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• Decreasing the carrier density of exciton formation zone benefits the stability of organic light-emitting diodes for electrically pumped organic lasers. • The carrier density has been modeled under high current injection via the model of carrier device lifetimes. • The carrier density decreases with the emissive layer's thickness increasing, but increases with the emissive layer's charge carrier mobilities. • The increase of the energetic disorder of emissive layer leads to a marked decrease of carrier density. • Increasing the charge carrier mobilities of hole and electron transport layers helps reduce carrier density. The carrier density in exciton formation zone is the electrical parameter most relevant to the stability of organic light-emitting diode: the decrease of carrier density improves the device stability. Here, based on the general mode of carrier device lifetimes, the carrier densities in the exciton formation zone of organic light-emitting diode have been calculated at current densities (J) ≥ 2.0 kA cm−2. With J increasing, the carrier density increases accordingly. At a given J , the carrier density decreases with the emissive layer's thickness increasing, but increases with the emissive layer's charge carrier mobilities. The increase of the energetic disorder of emissive layer leads to a marked decrease of carrier density. Increasing the hole (electron) mobility of hole (electron) transport layer helps reduce carrier density. The current research is believed very beneficial to the development of electrically pumped organic lasers. [ABSTRACT FROM AUTHOR]

• The width of exciton formation zone decreases with device current density increasing. • The width of exciton formation zone increases with emissive layer's thickness increasing. • An optimal charge mobility of emissive layer maximizes the width of exciton formation zone. • The width of exciton formation zone has certain correlation with the dielectric constant of emissive layer. • The width of exciton formation zone markedly increases with emissive layer's trap density increasing. The width of exciton formation zone has been simulated in a single-layer organic light emitting diode (OLED) based on the model of carrier device lifetimes. The width of exciton formation zone decreases with device current density increasing. Increasing the thickness of emissive layer (EML) is able to widen exciton formation zone. There is an optimal value of EML's charge carrier mobility to maximize the width of exciton formation zone. In addition, the width of exciton formation zone increases markedly with the trap density of EML increasing, and shows certain correlation with the dielectric constant of EML. The current modeling provides novel insights on optimizing EMLs towards wide exciton formation zone, helpful for extending operational stability of OLED. [ABSTRACT FROM AUTHOR]