Particle-engineered CaAlSiN3:Eu2+ phosphors for scattering-assisted tandem luminescent solar concentrators

Particle engineering balances the scattering-luminescence trade-off in phosphor LSCs. • Mie theory and Monte Carlo modeling reveal size-dependent photon harvesting and transport. • Ball milling tunes size and annealing mitigates defects and limits emission loss. • A 100 cm 2 tandem LSC reaches a power conversion efficiency of 2.72%. Luminescent solar concentrators (LSCs) enable large-area solar harvesting and spectral conversion, but their performance is often limited by incomplete solar spectrum utilization and optical losses. Tandem architectures can broaden spectral harvesting. In phosphor-based tandem LSCs, however, particle-level scattering governs both light harvesting and waveguiding efficiency, and the trade-off between scattering and luminescence remains unresolved. Here, we report a scattering-assisted tandem LSC enabled by particle-engineered CaAlSiN 3 :Eu 2+ (CASN) phosphors. Theoretical scattering analysis and Monte Carlo ray tracing simulations show that reducing the particle size improves both solar harvesting and photon transport. To address this trade-off, a two-step post-treatment combining ball milling and rapid thermal processing was developed, in which thermal annealing mitigates milling-induced surface defects and largely preserves luminescence efficiency. The optimized single-layer LSC exhibits an increase in short-circuit current density from 1.48 to 1.99 mA/cm 2 and a power conversion efficiency of 1.56%. When integrated beneath a tetra(t-butyl)rubrene-based top layer, the scattering-assisted tandem LSC achieves a power conversion efficiency of 2.72%. These results establish CASN as a robust luminophore for tandem LSCs, show that powder-level characteristics strongly influence device performance, and offer a general particle engineering route toward high-efficiency scattering-assisted LSCs. Download: Download high-res image (177KB) Download: Download full-size image Particle-engineered CaAlSiN 3 :Eu 2+ phosphors enable a scattering-assisted tandem luminescent solar concentrator with enhanced solar harvesting and photon transport. Ball milling combined with rapid thermal processing preserves strong luminescence while optimizing particle scattering, leading to high external optical efficiency and tandem efficiency in a tandem device integrating tetra-tert-butylrubrene and CaAlSiN 3 :Eu 2+ phosphors.