The electronic properties of synthetic single crystalline pyrite 〈100〉 orientation are investigated. The spectral response of the photoconductivity was determined by the four point probe technique. The carrier concentration and the flat band potential are calculated from capacitance measurements, the minority carrier diffusion length, Lp, is determined by photocurrent and capacitance vs voltage measurements. The results, ND - NA ∼ 1 × 1018 cm-3, Lp = 0.13 μm and Vfb = -4.55 eV (relative to the vacuum level), allow the construction of an energy band diagram for the FeS2/electrolyte contact. The parameters determined explain the high quantum efficiency (∼ 90%) obtained with FeS2/I-, I3- photoelectrochemical cells (PECs). The reasons for the main deficiency (photopotentials not exceeding 200 mV at AM0) are elaborated: photogenerated changes in the interface shift the flatband potential and trap-assisted electron transfer through the barrier short-circuits it.
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