Solid-State Photovoltaic Thin Films using TiO2, Organic Dyes, and Layer-by-Layer Polyelectrolyte Nanocomposites

We report photovoltaic devices consisting of patterned TiO2, porphyrin dyes, and layer‐by‐layer (LBL) polyelectrolyte multilayer/oligoethylene glycol dicarboxylic acid (OEGDA) composite films. A composite polyelectrolyte LBL/OEGDA film was fabricated by formation of an alternating multilayer of linear polyethyleneimine (LPEI) and polyacrylic acid (PAA), followed by immersion of the LBL film into an OEGDA aqueous solution. The ionic conductivity attained in this LBL LPEI/PAA and OEGDA composite film was approximately 10–5 S cm–1 at room temperature and humidity. Investigations of dye‐sensitized photovoltaic devices constructed with the LBL (LPEI/PAA)/OEGDA composite films, TiO2, and four types of porphyrin dyes resulted in optimization of the dye molecule and its orientation at the interface with the ionically conductive composite. The photocurrent value of photovoltaic devices constructed with the composite LBL/OEGDA film from illumination of a xenon white light source exhibited a nearly 1.5 times enhancement over the device without OEGDA. This enhancement of the photocurrent was due to the high room‐temperature ionic conductivity of the multilayer composite film. Further marked improvements of the photovoltaic performance were achieved by patterning the TiO2 electrode using polymer stamping as a template for TiO2 deposition. The device with patterned TiO2 electrodes exhibited almost 10 times larger conversion efficiencies than a similar device without patterning. Micro‐ and nanometer‐scale patterned TiO2 electrode (see Figure) and layer‐by‐layer polyelectrolyte multilayer/oligoethylene glycol dicarboxylic acid (OEGDA) composite films were applied to dye‐sensitized photovoltaic devices. Significant improvement of the photovoltaic performance was achieved by both the use of OEGDA and the patterning of the TiO2 electrode.