Recent Progress in the Stability of Red-Emissive Perovskite Nanocrystals for Light-Emitting Diodes

Abstract

All-inorganic perovskite nanocrystals (PNCs) have been anticipated to be used in efficient and stable perovskite optoelectronic devices because of their suitable bandgap, broad absorption spectrum, and high color purity. However, long-term stability remains a major obstacle for the commercial application of PNCs. In particular, for red-emissive perovskites, the reaction to the environment is more sensitive than that for the green counterpart, which makes a phase transformation easily occur at room temperature. On the basis of CsPbI3 PNCs, we analyze the main instability factors of red-emissive PNCs (620–720 nm), including their structures, optoelectronic properties, and instability mechanism. We then summarize some strategies to improve the stability and performance of the perovskites and light-emitting diodes (LEDs). Furthermore, we discuss the challenge of scaling up the production of PNCs. Finally, we propose possible perspectives for the development of perovskite materials.

Filling Chlorine Vacancy with Bromine: A Two-Step Hot-Injection Approach Achieving Defect-Free Hybrid Halogen Perovskite Nanocrystals

“…When the bias voltage reaches over 8.0 V, the EL peak gradually shifts from 470 to 520 nm. Such a phenomenon is commonly observed in other mixed-halide perovskite LEDs, and it is believed to result from the phase segregation in the NC emissive layers. , However, we note that the present operational stability of the devices is considerably higher than those of early hybrid perovskite-based LEDs, which usually run under a 6.0 V safe voltage, above which a noticeable EL shift will occur because of the phase separation of Cl/Br perovskites. , This seems to be in line with the widely accepted notion that phase segregation rates are dictated by halide vacancy hopping barriers and are modulated by vacancy concentrations, namely, electric field-induced halide redistribution and phase separation can be greatly suppressed if halide vacancies are effectively passivated. , To further evaluate the operational stability of the ensuing LEDs, time-dependent EL measurement was performed, without using epoxy or silica encapsulation for protection. It is seen that EL spectra of the resulting LEDs retained 50% of the initial intensity after 120 min of continuous operation at 5.0 V while shortened to 70 min at 7.0 V (Figure S13).…”

“…Such a phenomenon is commonly observed in other mixed-halide perovskite LEDs, and it is believed to result from the phase segregation in the NC emissive layers. 49,51 However, we note that the present operational stability of the devices is considerably higher than those of early hybrid perovskite-based LEDs, which usually run under a 6.0 V safe voltage, above which a noticeable EL shift will occur because of the phase separation of Cl/Br perovskites. 52,53 This seems to be in line with the widely accepted notion that phase segregation rates are dictated by halide vacancy hopping barriers and are modulated by vacancy concentrations, namely, electric field-induced halide redistribution and phase separation can be greatly suppressed if halide vacancies are effectively passivated.…”

Deep-red and near-infrared light-emitting electrochemical cells employing perovskite color conversion layers with EQE >10%

“…42 Bulk CsPbI 3 has various phase structures (namely a, b, g, d) depending on the tilting or rotation of the octahedron (i.e., [PbI 6 ] 4À ). 47,48 These phases are stable at different temperatures. The a-phase (i.e., cubic phase) only exists at 4300 1C and the d-phase (i.e., orthorhombic phase) exists at room temperature.…”

“…The a-phase (i.e., cubic phase) only exists at 4300 1C and the d-phase (i.e., orthorhombic phase) exists at room temperature. 42,47,48 However, for CsPbI 3 nanocrystals, the a-phase can exist at room temperature. 42 The d-phase CsPbI 3 is a non-photoactive yellow phase 42,47,48 but a-, band g-phases are photoactive black phases.…”

Stabilizing red-emitting all-inorganic perovskite nanocrystals by a ligand-mediated room-temperature procedure

“…This is because the synthesis of red-emissive halide perovskite NCs is denoted as a "red wall" and a great challenge is faced when attempting to achieve stable iodinecontaining perovskite NCs and stable emissions in the red spectral ranges. 14 The reaction of red-emitting perovskites to the ambient environment is more sensitive than that of their green counterpart, 15 leading to poorer stability and easier degradation of red-emissive perovskite materials under heat, light illumination, and moisture attack. The stability enhancement for iodine-based red-emitting NCs which could also be promising as a commercial red phosphor 16,17 needs to be further explored.…”