Kim, Beom-Su Kim, Jae-Hyun Kang, Gumin Ko, Hyungduk Gan, Qiaoqiang Kim, Sun-Kyung 2025-07-18T07:30:20Z 2025-07-18T07:30:20Z 2025-07-18 2025-05 https://pubs.kist.re.kr/handle/201004/152796 Adaptive thermal regulation is crucial for year-round energy savings in buildings, especially in mid-latitude regions. Here, leveraging the seasonally varying angles of direct sunlight, we report a microprism-array sheet that enables seasonal energy saving windows. Guided by geometric optics, the asymmetric microprismarray sheet, featuring a silver coating on the sky-facing facets, exhibited an average transmittance of 10% in summer and 53% in winter at predominant sunlight angles, compared to 30% and 38% of a standard tint film, respectively. During outdoor testing in South Korea (37 degrees N), a south-facing window integrated with the microprism-array sheet reduced floor temperatures by up to 5 degrees C during direct sunlight hours, relative to a tinted window. Notably, in east-facing windows, the microprism-array sheet transitioned from heating to cooling around 9:00 a.m., highlighting its potential for modulating seasonal thermal management. English CELL PRESS All-optical seasonal energy saving windows Article 10.1016/j.isci.2025.112514 1 iScience, v.28, no.5 iScience 28 5 Y scie scopus 001510719300001 Multidisciplinary Sciences Science & Technology - Other Topics Article THERMOCHROMIC VO2 SOLAR MODULATION SMART TEMPERATURE NANOCOMPOSITE TRANSITION HYDROGEL OXIDES FILM