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A simple analytical model for p-i-n light-emitting diodes is presented to give insight into the device physics. The 1-D model describes the dc electrical characteristics and internal quantum efficiency (ηIQE) as a function of the applied bias and is in good agreement with TCAD simulations. An optimization scheme, based on the same model, shows improved ηIQE for engineered heterojunctions by reducing the diffusion current contribution. The results show that the use of heterojunctions increases the light intensity inside a narrow-bandgap material, akin to the experimentally observed results. The bandgap of the active region determines the voltage at which the maximum efficiency occurs. It is also shown that maximum ηIQE occurs at a lower bias than that typically used for studying the maximum light intensity. The effect of injection dependence of recombination coefficients on the efficiency is also studied. For the first time, the electrical performance of a multilayer active region is modeled.