On the role of surface states in semiconductor electrode photoelectrochemical cells
Surface states that occur at the semiconductor–liquid interface play an important role in the behaviour of that interface and affect the efficiency of photoelectrochemical solar devices. The nature of such states and evidence for their existence will be briefly reviewed. Their role in dark electron transfer reactions for redox couples with energies within the band-gap region and in mediating surface recombinations will be discussed. The importance of Fermi-level pinning by surface states at moderate densities in GaAs and Si in controlling the open-circuit photovoltage and the observed electrochemical behaviour will be described. The effect of the surface pretreatment on the photoelectrochemical behaviour of p-GaAs and n-WSe2 will be demonstrated.