Dextran-templating hydrothermal synthesis of monoclinic WO3 exhibits excellent specific surface area of similar to 110 m(2)/g and a monomodal pore distribution with an average pore diameter of similar to 20 nm. Dextran plays a crucial role in generating porosity on WO3. The role of supporting dextran has been investigated and found to be crucial to tune the surface area, porosity, and morphology. The photoluminescence and X-ray photoelectron spectroscopy studies reveal the existence of oxygen vacancies in substoichiometric WO3, which creates localized defect states in WO3 as synthesized through this templating method. The highly mesoporous WO3 has been further explored as an interfacial cathode buffer layer (CBL) in dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). A significantly enhanced photoconversion efficiency has boosted up the performance of the counter electrode used in traditional DSSC (as platinum) and PSC (as carbon) devices by similar to 48 and similar to 29%, respectively. The electrochemical impedance and incident photon to current conversion efficiency (IPCE) studies were also analyzed in order to understand the catalytic behavior of the WO3 interfacial CBL for both DSSCs and PSCs, respectively. The much higher surface area of WO3 enables rapid electron hopping mechanism, which further benefits for higher electron mobility, resulting in higher short circuit current. Through this study, we were able to unequivocally establish the importance of buffer layer incorporation, which can further help to integrate the DSSC and PSC devices toward more stable, reliable, and enhanced efficiency-generating devices. In spite of this, using WO3 constitutes an important step toward the efficiency improvement of the devices for futuristic photoelectrochromic or self-powered switchable glazing for low-energy adaptive building integration.