Generalization of the two-diode IV model for background-doped thermophotonic LEDs

In recent work, shifted-junction LEDs were developed that yield extremely low non-radiative losses. However, their IV curves show features that standard two-diode models cannot explain. In this work, these features are described using a generalization of the two-diode model that employs a non-radiative current starting at an ideality factor n_id=1, that saturates to n_id=2 behavior beyond a threshold voltage. This saturating diode (SD) model works particularly well for IV curves that show neither a clear n_id=1 or n_id=2 regime. The SD model is verified using drift–diffusion simulations and measured IV curves of shifted-junction LEDs. Subsequently, this framework is applied to establish the radiative current and coupling efficiency required to reach wall-plug efficiencies surpassing unity, which is required for electroluminescent cooling. Specifically, it is demonstrated that the device parameters required to reach the cooling regime have all been achieved separately, albeit in different devices, assuming the radiative current changes in line with what is expected at high light extraction efficiencies from previous numerical studies.