Efficient perovskite nanocrystal light-emitting diodes using a benzimidazole-substituted anthracene derivative as the electron transport material

Abstract

We report efficient perovskite nanocrystal LEDs based on a new electron transport material, BBIA, possessing high electron mobility of 4.17 × 10−4 cm2 V−1 s−1. BBIA-based devices exhibit a nearly two-fold enhancement than TPBi counterpart.

Light Generation in Lead Halide Perovskite Nanocrystals: LEDs, Color Converters, Lasers, and Other Applications

“…The charge carrier balance in the recombination zone is another important factor in determining the EQE, which is consistent with the role played by the emissive film PLQY . For an LHP‐NC LED driven by imbalanced charge carriers in the recombination zone, the excess carrier species are themselves the loss, and the resulting interaction with excitons leads to an additional loss, even at a low driving current density, via the Auger nonradiative process.…”

“…( Table 1 ). Electrical driving almost does not change the superior optical features of LHP‐NCs as emitters in the resulting LEDs, including their high color purity, a wide color gamut, and a stable spectrum that is independent of the applied driving voltage . Under electrical excitation, LHP‐NCs consisting of mixed halides would undergo spectral splitting; however, RGB primary color LEDs that use single‐halide LHP‐NC emitters still exhibit a wide color gamut that can display most natural colors in resulting full color displays.…”

“…Several factors lead to EQE losses in operating LHP‐NC LEDs, including the intrinsic characteristics of LHP‐NC emitters and extrinsic loss that depend on the device structure. The intrinsic EQE loss in LHP‐NCs typically includes two contributions to nonradiative recombination: trap states and the Auger process . As a planar device structure limits the low photon outcoupling efficiency to ≈20%, the PLQY of the LHP‐NC film plays an ultimate role in determining the maximum EQE that resulting LEDs can achieve .…”

“…As a planar device structure limits the low photon outcoupling efficiency to ≈20%, the PLQY of the LHP‐NC film plays an ultimate role in determining the maximum EQE that resulting LEDs can achieve . A high defect tolerance does not correspond to the absence of the resulting EQE loss, which is consistent with a low initial EQE at a low driving current density level; thus, a high‐quality LHP‐NCs emitter film with a low defect density is required to suppress the EQE loss from trap‐mediated nonradiative recombination. Unlike trap‐assisted nonradiative recombination, which occurs at all excitation levels, the EQE loss from a multiexciton Auger process only occurs at high excitation levels, which is more applicable to EQE droop at high driving current densities in LEDs and proof‐of‐principle electrically pumped lasing studies.…”

“…The extrinsic factors resulting in EQE loss are related to the device structure and include the leakage current and imbalanced charge carriers . In an LED with a low‐quality LHP‐NC film and charge carrier transport layers with many bandgap states, the injected charge carriers would flow across the device via these trap states even if the device is still in an off‐state under a bias lower than the threshold . Nonuniformity in an LHP‐NC film is another source of leakage current.…”