Tuning Radiative Properties of Multiscale Porous Transparent Silica Aerogels for Efficient Solar Interfacial Evaporation

High-efficiency multistage solar interfacial evaporation requires covers that maximize solar spectrum transmission to the absorber while limiting thermal losses. Here, we establish a coupled numerical and experimental framework to tune the optical properties of transparent silica aerogels.We identify wavelengths < 500 nm as a critical, morphology-tunable scattering regime that also coincides with the AM 1.5G peak. Design maps suggest an optimal design in which  a mean particle radius < 4 nm and a bulk density < 200 kg m −3 deliver total transmittance > 95% with haze < 5%. Further promotion in forward scattering can boost the transmittance even when haze is relatively high. Experimentally, guided by the multiscale model, we tuned the sol-gel process to reduce the silica aerogel mean scattering center radius from 4.9 to 3.1 nm, yielding a 5 mm-thick sample with a solar-weighted transmittance of 95.2%. Integrated as a greenhouse-selective cover in a 10-stage solar evaporation device, the optimized silica aerogel boosts the water production rate by 19.3%, from 5.22 to 6.23 kg m −2 h −1 , demonstrating that morphology tuning translates into system-level performance gains. These results provide actionable design rules and a validated predictive modeling framework for low-haze and high-transparency aerogel covers that enable efficient solar evaporation.