Abstract
An efficiency analysis of photoelectrolysis solar cells is presented which takes into account fundamental thermodynamic energy losses, as well as all major losses associated with charge transport in semiconductor photoelectrochemical cells (PECs). The analysis is performed for several values of the non-fundamental losses. By using transport properties approximately matching those of the best materials presently available, we derive “upper limit” estimates of efficiencies achievable with one- and two-photon PECs. A one-photon PEC is found to have an “upper limit” efficiency of approx. 7% (AM 1.2 solar energy to chemical potential energy stored as H 2). For two-photon configurations the “upper limit” for a p-n PEC is 10%, while for a tandem PEC it is approx. 18%. The tandem cell configuration is the least sensitive to the choice of materials parameters and transport losses and yields the highest efficiencies. The one-photon PEC is most sensitive to these choices and yields the lowest efficiencies. The relative merits of three- and four-photon arrangements are discussed in the light of these results, and compared with photovoltaics impedance matched to electrolysis cells. The relatively poor performance of unbiased PECs compared to the photovoltaic-electrolysis cell combination is largely a consequence of lack of proper impedance matching in the former, a problem shared to some degree by all photochemical energy storage systems.
Published Version
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