Скачать или смотреть Role and optimization of diffraction grating for light trapping in ultrathin solar cells - SPIE 2022

Ultrathin solar cells (UTSC) are a realistic way to achieve low-cost high efficiency photovoltaic (PV) devices. Beyond reducing material costs, these devices offer several advantages, such as flexibility, low weight and endurance to harsh environments, attending applications such as agro-PV, vehicle integrated-PV and spatial-PV. One of the most used strategies for light trapping in UTSC is the use of subwavelength diffraction gratings to scatter and couple light to resonant modes. In this work, we present a thorough study on the role and the optimization of back diffraction gratings used for light reflection and scattering in GaAs UTSC. We follow two complementary paths in the search for the optimum parameters: a meta-heuristic method (genetic algorithm) and an approach based on the physical understanding of the system. With the latter, we study the influence of parameter variations for the grating (period and thickness) and for the pattern (fill factor and shape) on the diffraction efficiencies. This allows us to optimize the energy distribution at specific diffraction orders, resulting in optimized coupling to guided modes and a stronger multiresonant absorption. Guided by this approach, we show a total absorption of 92.5% of the solar photons above the bandgap for a 100 nm-thick GaAs absorber. After accounting for parasitic absorption, the estimated short-circuit current of this device is 27.0 mA/cm2, significantly beyond the current state-of-the-art for similar thicknesses. We will also discuss routes towards even higher currents by using non-symmetric structures to break the degeneracy of resonant modes.