Enhanced Chlorophyll A Purification and Dye Sensitized Solar Cell Performance
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Enhanced Chlorophyll A Purification and Dye Sensitized Solar Cell Performance Komal Magsi1,2, Ping Lee1,2, Yeona Kang1, Soumya Bhattacharya1, Charles M Fortmann1,2 1
Materials Science Department, Stony Brook University, Stony Brook, NY, 11790, U.S.A. 2
Idalia Solar Technologies, 270 Lafayette St. Suite 1402 New York, NY, 10012, U.S.A.
ABSTRACT Dye-sensitized solar cells (DSSC) may provide an economical alternative to the present p–n junction photovoltaic devices. Here the relation between chlorophyll purity and photovoltaic performance was examined. Also the commercial grade copper chlorophyll was examined. The performance under simulated sunlight and the quantum efficiency were measured. All samples had large short wavelength quantum efficiency however the high purity chlorophyll had larger quantum efficiency in the visible. The highest purity samples produced DSSC solar cells with the highest open circuit voltage and efficiency while the fill factor and the short circuit current were not strongly correlated with purity. The un-altered short circuit current suggests that chlorophyll attachment and charge transfer at the titanium oxide are not altered by impurities. However the results suggest that impurities (and/or copper in the commercial chlorophyll case) alter the photo-absorption and the electrolyte so as to either change the iodine chemical potential or decrease the diffusivity of iodine ions. INTRODUCTION The amount of sunlight hitting earth in one hour exceeds what all 6.8 billion humans could consume in an entire year. [1] Solar scientists have been intrigued by the idea of harnessing the suns energy for many years. It has been shown that distinct chemical reactions occur when certain materials are exposed to sunlight. Recently, there has been great interest in the natural process known as photosynthesis, whereby plants use sunlight to split water into its components H2 and O2 and subsequently convert atmospheric CO2 to carbohydrates. [2] 6CO2 + 6H2O (+sunlight) à C6H12O6 + 6O2 Photosynthesis is a remarkable process that occurs in plant chloroplasts using chlorophyll, the pigments of photosynthesis first described by Pelletier and Caventou. [2] Where chlorophyll directly absorbs incident photons as well as generating and transferring photo-excited electrons. In plants the process results in chemical reactions including the splitting of water molecules and the resultant generation of sugars. Graetzel and Kay established that chlorophyll could be used in a DSSC albeit with conversion efficiencies far below that of best dyes and far below that of traditional semiconductor based photovoltaic solar cells. [3] The molecular structure of chlorophylls a and b consists of a ring-like structure, the porphyrin ring, and a long organic phytol tail. The porphyrin ring is a stable ring-shaped molecule around which electrons move freely. In natural chlorophyll a magnesium atom is positioned at the center of the porphyrin ring as seen in Fig. 1. In the case of copper chlorophyll a copper atom
replaces the magnesium
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