Smart windows are currently under intense investigation and thorough optimization in order to be effectively implemented in modern energy-saving buildings. The possibility of altering the light transmission properties of a window upon a voltage-, light-, or heat-induced external stimulus is a fundamental requirement to be pursued, and scientists are carefully investigating the quality, speed, and repeatability of the optical switching phenomenon. The resulting smart windows (often referred to as “building shells”) offer several advantages if compared to traditional ones, with a neat money saving for air-conditioning, heating, lighting, and curtains. A new photoelectrochromic device (PECD) is presented in this work proposing the combination of a WO3-based electrochromic device (ECD) and a polymer-based dye-sensitized solar cell (DSSC). In the newly designed architecture, a photocurable polymeric membrane is employed as quasi-solid electrolyte for both the ECD and the DSSC. In addition, a photocurable fluoropolymeric system is incorporated as solution-processable external protective thin coating film with easy-cleaning and UV-shielding functionalities. Such new polymer-based device assembly is characterized by excellent device operation with improved photocoloration efficiency and switching ability compared with analogous PECDs based on standard liquid electrolyte systems. In addition, long-term (>2100 h) stability tests under continuous exposure to real outdoor conditions reveal the remarkable performance stability of this new quasi-solid PECD system, attributed to the protective action of the photocurable fluorinated coating that effectively prevents photochemical and physical degradation of the PECD components during operation. This first example of quasi-solid PECD system paves the way for a new generation of thermally, electrochemically, and photochemically stable polymer-based PECDs, and provides for the first time a clear demonstration of their true potential as readily upscalable smart window components for energy-saving buildings.