Modeling the efficiency of multijunction solar cells

The efficiency of multijunction solar cells (MSCs) $\eta$ is calculated taking into account radiative recombination, Shockley-Read recombination, front and rear surface recombination, recombination in the space-charge regions, and recombination at heterojunctions. Calculation is performed by self-consistent solution of the photocurrent, photovoltage, and heat-balance equations. MSC cooling by increasing the numbers of cells $n$ and improvement in the conditions of heat removal is taken into account. An effect leading to a decrease in the photocurrent with increasing $n$, associated with narrowing of the energy ranges of photons incident on the MSC cell, is considered. It is found that a significant increase in the MSC efficiency can be achieved by improving the heat-removal conditions, in particular, through the use of radiators and increasing the MSC grayness factor to unity. The results obtained are compared to those of other authors. It is shown that the calculated dependences $\eta(n)$ are in agreement with experimental values.