Thermodynamics of Photon Management in Solar Cells

Abstract: In obtaining a high efficiency solar cell device, proper management of the flow of light needs to be ensured. There are currently many theories that have been developed to estimate the enhancement limit of various photon management strategies on the different solar cell parameters (short circuit current, open-circuit voltage, efficiency). In particular, thermodynamic theories of the photon management have been shown to be a useful tool to estimate the impact of different light management strategies used for a solar cell.

In this thesis work, we developed an analytical formalism of thermodynamics of photon management in solar cells that considers realistic absorption characteristics. We utilize the formalism to deduce the impact of photon management strategies in enhancing open-circuit voltage. Two idealized absorption responses are utilized as a reference: the double pass Beer-Lambert with perfect light incoupling and the Lambertian case. The Beer-Lambert response is given to present the case of perfect anti-reflection without additional light trapping while the Lambertian case is given to represent the case of optimum light trapping. Exploiting our formalism we examine the impact of Photon recycling for different cases of interest. First, in the radiative limit where thermodynamic losses such as parasitic re-absorption and non-radiative recombination can be ignored. Second, Photon recycling in the presence of non-radiative recombination loss and parasitic re-absorption losses.

In addition, we developed an analytical formalism of the thermodynamics of photon management in four terminal tandem solar cells. We examined in greater detail the impact of various absorption response assumptions on the device performance. We explored in depth the influence of photon recycling, whether through re-absorption of re-emitted photons in the top cell, which mainly impact the top cell open-circuit voltage or through luminescence coupling with the bottom cell, which additionally contribute to the bottom cell short circuit current. We particularly focused on the case of tandem organo-metal halide perovskite/c-Si cells. We identified important range of substrate/cladding refractive index and parasitic photon re-absorption probability in the top cell in which the effects of photon recycling is significant.