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

Abstract

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.

The effects of intraband and interband carrier‐carrier scattering on hot‐carrier solar cells: A theoretical study of spectral hole burning, electron‐hole energy transfer, Auger recombination, and impact ionization generation

“…In addition, the electron and hole temperatures of a solar cell are determined by many factors, such as the solar concentration ratio, the size of the device, and the operating point of the device. As has been shown in a previous study,14 the electron temperature of a conventional GaAs solar cell near a short-circuit condition can be 400 to 900 K.…”

“…However, if the device operates at near the short-circuit point with a carrier temperature of 1300 K, the hot-carrier-enhanced Auger recombination will become significant and its J Aug /μm will be smaller yet comparable with the J SQ sc . Nonetheless, according to the simulation results, 14 carriers in conventional GaAs solar cells can only reach such degree of carrier heating for devices with a very small width of the active region operating with a high degree of solar concentration. In short, for conventional GaAs solar cells operating as in the SQ model, the effect of Auger recombination on their efficiency can be noticeable but not significant.…”

“…Since issues related to the carrier temperature are usually less of a concern in conventional solar cells, the effects of intraband carrier‐carrier scattering are usually presumed to be negligible. However, a recent theoretical study has suggested that carrier temperatures can be significantly higher than the lattice temperatures in conventional solar cells, especially when photovoltaic devices operate near a short‐circuit condition . On the contrary, for hot‐carrier solar cells in which the kinetic energy of carriers is extracted to become output electrical power, the carrier temperature becomes the main focus; hence, intraband carrier‐carrier scattering is crucial and cannot be ignored.…”

“…However, a recent theoretical study has suggested that carrier temperatures can be significantly higher than the lattice temperatures in conventional solar cells, especially when photovoltaic devices operate near a short-circuit condition. 14 On the contrary, for hot-carrier solar cells [15][16][17][18][19][20][21][22][23][24] in which the kinetic energy of carriers is extracted to become output electrical power, the carrier temperature becomes the main focus [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] ; hence, intraband carrier-carrier scattering is crucial and cannot be ignored.…”

Electron extraction from excited quantum dots with higher order coulomb scattering

“…A big contribution to conversion loss in a hot-carrier solar cell is the thermalisation between the hot electron and the lattice. Thus, it is an objective to increase the thermalisation time in the cell [16][17][18][19]. Further, it has been argued that the hotcarrier cooling rate can be slowed down by a combination of phonon bottleneck [20] and reduced accessibility of the phase space by employing nanostructures like quantum wells or quantum dots (QDs) rather than their bulk counterpart [21][22][23][24][25].…”