A mixed solvent strategy enabling efficient all-solution-processed perovskite light-emitting diodes

Abstract

Due to the ionic feature of perovskites, the fabrication of perovskite light-emitting diodes (PeLEDs) is highly dependent on vacuum deposition technology to construct solid perovskite/charge transport layer (CTL) heterojunctions and avoid the destruction of the perovskite layer by solvents of the upper solution-processed CTLs. Herein, we employ a mixture of chlorobenzene (CB) and dichloromethane (DCM) with distinctive boiling points as an orthogonal solvent for the polyfluorene poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) when depositing the upper electron transport layer (ETL) on the perovskite layer. By adjusting the ratios of CB and DCM, smooth and dense PFN films are obtained due to the effective control over the solvent evaporation rates. Moreover, the work function of PFN dissolved in the orthogonal solvent with an optimal volume ratio of CB and DCM is downshifted on account of the large dielectric constant of DCM, which results in a high dipole moment at the PFN/perovskite interface, thus reducing the charge transfer between the perovskite and PFN films. As a result, we achieve an efficient all-solution-processed PeLED with a champion EQE of 4.76% and a maximum luminance of 19 750 cd m⁻² at 513 nm. Our work provides a facile strategy to realize high-performance all-solution-processed PeLEDs.