High‐Efficiency Structural Coloration Enabled by Defect‐Free Block Copolymer Self‐Assembly for a Solar Cell Distributed Bragg Reflector

Abstract Solar cell coloration with minimum optical loss is increasingly required for building‐integrated photovoltaics (BIPV) in modern urban areas because of its importance in harmonizing the exterior of zero‐energy buildings and surroundings. A simple strategy for developing a distributed Bragg reflector (DBR) is designated with 1D lamella‐forming polystyrene‐ b ‐poly(2‐vinylpyridine) (PS‐ b ‐P2VP) films. An optimized thermal annealing process produces defect‐free lamellar microdomains oriented parallel to the substrate throughout the film. The selective crosslinking in the P2VP block and swelling of these films in a methanol solution with methanesulfonic acid facilitate the formation of highly asymmetric gigantic lamellae, enabling the entire visible‐wavelength spectrum of DBR structural colors. Three representative red (R), green (G), and blue (B) DBR films are produced on a Si solar cell. Coloration from high‐reflectance and narrow‐width DBR films results in vividly colored Si solar cells with a minor or negligible reduction in power conversion efficiency. The approach for photovoltaics, in terms of both the attractive esthetic and technical aspects of BIPV application, offers a viable method for fabricating high‐performance DBR films based on block copolymer self‐assembly.