Sensitization effect in conducting polyaniline by rhodamine 6G

Rhodamine 6G (R6G), an n-type dye, has been employed at small concentrations (0–15 mM/monomer) for sensitizing conducting polyaniline (PANI) in solid-state photocells with the configuration Au/PANI/SPE+R6G/ITO. It is observed that a p–n junction is formed at the PANI/dye interface. The photosensitivity factor (S) is observed to be maximum at a dye concentration of 6.3 mM/monomer. The variation of the dark (I_d) and light (I_l) current with respect to the dye concentration in the linear portion of the current–voltage (I–V) characteristic reveals that light current goes through a maximum whereas dark current remains more or less constant. Thus, it is the variation of the light current (I_l) that is more important and is one of the reasons for maximum photosensitivity at a certain dye concentration. The mechanism of the dye-sensitization process is explained on the basis of the energy band diagram of the materials forming the photocell. The observed photosensitivity is due to the lowering of the potential barrier in the presence of light at the PANI/dye interface.