Research On Unbiased Water Splitting Hydrogen Production External-connected Device Based On Silicon Thin Film Solar Cells

Water splitting technology can not only alleviate the environmental problems caused by fossil fuel consumption,but also meet the growing energy needs.Thus,the preparation of unbiased water splitting device gradually received the attention from researchers all over the world.At present,the hydrogen production external-connected device based on semiconductors and solar cells,and the device based on catalysts and solar cells have already been the promosing technologies for hydrogen production.However,the low light harvest?high carriers recombination rate and low catalytic reaction rate limited the solar to hydrogen(STH)efficiency of device based on semiconductor and solar cells.The low catalytic reaction rate and poor contact around photoelectrode/electrolyte have been the main challenges of PV-based device for unbiased water splitting.Meanwhile,the device based on catalysts and solar cells also faced the obstacle caused by high overpotential(?)and poor conductivity of catalyst.For these purpose,this work mainly explore the ways that could solve the above-mentioned problems by choosing ZnO photoanode,Ni O_x catalyst,silicon thin-film solar cells photoelectrode and NiFe-based catalyst.Moreover,we also demonstrated the silicon solar cells based integrated hydrogen production device.Detailed studies involved are presented as follows:Firstly,in order to realize the unbiased water splitting hydrogen production of ZnO/solar cell external-connected device.We firstly deposited the ZnO photoanode by using metal organic chemical vapor deposition method.And then,improved the PEC performance of ZnO by improving the light harvest,which is mainly achieved by increasing the thickness of ZnO thin film.Then,we used the borane to prepare the B doped ZnO(ZnO:B,BZO)photoanode,which could improve the electrical property.Furthermore,we also farbicated the ZnO/BZO homojunction in order to introduce the built-in electric field,which could enhance the separation and transporation of carriers,thus,in turn,suppress the carrier'recombination and improve the PEC performance.After that,Se atoms doping and ZnOSe/ZnO heterojunction photoanode has been carried out,considering that atomic structure of Se is silimilar to the O atoms.It is found that the introduced oxygen vacancies can suppress electron back-injection,which can inhibite the carrier'accumulation and the serious recombination around the interface.Finally,we combined homojunction and hetrojunction together to supress the recombination loss and promote the carrier transfer in ZnO bulk and semiconductor/electrolyte interface.As a result,the photocurrent density at 1.23 V vs.RHE and maximum PCE value of optimized ZnOSe/ZnO/BZO photoanode can reach to 1.1 m A/cm² and 0.8%,reaspectively.Finally,the STH efficiency of external-connected hydrogen production device based on optimized ZnO photoanode and a-Si:H/a-Si:H tandem solar cell photocathode can reach to 0.7%.Secondly,aiming to the preparation of the high-performance unbiased external-connected hydrogen production device based on silicon solar cell photoelectrode and Ni O_x catalyst.We deposited the Ni O_x bifunctional catalyst by using sputtering technique.According to adjust the concentration of Ni³⁺and oxygen defects,we found that the HER performance mianly depends on the difference of Ni³⁺and oxygen defect concentration,and the OER performance mainly rely on the Ni³⁺concentration.Thereafter,we combined the Ni O_x HER catalyst with the amorphous silicon thin film solar cell to prepare solar cell photocathode for PEC water splitting.Furthermore,the PEC performance of photocathode can be further enhanced by designing double-junction a-Si:H thin film solar cells.Meanwhile,inserting a BZO back reflect layer between the solar cell and Ni O_x HER catalyst,which could decrease the carrier'recombination loss and improve the photocurrent density.The optimized solar cell photocathode could obtained saturation photocurrent density(J_SA)of 8 m A/cm²,the maximum efficiency(?_max)of 4%and onset potential(V_on)of 1.35 V vs.RHE.And then,we combined the microcrystalline(?c-Si:H)solar cells with Ni O_x OER catalyst to obtain the solar cell photoanode.Meanwhile,we use the In₂O₃:Sn layer to promote the charge transfer and suppress the holes recombination around interfaces.Finally,the V_on and J_SA of optimized photoanode can reach to 0.6 V vs.RHE and 9 m A/cm²,respectively.The?_max of soalr to oxygen can reach 2%.At last,the STH efficiency of unbiased external-connected hydrogen production device can reach to 5.9%.Thirdly,aiming to prepare the unbiased external-connected hydrogen production device based on solar cell and NiFe-based OER catalyst.We synthesized the NiFe(oxy)hydroxide OER catalyst by using the Sol-Gel method.Then,dope the borate into the NiFe host by adding Na₂B₄O₇.It is found that the added borate can change the electronic structure of Ni,which could optimize the adsorption energy of OER intermeidiate,thereby increase the NiFe catalytic ability.Furthermore,the NiFe-Borate catalyst showed the better conductivity compared to the pristine catalyst,mainly because that the borate can work as the hole-accept center.Thus,we can obtain the high-performance NiFe-Borate catalyst,whose?at 10 m A/cm² on Ni foam can reach to 200 m V.Its performance did not show clear degeneration even after 110 hours reaction.At last,integrating the NiFe-Borate OER catalyst,MoS₂:Ni HER catalyst with the a-Si:H/a-Si Ge:H/?c-Si:H,a-Si:H/a-Si:H tandem solar cells to obtain the unbiased external-connected devices,whose STH efficiency can reach to 7%and 7.4%,respectively.Moreover,we prepared the homogeneous neutral NiFe Mg catalyst using the Sol-Gel method.Improving the OER performance by introducing alkaline earth metal ions to increase the adsorption capacity of water molecules.The STH efficiency of unbiased external-connected device based on NiFe Mg OER catalyst,CoS HER catalyst and solar cell can reach 6.7%.