Abstract
We present a novel theoretical approach to the problem of light energy conversion in thermostated semiconductor junctions. Using the classical model of a two-level atom, we deduced formulas for the spectral response and the quantum efficiency in terms of the input photons’ non-zero chemical potential. We also calculated the spectral entropy production and the global efficiency parameter in the thermodynamic limit. The heat transferred to the thermostat results in a dissipative loss that appreciably controls the spectral quantities’ behavior and, therefore, the cell’s performance. The application of the obtained formulas to data extracted from photovoltaic cells enabled us to accurately interpolate experimental data for the spectral response and the quantum efficiency of cells based on Si-, GaAs, and CdTe, among others.
Highlights
In photovoltaic cells (PVCs), light absorption promotes the transference of electrons from the valence to the conduction bands, allowing electrical energy production from light
Expression (26) indicates that the photochemical potential accounting for the unbalance induced by the light input power on the p-n junction is directly associated with the quantum efficiency of the cell, a spectral quantity that depends on the light absorption coefficient through the coefficients Bmn
The quantification of the non-equilibrium light absorption process was done through a stationary radiative current involving the difference between the input and output radiation from the cell and taking into account the crucial fact of the non-zero value of the chemical potential of photons in this non-equilibrated process
Summary
In photovoltaic cells (PVCs), light absorption promotes the transference of electrons from the valence to the conduction bands, allowing electrical energy production from light. The incoming light induces transitions of electrons from the valence to the conduction band, changing the semiconductor atoms’ energy distribution In this representation, the dynamics of a two-level atom model copes with the essential physics when explicit electron-hole recombination is neglected [3,9]. This recombination could enter our model by including non-linear terms, i.e., defining reaction constants that depend on the occupation numbers of both states This does not mean that two-level atom models lack recombination effects since transitions from the higher to the lower energy level are considered through radiative recombination, spontaneous emission, and thermal effects, all of them characterized by different rate constants. The assessment of the efficiency of the energy conversion is done by assuming a balance between absorbed and emitted radiation In this approximation, thermal interaction with the heat reservoir is not explicitly considered in the microscopic mechanism as a possible factor promoting transitions. According to Equation (4), j is proportional to the net radiation received by the semiconductor from the Sun, which promotes the transference of atoms from the ground to their excited state
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