Regenerative solar cells conversion efficiencies

Dye sensitization of electrodes is an old area of science with a rich history. The field has experienced renewed interest owing to the development of high surface area colloidal semiconductor electrodes. These materials yield impressive solar conversion efficiencies when employed in regenerative solar cells that have already found niche applications and have the real possibility of replacing traditional solid-state photovoltaics. Thus for the first time in history a solar cell designed to operate on a molecular level is useful from a practical point of view. It is also likely that other applications in the growing areas of molecular photonic materials will arise. 

Table 1.1 Maximum-power conversion efficiency of selected regenerative solar cells...

It has been illustrated that polycrystalline materials can be operated in regenerative electrolytic solar cells yielding substantial fractions of the respectable energy conversion efficiency obtained by using single crystals. Pressure-sintered electrodes of CdSe subsequently doped with Cd vapor have presented solar conversion efficiencies approaching 3/4 of those exhibited by single-crystal CdSe electrodes in alkaline polysulfide PEC [84]. 

Fig. 5.65 Dependence of the solar conversion efficiency (CE) on the threshold wavelength (Ag) for a quantum converter at AM 1.2. Curve 1 Fraction of the total solar power convertible by an ideal equilibrium converter with no thermodynamic and kinetic losses. Curve 2 As 1 but the inherent thermodynamic losses (detailed balance and entropy production) are considered. Continuous line Efficiency of a regenerative photovoltaic cell, where the thermodynamic and kinetic losses are considered. The values of Ag for some semiconductors are also shown (according to J. R. Bolton et al.)... 

The theoretical solar conversion efficiency of a regenerative photovoltaic cell with a semiconductor photoelectrode therefore depends on the model used to describe the thermodynamic and kinetic energy losses. The CE values, which consider all the mentioned losses can generally only be estimated the full line in Fig. 5.65 represents such an approximation. Unfortunately, the materials possessing nearly the optimum absorption properties (Si, InP, and GaAs) are handicapped by their photocorrosion sensitivity and high price. 

Maximum energy conversion efficiencies of (/ lax = 0.1086 have recently been measured and verified for dye-sensitized regenerative cells illuminated with air mass 1.5 simulated solar irradiation [27]. The efficiency of photoelectrosynthetic cells must also include contributions from the free energy stored in the chemical products of the reduction and oxidation reactions. 

In 1976, the first regenerative PECs with substantial and sustained solar to electrical conversion efficiency were demonstrated. These PECs are based on n-type cadmium chalcogenide (S, Se or Te) electrodes immersed in aqueous polychalcogenide electrolytes. The cells were introduced by Hodes, Cahen, and Manassen (31), Wrighton and coworkers [32], and Heller and Miller [33] and were capable of converting up to 7% of insolation to electrical energy. Most investigations of these systems focused on solid-state and interfacial aspects of these PECs and photodriven oxidation of polysulfide at the photoelectrode was represented ... 

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