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

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.