Tailoring Mid-IR emissivity in zinc-phatolcyanine doped PMMA films for efficient day and night radiative cooling

We report on the fabrication and optical characterization of free-standing polymeric films composed of polymethyl methacrylate (PMMA) doped with various concentrations of substituted zinc phthalocyanine. We utilized a Zn phthalocyanine functionalized to prevent aggregation and improve solubility. Specifically, the Zn phthalocyanine is functionalized with four tert-butyl groups (-R) at the β-positions, resulting in Zn-Pc-R. The optical properties of free-standing polymeric films were investigated across the visible to mid-infrared spectral ranges (0.4–25 μm) to evaluate their potential for radiative cooling applications. Transmittance and reflectance spectra were measured via FTIR spectroscopy and used to calculate spectral emissivity. The results show that Zn-Pc-R concentration significantly influences IR absorption and emissivity, particularly within the atmospheric transparency windows. A radiative cooling quality factor was defined to assess the films’ performance by combining IR emissivity and solar-weighted absorption. The optimized formulation shows promise for both daytime and nighttime radiative cooling, suggesting that zinc phthalocyanine dispersed in a polymethyl methacrylate matrix (Zn-Pc-R/PMMA) can serve as a flexible, scalable platform for passive thermal management technologies.