Photochromic dye-sensitized solar cells with light-driven adjustable optical transmission and power conversion efficiency

Semi-transparent photovoltaics only allow for the fabrication of solar cells with an optical transmission that is fixed during their manufacturing resulting in a trade-off between transparency and efficiency. For the integration of semi-transparent devices in buildings, ideally solar cells should generate electricity while offering the comfort for users to self-adjust their light transmission with the intensity of the daylight. Here we report photochromic dye-sensitized solar cells (DSSCs) based on dyes with a donor-π-conjugated-bridge-acceptor structure where the π-conjugated bridge is substituted by a diphenyl-naphthopyran photochromic unit. DSSCs show change in colour and self-adjustable light transmittance when irradiated and demonstrate a power conversion efficiency up to 4.17%. The colouration–decolouration process is reversible and these DSSCs are stable over 50 days. We also report semi-transparent photo-chromo-voltaic mini-modules (active area of 14 cm²) exhibiting a maximum power output of 32.5 mW after colouration.