Photovoltaic & Optoelectronic Device Group

Abstract:

Although significant progress has been made in the development of green, red, and near-infrared perovskite light-emitting diodes (PeLEDs), blue PeLEDs exhibit inferior performance, owing to various defects and poor carrier injection in solution-processed perovskite films. Thus, this study incorporates dual-passivation additive diphenylphosphinamide (DPPA) into perovskite films, and through density functional theory calculations and experimental characterizations, DPPA has been proven to be an effective passivator. Its phosphine oxide group coordinates with unsaturated lead ions, passivating perovskite defects, while the amino group forms hydrogen bonds with adjacent halide ions, suppressing their migration and further strengthening the passivation effect. Blue quasi-two-dimensional PeLEDs based on DPPA-modified perovskite films achieved an external quantum efficiency of 12.31% with an emission peak at 486 nm. Moreover, the device operational lifetime was extended by 32% with more stable spectra owing to the decreased defect density and suppressed ion migration in the perovskite film.

Abstract:

Despite the enormous developments in perovskite light-emitting diodes (PeLEDs) recently, obtaining efficient blue PeLEDs is still considered a critical challenge due to the non-radiative recombination and unbalanced charge injection caused by the unmatched carrier mobility and the deep hole-injection barrier between the hole-transport layer (HTL) and the emissive layer (EML). Herein, we incorporate tris(4-trifluoromethylphenyl)phosphine oxide (TMFPPO), obtained through a facile oxidation synthesis process, into poly(9-vinylcarbazole) (PVK). TMFPPO incorporation modulated the energy level and hole mobility of the binary-blend HTLs to eliminate the hole-injection barrier and balance the charge injection within the EML. Consequently, the blue PeLEDs with blended HTL presented an external quantum efficiency (EQE) of 7.23% centred at 477 nm, which was much higher than the EQE of a PVK device (4.95%). Our results demonstrate that modulating the energy level and charge injection of the HTL in the device is a promising method for obtaining efficient blue PeLEDs.