Trifunctional Liquid Optical Spacer for Luminescent Solar Concentrators: Selective Photon Recycling, Reabsorption Suppression, and Self-Powered Privacy Monitoring.

Luminescent solar concentrators (LSCs) are promising large-area photon-harvesting devices for building-integrated photovoltaics, yet their performance is limited by insufficient solar absorption and severe photoluminescence reabsorption at high luminophore loadings. Here, liquid optical spacer LSCs (LOS-LSCs) with wavelength-selective scattering synergistically mitigate both challenges. A colloidal CsPbCl3:Yb3+ nanocrystal-loaded spacer is inserted into bilayer LSCs. These nanocrystals selectively redirect otherwise transmitted short-wavelength photons back into LSCs via Rayleigh scattering, achieving selective photon recycling. Concurrently, the LOS reduces total internal reflection events, mitigating reabsorption loss caused by photoluminescence penetration through luminescent layers. The absorption efficiency improves from 7.7% to 16.0% (a relative improvement of 108%), while edge-emission efficiency remains at the theoretical limit, yielding a competitive external optical efficiency of 9.9% and a power conversion efficiency of 1.60%. Moreover, the near-infrared-emitting LOS also enables LOS-LSCs to function as self-powered privacy monitors, highlighting their potential for multifunctional and intelligent building-integrated photovoltaics.