Conjugated Alkylamine by Two‐Step Surface Ligand Engineering in CsPbBr₃ Perovskite Nanocrystals for Efficient Light‐Emitting Diodes

Abstract

Long alkyl‐chain capped ligands are prerequisites for preserving high photoluminescence quantum yield (PLQY) in perovskite nanocrystals (NCs). Unfortunately, the insulating feature of surface ligands potentially hinders carrier transport in light‐emitting diode (LED) devices, which will degenerate the LED performance. To overcome this shortcoming, we introduce a conjugated molecule, 3‐phenyl‐2‐propen‐1‐amine (PPA), into CsPbBr3 NCs through a two‐step surface ligand engineering process. Owing to excellent electrical conductivity of PPA, PPA‐capped CsPbBr3 NCs LEDs exhibit a maximum current efficiency of 23.53 cd A−1, and a maximum luminance of 26,475 cd m−2 at the wavelength of 517 nm. This work offers a new strategy to improve the quality of CsPbBr3 NCs and LEDs by introducing conjugation molecular ligands into the all‐inorganic perovskite nanocrystals.

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

“…( 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.…”

All-Inorganic Perovskite Solar Cells Based on CsPbIBr2 and Metal Oxide Transport Layers with Improved Stability

“…In recent years, cesium lead halide or mixed halide perovskites CsPbX 3 have attracted much attention as light absorbent layer materials due to their excellent thermal stability as well as suitable photophysical properties [4][5][6]. In particular, the CsPbIBr 2 have emerged as a better candidate among its cousins, because of its capacity to balance the bandgap and its thermal stability [7], which has a bandgap of 2.05 eV, promising a potential highest PCE about 17.5% according to the Shockley-Queisser limit [8] and the material is unexpectedly stable with a melting point more than 460 • C under ambient atmosphere [9]. The higher performance PSCs usually have a sandwich structure, in which the 2 of 10 perovskite active layer is placed between a hole transport layer (HTL) and an electron transport layer (ETL).…”