Assessing the Efficiency of Advanced Multijunction Solar Cells in Real Working Conditions: A Theoretical Analysis

Multijunction (MJ) solar cells are currently seen as one of the most promising options toward achieving solar energy to electricity conversion efficiencies exceeding 50%. The detailed balance theory provides a practical tool for tailoring MJ solar cells, taking several strong assumptions regarding the spectral input or the cell temperature. However, solar cells in real working operation may meet conditions that differ significantly from the ideal conditions for which they were designed. Assessing the extent to which advanced MJ solar cell architectures are able to withstand changes in the operating conditions is thus crucial toward ensuring an efficient use of MJ solar cells in real working operation. In this paper, the sensitivity of current-constrained MJ solar cells to operating conditions was studied by quantifying the decrease in the conversion efficiency associated with a change in the spectral input, the illumination level, and the cell working temperature. The sensitivity of MJ solar cells to the spectral content of the light was shown to be significant for cell architecture involving four subcells and more. On the contrary, the gain in efficiency achieved by tailoring the combination of bandgap to a specific value of the working temperature or the illumination level was demonstrated to be low. The implications for future generations of MJ solar cells comprising up to ten subcells are also addressed.