Optoelectronic Modeling Of Si/?-Fe₂O₃ Heterojunction Photoanode

The development of new technologies utilizing solar energycan fundamentally solve the energy crisis and environmental pollution.Semiconductor photocatalytic decomposition of water for hydrogen is one of the most ideal,economical and clean ways in solar-driven water-splitting systems.The photoelectrode configuration is a key ingredient to obtain the high conversion efficiency.The micro-/nano-structured heterojunction photoelectrode consisted of two absorbing materials can improve the stability of the photoelectrode,meanwhile extend the spectral absorption range.In addition,the heterojunction structure also facilitates the system to realize spontaneous water splitting.However,current experimental investigations show that in order to break through the inefficient bottleneck of the photoelectrochemical water-splitting system,the carrier transport process inside the heterojunction photoelectrode must be thoroughly and accurately understood.This work,taking Si/?-Fe2O3 dual-absorber photoanode system as an example to model and simulate the heterojunction by means of COMSOL Multiphysics software.The core research contents of this thesis are listed as follows:First,the principle and modeling process of the Si/?-Fe2O3 photoanode are clarified.This dissertation reveals the influences of the optical and electrical properties of Si and ?-Fe2O3 materials,as well as the geometrical structure of the Si/?-Fe2O3 photoanode.To figure out the underlying photoelectric simulation principles of the electromagnetic coupling and carrier transport,the basic construction steps for modeling the Si/?-Fe2O3 photoanode are given from the optical(electromagnetic wave frequency domain)to electrical(semiconductor module)aspects.In addition,this work elaborates the essential principle of the recombination in the heterojunction photoanode system,including the bulk recombination at the Si/?-Fe2O3 interface,the surface recombination at the substract/Si and ?-Fe2O3/electrolyte surfaces.Through the numerical simulation of the above photoanode system,the optical and electrical properties of the p(n)-Si/?-Fe2O3 and monolayer ?-Fe2O3 photoanode systems were discussed.Furthermore,the current distribution curves(short circuit current density,bulk recombiantion current density,and surface recombination current density)and the J-V curves are analyzed through the calculated band bending diagrams.The results show that: 1)n-Si/?-Fe2O3 photoanode system has more negative onset potential(Von =-0.72 V)than that of the single ?-Fe2O3 photoanode system,which is not observed in the p-Si/?-Fe2O3 photoanode system;2)the heterojunction interlayer combination dominates the bulk recombination of Si/?-Fe2O3 photoanode system;3)the Si/?-Fe2O3 heterojunction photoanode systems under bias can remodel the energy band bending,leading to the carrier transport direction more unidirectional under a positive bias.By simulating and analyzing the heterojunction photoanode structure under different configurations,we find that the optoelectronic properties of the multi-junction photoanode system are mainly determined by the semiconductor doping type and the inherent material properties.Therefore,detailed optoelectronic simulation can provide reference for the design and application of highperformance multi-junction photoanode system.