Theoretical model and simulation of carrier heating with effects of nonequilibrium hot phonons in semiconductor photovoltaic devices

A theoretical model and its rate equations of carrier number and energy densities are proposed and presented for calculating carrier heating in semiconductor photovoltaic devices. The rate equation for carrier number density is the Shockley‐Queisser theoretical model, while the rate equation for carrier energy density includes the carrier interband energy relaxation via radiative recombination and the intraband energy relaxation via the interactions between carriers and polar longitudinal optical phonons. The carrier intraband energy relaxation is calculated by incorporating the effects of nonequilibrium hot phonons and the Thomas‐Fermi static screening. This model and its rate equations are employed for numerical simulations of the magnitude of carrier heating and its effects on the current‐voltage relations of bulk GaAs solar cells under different concentration ratios and with different widths of the active region. The simulation results demonstrate that carrier temperature in general heats up to 400 to 900 K at short‐circuit operating condition. This carrier heating cools down to lattice temperature when the device approaches its open‐circuit point. Based on these numerical results, effects of carrier heating on the performance of conventional solar cells and also their implications for the design of hot‐carrier solar cells will be discussed. In this work, the magnitude of carrier heating in semiconductor photovoltaic devices is calculated by considering the intraband carrier energy relaxation via the carrier‐polar‐longitudinal‐optical‐phonon interactions with the effects of nonequilibrium hot phonons and the Thomas‐Fermi static screening. The simulation results demonstrate that the incident sunlight, even without a solar concentrator, provides enough power to the device to establish the condition of hot carriers when the device operates close to its short‐circuit condition.