HIGH CONVERSION EFFICIENCY PHOTOELECTROCHEMICAL SOLAR-CELLS

The present review focusses on the prospectives and perspectives of hi gh conversion efficiency photoelectrochemical (PEG) solar cells. The P EC solar cells score over their solid state counterparts on several po ints. Some of these are ease of fabrication and inbuilt storage capabi lity. In order to make PEC solar cells viable, their conversion effici encies need to be enhanced so as to reach optimum values. Several feas ible 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 enhance ment 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 modifie d through KCN has been dealt with. The efficiency obtained in this cel l is upto similar to 16%. For the PEC solar cells embodying the d-d ph ototransition, MX(2) type layered materials, the most dramatic convers ion efficiency enhancements come through photoetching of electrode sur faces. We have described and discussed in detail the efficiency enhanc ements in n-WSe2 / I-3(-) I-/Pt solar cells through photoetching of n- WSe2 photoelectrodes in 0.1 M aquaregia. High efficiencies upto simila r to 17% have been obtained for those solar cells. Yet another route o f fabricating viable PEC solar cells giving high power output correspo nds to the development of newer PEC cell designs. One example of the n ewer cell designs which has been described and discussed in this artic le 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 conventi onal PEC cell (0.64 V and 6 mA/cm(2)). Similarly, n-TiO2/Ti septum ele ctrode 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 anothe r 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.