Study On Radiative Transfer Properties Of Miro/Nanostructures In Solar Energy Applications

Absorption enhancement of solar radiation can reduce the cost of raw material and improve the efficiency of energy conversion,which is important for developing novel high-efficient solar phototermal and photovoltaic devices.Considering special radiative properity and transfer,miro/nanostrucutes have large potential in absorption enhancement.Therefore,three types of miro/nanostructures including thin films,periodic strucutures and aperiodic structures are investigated for applying to absorption enhancement of solar radiation.To find radiation behaviors in different types of micro/nanostructures,we have made programs and simulations with various numerical methods including transmit matrix method,rigorous coupled wave analysis and finitedifference time-domain method.For thin films,admittance match equtions for perfect absorption in layered absorbers with arbitrary layers are derived based on admittance match conditions.The equations are used to guide the selection of absorption materials and determine the structural parameters.Triple layered structures with ultrahin films are proposed.It is proved by theory,simulation and experiment that the layered strucutures have good spectral selective absorption for solar radiation.Moreover,they are insensitive to incident polarizations incidence with a large angle.For periodic structures,absorption in silicon nanowire and nanohole arrays is investigated.Almost the same lattice constant of optimal arrays,as well as a large number of absorptivity peaks are found for different arrays,which is well explained by the theories.To make up the lack of absorption in the wavelength range near the bandgap,thin blocks are taken in nanowire arrays.It shows that the complex structure excites absorption peaks in near infrared range to improve the integrated absorption.The absorption mechanisms of absorption peaks are revealed,and they are attributed to surface plasmon polaritons,guided modes and magnetic polaritons.For aperiodic structures,statistical analyses of absorption for a large number of cases of one-dimensional aperiodic gratings and two-dimensional aperiodic nanoholes are studied.It is proved that optimized aperiodic gratings have higher absorption than periodic gratings.However,the incremental amplitude of absorption in aperiodic gratings is quite limited,and it strongly sensitive to incident polarizations.It is found that different absorption characterisitcs by statistical results for three kinds of aperiodic nanoholes including random postion,random radus and amorphous pattern.Nanoholes with amorphous pattern can excite more guided modes,which benefits broadband absorption of solar radiation.Our work has validated that micro/nanostructures can enhance absorption of solar radiation by controlling their unique radiative properites and radiation transfer.The results found in the work provide valid appraches and theories to improve available micro/nanostructures and guide the development of novel radiation absorbers.