A New Generalized Detailed Balance Formulation to Calculate Solar Cell Efficiency Limits

Solar cells efficiency limits can be calculated either by thermodynamic or detailed balance approaches. For a single energy (i.e., single junction) solar cell, detailed balance equations are identical to the thermodynamic equations. However, standard detailed balance techniques cannot be directly used to analyze new approaches for higher efficiency solar cells if mechanisms other than radiative generation or recombination are included. A generalized form of detailed balance is presented, which is consistent with thermodynamic approaches but retains the benefits of detailed balance approaches. The generalized detailed balance is used to analyze recombination and thermalization in quantum well solar cells. This analysis demonstrates that an advantage of new approaches to high efficiency solar cells is that energy can be recovered from non-ideal or non-radiative processes and that if the solar cell system is constrained in some way, the inclusion of these non-ideal mechanisms can be beneficial.