Near-infrared absorbing squaraine dye with extended π conjugation for dye-sensitized solar cells

A NIR absorbing squaraine dye has been synthesized as a sensitizer for use in dye-sensitized solar cells (DSCs). Following computational calculations, a benz[cd]indole moiety was selected as an electron-rich heterocyclic component and condensed with indole-based emisquaraine bearing a carboxyl group, as an anchor for their immobilization on TiO2, to obtain an unsymmetrical squaraine with extended absorption due to its extensive π conjugation. The cells based on this dye exhibited a spectral response in the near-infrared region over 750 nm in addition to the visible region with a light absorption edge at 900 nm. The cells showed 1.1% efficiency and Incident Photon Current Efficiency (IPCE) of 36% at 800 nm.