Reduced charge recombination by the formation of an interlayer using a novel dendron coadsorbent in solid-state dye-sensitized solar cells

3,4,5-Tris(dodecyloxy) benzoic acid (DOBA) and the Z907 dye were coadsorbed to form a light-sensitizing monolayer in a solid-state dye-sensitized solar cell (sDSC). Coadsorption of DOBA which has three hydrocarbon chains permitted preparation of a denser monolayer of dyes and DOBA. This dense monolayer formed interlayer between TiO2 and Spiro-OMeTAD (hole conductor), effectively preventing charge recombination, while half of the photocurrent was dissipated via recombination reaction when Z907 solely anchored on the surface of TiO2. Moreover, the DOBA induced a lower population of density-of-state (DOS) in the surface of TiO2, shifting the position of the conduction band (CB) toward negative values. This resulted in higher open-circuit voltage (V-OC) for the device made with Z907 and DOBA than that of the Z907-sensitized device. These surface properties were investigated using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent/photovoltage spectroscopy (IMPS and IMVS).