Quantum dot based light-emitting electrochemical cells

Abstract

Quantum dots (QDs) have cemented their position in lighting applications due to their outstanding optical properties, color purity with narrow emission spectrum, and solution processability. Recently, they have been introduced into light-emitting electrochemical cells (LECs). This system represents a promising large-area device concept based on solution fabrication procedures and air-stable electrode materials. LECs based on CdSe/CdS core/shell QDs achieve bright, uniform and highly voltage-independent electroluminescence with maximum brightness up to 1000 cd/m2 and current efficiencies of 1.9 cd/A; comparable with multilayer QD-based light-emitting diodes (LEDs). However, some limitations still need to be overcome: The decrease in photoluminescence quantum yield (ϕ) after the ligand-exchange step and the unstable blue emission. Recently emerged hybrid organic-inorganic or fully inorganic perovskite nanocrystals (NCs) do not suffer from these undesirable features. Unlike core/shell QDs, they show high ϕ without surface passivation, tunable band gaps via quantum confinement or simple changes in composition, and also show no spectral broadening from high surface trap densities. All these characteristics make perovskite QDs a very competitive alternative as the emitting material in LECs.