PECS cells with solid electrolytes

A comprehensive survey of solar rechargeable PEC batteries, up to 1991, along with the historical development of photoelectrochemical cells has been given by Sharon et al. [61]. The principles and performance of solar PEC batteries with or without a membrane, with an aqueous solution or with solid-state electrolytes, are discussed there. 

In any case, it is perceived from the above discussion that the problem of longterm chemical stability of polycrystalline semiconductor liquid junction solar cells is far from being solved. Still, as already pointed out in the early research, any practical photovoltaic and PEC device would have to be based on polycrystalline photoelectrodes. Novel approaches mostly involving specially designed PEC systems with alternative solid or gel electrolytes and, most importantly, hybrid/sensitized electrodes with properties dictated by nanophase structuring - to be discussed at the end of this chapter - promise new advances in the field. 

Most detailed studies of water photodissociation on SrTi03 and Ti02 have concentrated on photoelectrochemical cells (PEC cells) operating under conditions of optimum efficiency, that is with an external potential applied between the photoanode and counterelectrode. We have become interested in understanding and improving reaction kinetics under conditions of zero applied potential. Operation at zero applied potential permits simpler electrode configurations (11) and is essential to the development of photochemistry at the gas-semiconductor interface. Reactions at the gas-sold, rather than liquid-solid, interface might permit the use of materials which photocorrode in aqueous electrolyte. 

When choosing a solar simulator for PEC research, one should carefully consider the orientation of the light exit port. Most solar simulators have their exit port oriented vertically, i.e., shining down. This is convenient for solid-state solar cells, but a bit of a hassle for PEC cells containing a liquid electrolyte -one would have to use a mirror since the photoelectrode is mounted vertically in most PEC cells. Fortunately, several manufacturers offer the possibility to have the light exit sideways. Some solar simulator manufacturers even offer integrated electromechanical shutters, with minimum exposure times as short as 200 ms and lifetimes >10 cycles. There are many manufacturers of solar simulators, and some well-known names include Oriel Instruments (Newport), Asahi, Abet Technologies, Luzchem, Wacom, Spire, Voss, etc. 

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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