Broadband Absorption And High-efficiency Hot-carrier Solar Cells

There are mainly two ways to use solar energy,including solar photovoltaic and solar thermal conversion.In order to achieve a high efficiency,both of the two conversion ways required full absorption of sunlight.Surface plasmons(SPs)are strong interactions between incident light and surface electrons in metal,generating extremely strong electromagnetic field around the metal surface and thus possessing outstanding light trapping and manipulation properties.Taking advantage of SPs effect,this thesis firstly discusses the broadband absorber based on the metal nanostructure.On the basis of excellent absorption and light trapping of nanostrcture,we further discuss the design and realization of a hot-carrier solar cell.First,we propose a three-layer broadband absorber based on a hexagonal densely arranged single-layer W nanobowl array.We use FDTD to establish a simulation model and optimize the structural parameters.The optical properties of the absorber in the range of 0.4-2 ?m are discussed.According to the optimized parameters,a hexagonal close-packed 2D W nanobowl array was prepared by self-assembly method,and then Ge and SiO2 were deposited on it.The experimental results show that almost 100%of light is absorbed by this absorber in the range of 400-800 nm,and the absorption falls rapidly in the range of 800-2000 nm.The whole device achieve perfect absorption of short wavelength and suppress the long wavelength radiation.Then,we designed an efficient hot carrier photovoltaic solar cell.Localized surface plasmon polaritons(SPs).which can decay non-radiatively into hot carriers,have been widely employed to extend the responses of traditional semiconductor-based photocatalytic and photovoltaic devices to sub-bandgap photons.However,radiative decay is unavoidable and adverse to device performances.Here,we propose to take advantage of propagating SPs,another form of SPs.which possess non-radiative decay only.A special gold-titanium dioxide nanowire array with each nanowire capped with a nanocone is proposed.The adjacent nanocones forming top gradual openings attribute to efficient sunlight harvesting,while the neighbouring nanowires forming bottom nanoslots allow sufficient absorption due to the propagating SPs.With the combined advantages,almost 100%of light is absorbed by a very thin gold film in the visible range,and 73%in the whole considered range of 400-1170 nm.superior to the nanocone cell based on localized SPs,let alone the nanowire-based and planar counterparts.Therefore,much better photovoltaic conversion performance is achieved with short-circuit current density of 0.74 mA/cm2 and open-circuit voltage of 0.41V.This work confirms the superiority of non-radiative decay of propagating SPs to the localized SPs in terms of generation of hot carriers,providing a promising way of extracting electrons in metal into photocurrent.