Radiative coupling the easy way: Using transfer coefficients to model series-connected multi-junction solar cells

TL;DR

This paper introduces a simplified model using transfer coefficients to account for radiative coupling in series-connected multi-junction solar cells, enabling easier calculation of device characteristics and efficiency optimization.

Contribution

It presents a novel transfer coefficient approach to model radiative exchange in multi-junction solar cells, simplifying analysis and efficiency prediction.

Findings

Transfer coefficients effectively model radiative coupling.

The model allows straightforward calculation of short circuit current.

Efficiency peaks can be predicted under standard illumination.

Abstract

When the quality of multijunction solar cells becomes sufficiently high, radiative exchange of photons between cells has to be taken into account to properly model these devices. In this work it is shown how this radiative coupling can be accounted for in series connected multi-junction solar cells by constants called transfer coefficients. Under the assumption that the exchanged radiation only travels one way, from higher to lower band gaps, the transfer coefficients allows the relation between the voltage and current of the device to be expressed by a convenient mathematical expression. Another advantage of this model is that it allows the short circuit current of radiatively coupled multijunction cells to be calculated in a straightforward way. Non-ideality may be included by means of the external radiative efficiency. A number of examples are discussed to show how the transfer coefficients describes the radiative coupling. In addition, the model is used to find the efficiency peaks of radiatively coupled multi-junction cells when illuminated by the AM1.5 spectrum.