Dye Sensitized Solar Cells - Working Principles, Challenges and Opportunities

Even before the industrial revolutions human life quality is greatly affected by the availability of energy. The escalated and savage consumption of conventional sources of energy are leading to forecasted energy and environmental crises. Renewable energy sources such as solar energy are considered as a feasible alternative because “More energy from sunlight strikes Earth in 1 hour than all of the energy consumed by humans in an entire year.”(Lewis, 2007). Facilitating means to harvest a fraction of the solar energy reaching the Earth may solve many problems associated with both the energy and global environment (Nansen, 1995). Therefore, intensive research activities have resulted in attention-grabbing to the different classes of organic and inorganic based solar cells. A major study by IntertechPira stated that “The global Photovoltaic (PV) market, after experiencing a slow period, is expected to double within the next five years, reaching US$ 48 billion. Waferbased silicon will continue as the dominant technology, but amorphous thin-film and Cadmium Telluride (CdTe) technologies will gain ground, and are expected to account for a combined 22% of the market by 2014” (www.intertechpira.com). A solar cell is a photonic device that converts photons with specific wavelengths to electricity. After Alexandre Edmond Becquerel (French physicist) discovered the photoelectrochemical (photovoltaic) effect in 1839 (Becquerel, 1839) while he was investigating the effect of light on metal electrodes immersed in electrolyte, research in this area continued and technology developed to produce many types and structures of the materials presently used in photovoltaic (PV) technology. First and second generations photovoltaic cells are mainly constructed from semiconductors including crystalline silicon, III-V compounds, cadmium telluride, and copper indium selenide/sulfide (Hara & Arakawa, 2003; Hoffert, 1998; Zhao et al., 1999). Low cost solar cells have been the subject of intensive research work for the last three decades. Amorphous semiconductors were announced as one of the most promising materials for low cost energy production. However, dye sensitized solar cells DSSCs emerged as a new class of low cost energy conversion devices with simple manufacturing procedures. General comparison between semiconductor based solar cells and dye sensitized solar cells is presented in Table 1. Incorporation of dye molecules in some wide bandgap semiconductor electrodes was a key factor in developing photoelecrochemical solar cells. Michael Gratzel and coworkers at the Ecole Polytechnique Federale de Lausanne (Gratzel, 2003; Nazerruddin et al., 1993; O' Regan & Gratzel, 1991) succeeded for the first time to produce what is known as “Gratzel Cell” or