Effects of spatio-temporal variations of solar light on the multiscale optical and electrical characteristics of ultrathin tandem solar cells

Ultrathin tandem solar cells have potential for a wide range of applications due to flexibility, high power-to-weight ratio, price competitiveness (low-cost and low capex). However, unlike standard tests under air-mass1.5 (AM1.5) 1 sun illumination, differences in spectral irradiance and incidence angle caused by spatio-temporal variation of solar light have significant effects on the tandem solar cells, especially on the ultrathin tandem solar cells, which are much more sensitive to incidence angle due to the sub-micro/micro textured structures. We develop a multiscale optical model and photovoltaic characteristic model for detailed description of photon propagation and carrier transport in the ultrathin tandem solar cells, respectively. Though analyses on the effect of inverted pyramid photonic crystal architecture on light absorption of the ultrathin tandem solar cells, the optimal structural parameters of inverted pyramid photonic crystal architecture are obtained, which leads to an improvement of the power conversion efficiency of ultrathin tandem solar cell by 0.82 % compared to the tandem solar cells with pristine thickness (∼180 μm). Based on the optimized ultrathin tandem solar cells, detailed mechanisms of the effects of variation in regional and daily spectral irradiances on the PV characteristics are unravelled. Compared to daily spectral irradiance variations, regional spectral irradiance variations have a greater effect on the structural dimensions and performance of ultrathin tandem solar cells. However, in the daily solar light variations, incidence angle variation has a significant effect on ultrathin tandem solar cells, and this effect is primarily reflected in the bottom sub-cells. The unravelled mechanism of the effect of incidence angle variation helps us propose a recommendation to improve the daily output power of the ultrathin tandem solar cells (2312.30 W·h/m²) in the analyses under real-world condition.