Nonequilibrium Fluctuations and Intrinsic Stability of Nanostructured Solar Cells: Microscopic Derivation and Universal Laws

Abstract

We study nonequilibrium fluctuations of efficiency in nanostructured solar cells. Our contribution is threefold. First, we derive a microscopic stochastic model of efficiency from a two-state master equation describing absorption, radiative recombination, and extraction. This derivation establishes an explicit link between efficiency fluctuations and entropy production, and justifies the thermodynamic affinity through local detailed balance. Second, we review universal fluctuation laws established in the recent literature and apply them for the first time to the real parameters of nanostructured solar cells. We show that the total entropy production behaves as a submartingale, and that its negative exponential is a martingale. For a biased discrete random walk, the exact infimum law is verified numerically in the near-equilibrium regime, then applied to realistic solar cell configurations. Third, our simulations show that nanostructured solar cells operate in a strongly nonequilibrium regime, where negative entropy fluctuations, and hence efficiency fluctuations, are exponentially rare. Over all simulated trajectories, most configurations show no detectable negative fluctuation, consistent with the theoretical prediction. These results explain the intrinsic statistical stability of the devices and provide a conceptual and quantitative framework for understanding efficiency fluctuations around the mean values. They do not modify the mean efficiencies obtained previously, but clarify their statistical robustness in the strongly nonequilibrium regime.