We propose a model for quantum dot light emitting devices (QD-LEDs), which explores the most important parameters that control their electrical characteristics. The device is divided into a hole transport layer, several quantum dot layers, and an electron transport layer. Conduction and recombination in the central quantum dot region is described by a system of coupled rate equations, and the drift-diffusion approximation is used for the hole and electron transport layers. For NiO/Si-QDs/ZnO devices with suitable design parameter, the current and light output are primarily controlled by the quantum dot layers, specifically, their radiative and non-radiative recombination coefficients. Radiative recombination limits the device current only at sufficiently large bias.