectively passivates the defects, leading to improved radiative recombination. Simultaneously, the as-prepared perovskite film produces dense and smooth morphology, which is favorable to good contact with the adjacent charge transport layers and the reduction of leakage current. As a result, the sky-blue PeLEDs modified by DIDOPO show improved efficiency with the maximum external quantum efficiency (EQEmax) of 5.52% and the average EQEmax of 5.09%. Furthermore, attributed to the alkyl chain as the bridge between the phosphate groups, DIDOPO accumulated at the perovskite surface is able to decrease hydrophilic behavior of the perovskite. The PeLEDs containing DIDOPO possess enhanced moisture resistance, remaining ca. 91–92% of the initial EQE after storage for 120 h in ambient atmosphere with the humidity of ca. 40%.