| The increasing depletion of fossil fuels and the environmental pollution caused by their combustion are key factors limiting sustainable human development.The development of new and sustainable alternative energy sources is the fundamental way to break the crisis.Solar energy is considered to be the most promising renewable energy source,and the use of semiconductor photoelectrochemical energy conversion technology can achieve efficient conversion and storage of solar energy to chemical energy,such as converting carbon dioxide or water into valuable fuels such as methanol,hydrogen and hydrogen peroxide.Despite its great potential,photoelectrochemical energy conversion technology has not yet been effectively applied due to its low conversion efficiency.Semiconductor photovoltaic electrodes are the core of photoelectrochemical energy conversion systems.Metal oxide semiconductors have low carrier mobility(10-3-10-1 cm·V-1·s-1)due to their polariton transport properties,which limits the diffusion distance of photogenerated carrier and makes the spatial collection efficiency of carrier lower and recombination loss serious,which is the key to limit its energy conversion efficiency.In addition,the surface passivation of semiconductor photoelectrodes and the energy level mismatch at the substrate interface are also important factors causing carrier recombination loss.In summary,the carrier loss in semiconductor photoelectrodes can be spatially divided into the surface,at the substrate interface and inside the semiconductor.Therefore,developing optimization strategies for loss mechanisms in different regions is a fundamental way to improve system performance.To address the above-mentioned problems in semiconductor photoelectrodes,this paper identifies and optimizes the carrier collection efficiency of photoelectrodes through a combination of theoretical prediction and experimental verification,which in turn significantly improves the device performance,as follows:（1）To address the carrier recombination loss due to electrode surface defects and passivation,this paper predicts that the（002）crystalline surface of Cu Bi2O4（CBO）electrode has the best structural stability and HER reaction activity by density flooding theory,and designs CBO nanorod arrays to maximize the exposure of the（002）crystalline surface by crystal surface engineering.The photovoltaic performance and its carrier dynamics analysis show that the CBO nanorod photocathode has excellent HER activity,significantly improves carrier injection and collection efficiency,and the photocurrent is 2 times higher than that of granular CBO.（2）To address the carrier recombination loss caused by energy level mismatch at the photoelectrode substrate interface,this paper starts from energy level engineering and introduces a charge transport layer between the semiconductor photoelectrode and the collector to construct an efficient charge transport channel.Taking the Bi Fe O3（BFO）photocathode as an example,a La Ni O3（LNO）charge collection layer is introduced between the BFO and the FTO conductive substrate,and the Schottky contact is optimized as an ohmic contact to effectively reduce the hole transport potential barrier.The composite photocathode significantly enhances the device photocurrent by up to200%,while the production efficiency is nearly 2 times higher than BFO film and the Faraday efficiency is improved by a factor of one in the H2O2 photochemical generation test.（3）To address the carrier recombination loss due to the lack of electric field in the photoelectrode phase,this paper achieves gradient self-doped homojunction through ordered defect modulation,and then constructs a full-domain spatial electric field.Taking the Bi Fe O3（BFO）photocathode as an example,the full-domain spatial electric field effectively promotes the separation and transport of photogenerated carrier and suppresses the complexation,thus significantly improving the spatial collection efficiency of carrier.Under the positive electric field,the BFO photocathode photoelectric performance is improved by a factor of 2,and the H2O2photoelectrochemical production rate is increased by 69%.This thesis addresses the core problem of carrier spatial loss in semiconductor photochemical energy conversion systems,and adopts a theoretical and experimental approach to discrete carrier transport spatially,and to investigate the loss mechanisms and propose corresponding optimization strategies.This thesis enriches the design strategy of high-performance photovoltaic electrodes and promotes the development of solar to clean fuel conversion. |
