Selective Absorber/emitter And Its Applications On Solar Thermal Conversion

Solar thermal conversion technology,which is one of the most vital solution to energy crisis,has important applications in photovoltaic,thermal energy storage and water treatment.Solar selective absorber/emitter is the key element in solar thermal conversion.In this thesis,several micro/nano-structured solar selective absorbers/emitters have been proposed and fabricated with simple and large-scale nanotechnologies.First we demonstrated a large-scale nanostructured low-temperature solar selective absorber experimentally.It consists of tantalum nanopatterns assisted by self-assembled closely-packed polysterene nanospheres and a silicon dioxide thin film coating.Due to the strong light harvesting of the surface nanopatterns and constructive interference within the top silicon dioxide coating,our absorber has a much higher solar absorption(0.84)than its planar counterpart(0.78).Though its solar absorption is lower than that of commercial black paint,the greatly-suppressed thermal emission in the long range still enables a higher heat accumulation.Under 7-sun solar illumination in ambient conditions,the balanced temperature is as high as 196.3 ?,which is much higher than those achieved by the two comparables.Then we studied the selective absorber/emitter based on ultrathin hemispherical shell structure.We demonstrated an ultrathin nanostructured solar selective absorber based on hemisphere structure.Is consists of a self-assembled tungsten hemispherical shell array,a coating of ultrathin germanium film and a silicon dioxide antireflective coating.Due to the combined effect of surface plasmon polaritons on the interface of tungsten and germanium,unconventional interference inside ultrathin lossy dielectric film and antireflection,selective absorber has achieved a higher solar absorption than planar structure,almost equal to that of black paint.In the long wavelength region,strongly suppressed emission allows better heat accumulation.Under 7-sun illumination,selective absorber achieved a working temperature of 218?,much higher than its counterpart and black paint.Subsequently,we demonstrate a solar selective absorber based on hemispherical bowl structure.It consists of a tungsten bowl array covered with a ultrathin germanium film and a silicon dioxide antireflection film.The simulation and experimental results show a similar behavior as the absorber based on the spherical shell array:high absorption in the short wavelength region and suppressed emission in the long wavelength region.Furthermore,a combined design is demonstrated combining a solar selective absorber and a thermal selective emitter together.The solar selective absorber is based on a silicon micropyramid array on top of which tungsten,germanium and silicon dioxide are deposited in sequence to have a high solar thermal conversion efficiency.It reaches a working temperature over 230? under 7-sun illumination.In the aspect of the thermal selective emitter,we apply Tamm plasmon polaritons to achieve a narrow selective emission characteristic.Given the working temperature of 200 ? the geometrical parameters are optimized by numerical simulations.The room-temperature absorption spectrum of the emitter is characterized,showing good potential for selective emission.The difference between simulation and experimental results is carefully discussed and analyzed.Finally,we make a conclusion about our work and the thesis,and we make a discussion about the solar selective absorber/emitter research and its application in the future.