Silicon Nanowire Array Photoelectrode:Surface Modification And Photoelectrochemcial Applications

One-dimensional silicon nanowire arrays?Si NWs?have great application prospects in solar energy conversion,optical detector,lithium ion battery,thermoelectric devices,gas/chemical sensors due to its unique morphology and physicochemical properties.The electrical characteristics of Si NWs are inherited from the substrate,which benefits for the carrier migration between the nanostructure and the substrate.Besides,the radial junction configuration for Si NWs leads to the orthogonalization of the carrier separation and the photon incidence,as a result,Si NWs exhibit excellent light trapping performance and promising efficiency of carrier collection.However,many problems still exist.For photoelectrochemical?PEC?cell based on Si NWs,photocurrent density is too small and the stability of the PEC response is poor.For water splitting system based on Si NWs,overall water oxidation and reduction cannot be achieved without bias.In this thesis,Si NWs with uniform morphology are prepared.The Si NWs photoelectrode was configured with nanoparticles modification and thin film passivation.Properties of photoelectrochemical solar cell and water splitting system configured from Si NWs are studied.1.A new modification method of PEC cell based on Si NWs has been proposed.The Si NWs with etching time of 5 minutes?length of ³ ?m,diameter of 30-100 nm?was chosen to construct the photoelectrode.Si NWs was firstly decorated with Ag nanoparticles?diameter of ⁵0 nm?prepared by thermal reduction method.The saturation photocurrent density?Jsat?of the Si NWs was improved and the applied potential for Jsat was decreased,but the attenuation was serious.The stability was greatly improved by surface passivation with Ti O2 layer?thickness of 2 nm?,prepared by atomic layer deposition.Coating of SiO₂ layer?thickness of 10 nm?on the surface of Ag nanoparticles can lead to the suppression of carrier capture or recombination at the metal-silicon interfaces,improvement of the saturation photocurrent density,as well as good stability.Compared to the bare Si NWs,a 40% enhancement in Jsat,a cathodic shift of 0.8 V in the applied potential for Jsat,and over 10 h continuous operation with a high photocurrent density without decay were realized by using the properly modified Si NWs.2.BiVO₄/Si NWs double absorber photoelectrode for water splitting system was designed and fabricated.BiVO₄ thin films were grown on the Si NWs by cycling the impregnation and calcination.Morphology of the BiVO₄/Si NWs was controlled and material characterization was systematically conducted.The PEC response was evaluated via the PEC cell with BiVO₄/Si NWs electrode.However,photocurrent density was always low either without or with bias,the key factors limiting the system performance need further exploration.