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Dye-sensitized solar cells (DSSCs) have aroused great interest and been regarded as a potential renewable energy resource among the third-generation solar cell technologies to fulfill the 21 century global energy demand. DSSCs have notable advantages such as low cost, easy fabrication process and being eco-friendly in nature. The progress of DSSCs over the last 20 years has been nearly constant due to some limitations, like poor long-term stability, narrow absorption spectrum, charge carrier transportation and collection losses and poor charge transfer mechanism for regeneration of dye molecules. The main challenge for the scientific community is to improve the performance of DSSCs by using different approaches, like finding new electrode materials with suitable nanoarchitectures, dyes in composition with promising semiconductors and metal quantum dot fluorescent dyes, and cost-effective hole transporting materials (HTMs). This review focuses on DSSC photo-physics, which includes charge separation, effective transportation, collection and recombination processes. Different nanostructured materials, including metal oxides, oxide perovskites and carbon-based composites, have been studied for photoanodes, and counter electrodes, which are crucial to achieve DSSC devices with higher efficiency and better stability.

Polyaniline (PANI) and silver doped polyaniline (Ag/PANI) thin films were deposited on stainless steel substrates by a dip coating technique. To study the effect of doping concentration of Ag on the specific capacitance of PANI the concentration of Ag was varied from 0.3 to 1.2 weight percent. Fourier transform-infrared and Fourier transform-Raman spectroscopy, and energy dispersion X-ray techniques were used for the phase identification and determination of the doping content in the PANI films, respectively. The surface morphology of the films was examined by Field Emission Scanning Electron Microscopy, which revealed a nanofiber like structure for PANI and nanofibers with bright spots of Ag particles for the Ag/PANI films. There was decrease in the room temperature electrical resistivity of the Ag/PANI films of the order of 10(2) with increasing Ag concentration. The supercapacitive behavior of the electrodes was tested in a three electrode system using 1.0 M H(2)SO(4) electrolyte. The specific capacitance increased from 285 F g(-1) (for PANI) to 512 F g(-1) for Ag/PANI at 0.9 weight percent doping of Ag, owing to the synergic effect of PANI and silver nanoparticles. This work demonstrates a simple strategy of improving the specific capacitance of polymer electrodes and may also be easily adopted for other dopants.

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Undoped and Mn doped Polyaniline (PANI) thin films were deposited on stainless steel substrates by sonochemical method. Films deposition was done using dip coating technique. To study the Mn doping effect on the specific capacitance of PANI, concentration of Mn was varied from 0.4 to 1.6 wt %. The Fourier Transform-IR (FT-IR) and Raman spectroscopy techniques have been used for the phase identification and determination of the Mn in the PANI films. Surface morphology was examined by using Field Emission Scanning Electron Microscopy (FESEM) which showed nanofiber aggregate structure of undoped PANI and porous and well distributed nanofibers for the doped PANI. The supercapacitive behavior of the electrodes was tested in three electrode system with 1.0 M H 2 SO 4 electrolyte by using cyclic voltammetry. The specific capacitance value increases from 285 to 474 F g À1 as the Mn concentration was increased. This work demonstrates a simple strategy of improving specific capacitance of the polymer and hence may be adopted easily for other dopants also. Thus the work will open a new avenue for designing low cost high performance devices for better supercapcitors.

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