Design Silicon Nanowires-Based Hydrovoltaic Device For Water-Evaporation-Induced Electricity Generation

Constant electricity generation from the natural water evaporation through appropriate device design is defined as "hydrovoltaic effect",which has the advantage of simple structure,low cost,and without additional mechanical input,etc.With regularly oriented nanochannel structure and excellent carrier transport behavior,silicon nanowires(SiNWs)-based hydrovoltaic devices that can generate constant electricity relying on the natural water evaporation process,exhibiting superior performance and environmental compatibility.Nevertheless,the state-of-the-art SiNWs based hydrovoltaic device is suffering from a slow evaporation rate(limiting driving force)and serious interfacial recombination,restraining the ultimate device performance.Furthermore,the realization of the flexibility and lightness of such devices will promote their applications in mobile energy harvesting.To tackle these challenges,this thesis focuses on composed materials,structural design,and the energy generation mechanism.First,a SiNWs array-based water evaporation-induced electricity generation device is constructed upon a bio-inspired hierarchical porous fabric electrode,which enables high water evaporation rate,rapid charge transport,and efficient charge collection,resulting in enhanced device performance.Second,to further enhance the device performance,a selective carrier transport layer is inserted at the anode and the cathode interface respectively,which effectively suppresses the interface charge recombination rate,and yields the highest value of the output power.Finally,a flexible and efficient water evaporation-induced electricity generation device is prepared based on the freestanding SiNWs mesh with the advantages of large surface/volume ratio,high nanopore density,and high surface potential,exhibiting excellent electrical properties and mechanical flexibility.The main work includes:1.A bio-inspired hierarchical porous fabric electrode consisting of graphite/conj ugated polymer poly(3,4-ethylenedioxythiophene):polystyrenesulfonate(PEDOT:PSS)/fabric is developed to construct a highly efficient SiNWs arrays-based evaporation induced electricity generation device.The fabric electrode exhibits three distinct advantages.First,the hierarchical porous structure enables highly efficient water evaporation.Second,the high conductivity of the inner PEDOT:PSS layer elevates the charge transport rate.Third,the large surface/volume ratio of the hierarchical porous structure ensures efficient charge collection.Therefore,the output performance of the hydrovoltaic device based on the fabric electrode is substantially elevated.Ultimately,the device can consistently output an open-circuit voltage of 550 mV,a short-current density of 22 μA·cm-2,and a peak power density of 10μW·cm-2 at room temperature.2.An atomic layer deposition deposited titanium oxide(TiO2)layer is incorporated on the rear side of the SiNWs array-based hydrovoltaic device,enabling high surface passivation quality and superior charge selective characteristics.The formation of the SiO-Ti chemical bond reduces the dangling bond defects on the silicon surface,which considerably suppresses the surface recombination at the silicon rear side.Meanwhile,the TiO2 interfacial layer with a rational thickness diminishes the Schottky barrier at the Si/Ag interface,enabling efficient electron transport.Finally,the device can consistently output an open-circuit voltage of 820 mV,a short-curent density of 30 μA·cm-2,and a peak power density of 15 μW·cm-2 at room temperature.3.A cobalt oxide(CoOx)interfacial layer is introduced between the SiNWs and the graphite electrode to reduce the interface charge recombination of the SiNWs array-based hydrovoltaic device.The CoOx layer acts as a hole-selective layer,facilitating selective hole transport at the anode interface.Meanwhile,the CoOx layer builds an electric field on the SiNWs/CoOx interface,which blocks the migration of electrons to the anode,and thus effectively inhibits the interface charge recombination.Ultimately,the SiNWs based-hydrvoltaic device based on the CoOx interface layer can consistently output an open-circuit voltage of 820 mV and a short-current density of 36μA·cm-2,achieving a peak power density of 17.0 μW·cm-2 at room temperature,one of the highest output power reported at that time.4.A flexible and efficient water evaporation-induced electricity generator based on the freestanding SiNWs mesh is fabricated,which exhibits excellent electrical properties and mechanical flexibility.The freestanding SiNWs mesh possesses three critical advantages.First,the large surface/volume ratio enhances the interaction area between water molecules and SiNWs.Second,the high-density nanopore structure provides a large number of nanochannels and promotes the overlapping of the double layers at the water/SiNWs interface.Third,the high surface potential increases the ion concentration within the double layer.The correlation between the device output performance and the diffusion direction,length,and rate of the capillary water flow on the SiNWs mesh film,as well as the ion species and the strength of various liquids,is further investigated to explore the mechanism of its electrical energy generation.Finally,the flexible hydrovolatic device based on the freestanding SiNWs mesh yields an open-circuit voltage of 1.5 V and a peak specific volume power of 160 μW·cm-3,which is a record value amid the reported analogous hydrovolatic devices.