Preparation And Solar Water-splitting Performances Of Hematite Film

Hematite(?-Fe2O3)material is regarded as a promising candidate for solar-driven water splitting because of its low cost,chemical stability and appropriate bandgap.However,the measured value of solar-to-hydrogen efficiency is far lower than the theoretical value due to the following three factors.First,the electrical conductivity of intrinsic hematite is very poor.Second,the mean free path of minority carrier is very short.Third,the oxygen evolution reaction is very sluggish.In this thesis,the solar water-splitting performance of ?-Fe2O3 film photoanode was improved from two routes(i.e.,co-doping of tin and oxygen vacancy,and embedded silicon pn junction).The main contents were summarized as follows:First,the solar water-splitting performance of ?-Fe2O3 film photoanode synthesized by ultrasonic spray pyrolysis method was improved with the co-doping of tin and oxygen-vacancy,which leads to that the current density at 1.23 V vs.RHE(Jph@i.23v)under one-sun illumination was improved 25 folds relative to the untreated counterpart.Further analysis showed that not only the conductivity of hematite was enhanced,but also the separation efficiency(surface recombination)of photogenerated-carrier in the process of transmission was promoted(suppressed)to a certain extent.Since excessive doping of tin had a negative effect on the formation of lattice structure and the stability of Fe-O,and the oxygen vacancy with too-high density could become the carrier recombination centers,the relative density should be carefully controlled.Second,the reduction of turn-on potential for the ?-Fe2O3 photoanode synthesized by hydrothermal method was realized with the photovoltaic effect of silicon pn junction.For the p+n-Si/?-Fe2O3 solar water-splitting system,with a combination of SnO2 middle layer,tin doping and deposition of Co-Pi catalyst,the turn-on potential was reduced to 0.62 VRHE from 0.9 VRHE.In addition,the intact Si photovoltaic device and FTO/Sn@?-Fe2O3 photoanode were connected in series.Finally,the turn-on potential of the three-terminal system was reduced to 0.32 VRHE and Jph@1.23v was up to 4.2 mA/cm2.It proved that the turn-on potential and applied bias could be reduced significantly with the embedded photovoltaic device,but it was a challenging to control the different interface defects and interfacial recombination between the top and bottom absorbers.At the same time,the complexity and cost of the solar water-splitting system need to be balanced.