Photoelectrochemical conversion, efficiency

Singh P, Singh R, Gale R, Rajeshwar K, DuBow J (1980) Surface charge and specific ion adsorption effects in photoelectrochemical devices. J Appl Phys 51 6286-6291 Bard AJ, Bocarsly AB, Pan ERF, Walton EG, Wrighton MS (1980) The concept of Fermi level pinning at semiconductor/liquid junctions. Consequences for energy conversion efficiency and selection of useful solution redox couples in solar devices. J Am Chem Soc 102 3671-3677... 

The photoelectrochemical reduction of C02 at illuminated p-type semiconductor electrodes is also effective for C02 reduction to highly reduced products. The combination of photocathodes with catalysts for C02 reduction leads to a marked decrease in the apparent overpotential. At present, however, light to chemical energy conversion efficiencies are still very low, and negative in some cases. 

Nakato Y, Tsumura A, Tsubomura H (1982) Efficient photoelectrochemical conversion of solar energy with n-type silicon semiconductor electrodes surface doped with IIIA elements. Chem Lett 1071-1074... 

The performances of the photoelectrochemical cells are strongly dependent on the composition of the electrolyte solution (Fig. 17.22). A maximum conversion efficiency of ca. 80%, in correspondence to the metal-to-ligand charge transfer absorption maximum of N3 was obtained in the presence of 0.25 M LiI/0.025 MI2, whereas with the cobalt-based mediators, the best performances (ca. 50-55% of IPCE) were observed when solutions of Co(DTB)32+/3+ and Co(tTBterpy)22+/3 + were used. In the other investigated cases, Co(phen)32 1 /3 1, Co(tEterpy)22+/3 +, and... 

It is known that the photoelectrochemical cell (PEC), which is composed of a photoelectrode, a redox electrolyte, and a counter electrode, shows a solar light-to-current conversion efficiency of more than 10%. However, photoelectrodes such as n- and p-Si, n-and p-GaAs, n- and p-InP, and n-CdS frequently cause photocorrosion in the electrolyte solution under irradiation. This results in a poor cell stability therefore, many efforts have been made worldwide to develop a more stable PEC. 

Even without deposition of a metal island, such powders often maintain photoactivity. The requirement for effective photoelectrochemical conversion on untreated surfaces is that either the oxidation or reduction half reaction occur readily on the dark material upon application of an appropriate potential, so that one of the photogenerated charge carries can be efficiently scavenged. Thus, for some photoinduced redox reactions, metallization of the semiconductor photocatalyst will be essential, whereas for others platinization will have nearly no effect. 

In addition to yielding information about semiconductor charge-transfer dynamics, the fill factor parameterizes the efficiency with which the photo-electrochemical cell can be expected to convert optical energy to electricity. The practical value of a photoelectrochemical cell is usually evaluated by its maximum conversion efficiency. The energy conversion efficiency is defined as... 

In the discussions by many authors of the energy conversion efficiency of semiconductor photoelectrochemical systems, it has been tacitly assumed that the maximum theoretical photovoltages produced is the difference between E (in units of eV) and E(0x/R). The best conversion efficiency should then be obtained with a redox couple whose standard redox potential is as low as possible, with a reasonable margin x, say 0.3 V, above E (Fig. 11). From this it follows that the maximum photovoltage obtainable is equal to the band gap, Eg, in an eV unit, minus a small margin x plus A. 

Cd-chalcogenides (CdS, CdSe, CdTe) are among the most studied materials as photoelectrodes in a photoelectrochemical cell (PEC) (1,2 /3,4). Interest in such PEC s stems from the fact that, in aqueous polysulfide or polyselenide solutions, a drastic decrease in photocorrosion is observed, as compared to other aqueous solutions, while reasonable conversion efficiencies can be attained. 

Recently we showed that PEC s using alloys of Cd(Se,Te) as photoelectrodes can be prepared with stability characteristics much better than those obtained for CdTe based cells and with similar conversion efficiences (). Those efficiencies could be improved considerably by several chemical and photoelectrochemical surface treatments. 

The photoelectrochemical properties of different semiconductor materials have been widely reported, for single crystal, polycrystalline, as well as for nanostructured materials. In the literature various methods for measuring the efficiency are found. The most common is the JPCE (incident photon-to-current conversion efficiency) or quantum efficiency, which is defined as... 

---