Study On Betavoltaic Cell Based On Black TiO₂ Nanotube Arrays

In the extreme environments(e.g.deep sea,space,polar regions,deserts,and underground),a hot topic in micro-energy field is to provide long-life and maintenance-free power supplies for microelectronic devices(e.g.microsensors,micro actuators and microchips).The traditional conventional power supplies are restricted in the harsh environments,due to their structures and working principles.Betavoltaic cell is superior in energy density,duration and environmental adaptivity.Currently,the energy conversion efficiency of betavoltaic cell is still limited,restricts its practical application.It is a key to inprove the energy conversion efficiency of the micro-betavoltaic cell.In this dissertation,several betavoltaic cells were fabricated.Ordered titanium dioxide nanotube arrays(TiO2 NTAs)and 63Ni isotopes were used as energy conversion carriers and radiation sources,respectively.This research included the working principle investigation of betavoltaic cells,the growth and characterization of titanium dioxide(TiO2)nanotubes,the performance tests of betavoltaic cells made of different samples,and the investigation on output performances of cascade cells.In the experiments,anodic oxidation was used to prepare TiO2 NTAs(a diameter of 100 nm,a wall thickness of 10 nm and a tube length of 8 ?m).FESEM,XRD,EPR,etc.were used to characterize the morphology,crystal type and defects of the material.The experiment results showed that the betavoltaic cell made of annealed black TiO2 NTAs under irradiation of the 63Ni with a total activity of 20 mCi presented an energy conversion efficiency of 3.65%.The open-circuit voltage was 1.13 V,and the short-circuit current was 206.60 nA.The cascade output performances of the dual cells were also tested,showed that the series open-circuit voltage increased to 2.26 V,and the parallel short-circuit current increased to 416.27 nA.In theory,oxygen vacancies(OV)and Ti3+ defects formed during annealing increased the concentration of donor electrons in the semiconductor,which improved the conductivity of the TiO2.On the other hand,electron traps suppressed electron-hole pair recombination.In addition,the extreme surface curvature of the nanotubes with enhanced surface activity might result in the formation of a junction barrier between adjacent nanotubes(NT-NT junction barrier).The NT-NT junction barrier could enhance orthogonal carrier separation(holes moved to the surface of the tube wall,electrons moved to the inside of the tube wall),improved carrier lifetime and suppressed carrier recombination.This study shows that using black TiO2 NTAs with high specific surface area,highly ordered,and wide bandgap as the energy conversion material can effectively increase the open-circuit voltage and short-circuit current of the betavoltaic cell,thereby improves the energy conversion efficiency.The voltage and current output can be significantly increased by cascading betavoltaic cells.Therefore,a betavoltaic cell based on a wide bandgap semiconductor TiO2 NTAs is a potential micro-energy solution.