High conversion efficiency photoelectrochemical solar cells

The present review focusses on the prospectives and perspectives of high conversion efficiency photoelectrochemical (PEG) solar cells. The PEC solar cells score over their solid state counterparts on several points. Some of these are ease of fabrication and inbuilt storage capability. In order to make PEC solar cells viable, their conversion efficiencies need to be enhanced so as to reach optimum values. Several feasible efficiency enhancement processes for PEC cells such as electrode surface modification, photoetching, electrolyte modification etc. have been described and discussed in this article. The case of efficiency enhancement of n-GaAs based PEC solar cell through the modification of GaAs by Os3+ or Ru3+ ions leading to efficiency enhancement from 9 to 15% has been described and discussed. In regard to efficiency enhancement through electrolyte modification, the example of n-CdSe based PEC cell where the electrolyte (K-3 Fe(CN)(6) / K-4 Fe(CN)(6)) is modified through KCN has been dealt with. The efficiency obtained in this cell is upto similar to 16%. For the PEC solar cells embodying the d-d phototransition, MX(2) type layered materials, the most dramatic conversion efficiency enhancements come through photoetching of electrode surfaces. We have described and discussed in detail the efficiency enhancements in n-WSe2 / I-3(-) I-/Pt solar cells through photoetching of n-WSe2 photoelectrodes in 0.1 M aquaregia. High efficiencies upto similar to 17% have been obtained for those solar cells. Yet another route of fabricating viable PEC solar cells giving high power output corresponds to the development of newer PEC cell designs. One example of the newer cell designs which has been described and discussed in this article corresponds to semiconductor-septum (SC-SEP) PEC solar cell. The SC-SEP, PEC solar cells have been found to yield higher power outputs (V-oc and I-sc) than the conventional single compartment PEC cells. For example, n-CdSe/Ti septum based PEC solar cell with configuration - Pt, 1 M-3S//n-CdSe/Ti/0.1M AgNO3, Pt has been found to give higher power output (1.42 V and 20 mA/cm(2)), as compared to n-CdSe based conventional PEC cell (0.64 V and 6 mA/cm(2)). Similarly, n-TiO2/Ti septum electrode based SC-SEP, cell - Pt, 1 M NaOH/n-TiO2/Ti/0.1M AgNO3, Pt also gives higher power output (1.2 V and 15 mA/cm(2)). The case of another new PEC cell design incorporating nanostructured TiO2 photoelectrode overlaid with special dye (Ruthenium trinuclear cyanide complex) and exhibiting efficiencies of 7% (under usual solar illumination) and 12% (in diffuse solar light) has also been outlined.