Liquid‐Based Multijunction Molecular Solar Thermal Energy Collection Device

Photoswitchable molecules‐based solar thermal energy storage system (MOST) can potentially be a route to store solar energy for future use. Herein, the use of a multijunction MOST device that combines various photoswitches with different onsets of absorption to push the efficiency limit on solar energy collection and storage is explored. With a parametric model calculation, it is shown that the efficiency limit of MOST concept can be improved from 13.0% to 18.2% with a double‐junction system and to 20.5% with a triple‐junction system containing ideal, red‐shifted MOST candidates. As a proof‐of‐concept, the use of a three‐layered MOST device is experimentally demonstrated. The device uses different photoswitches including a norbornadiene derivative, a dihydroazulene derivative, and an azobenzene derivative in liquid state with different MOSTproperties, to increase the energy capture and storage behavior. This conceptional device introduces a new way of thinking and designing optimal molecular candidates for MOST, as much improvement can be made by tailoring molecules to efficiently store solar energy at specific wavelengths. Molecular photoswitches can store solar energy by photochemical conversions. This article investigates theoretically what happens to the solar energy capture efficiency if multiple molecular systems optimized for different parts of the solar spectrum are combined. Further, an experimental device that combines three different molecular photoswitches illustrates the concept.