Performance And Application Of Solar Photo-Thermal Conversion Based On Low-dimensional Semiconductor Materials

With the depletion of fossil fuel and the pollution of the environment,human beings currently faced with two main problems:the increasing demand for energy,and the shortage of fresh water resources.For this reason,the use of the renewable energy,especially the abundant solar energy resources,has become the main choice for people.The light-to-heat conversion is one of the most direct and effective way to use solar energy.In addition to common solar water heaters,the light-to-heat conversion technology can also be applied to heating and cooling,seawater desalination,and light-to-heat（steam）power.As the main part of the light-to-heat conversion technology,the solar absorber is required not only to efficiently absorb sunlight and convert it to heat,but also to make effective use of the heat.The previous researches on solar light-to-heat（steam）conversion focuses mainly on the development and design of the materials that absorb sunlight and convert it to heat.The main materials and structures include carbon-based materials,polymer gels,metal-plasma structures,metal-carbon composite structures,and hierarchical nanostructures,etc.After unremitting efforts,researchers have developed high-efficiency light-to-heat conversion devices with a solar absorption rates of more than 95%and applied them to seawater desalination.However,most of them depend on continuous,stable,and vertically illumination.When the light irradiate on the surface of the absorber from multiple angles,that will cause some loss of the incident solar energy.Also,the light-to-heat conversion devices can be easily corroded by salt in the application of seawater desalination,causing a decrease in its light-to-heat（steam）conversion efficiency.In addition,the efficient light-to-heat conversion devices usually undergo large heat losses in a non-vacuum room temperature environment.Inspired by the nature,we have designed the solar light-to-heat conversion devices with a three-dimensional hierarchical structure to solve the problems above.In order to enable the device not only to achieve high efficiency solar absorption and light-to-heat conversion under multi-angle lighting conditions,but also to maintain long-term and stable salt resistance,we have designed the solar light-to-heat conversion device based on a hierarchical copper-silicon nanoparticle/nanowire structure.The device combines the superhydrophobic properties of the micro-nano structure on the lotus leaf surface with the light trapping effect of the three-dimensional nanowire structure.It can effectively expand the absorption spectrum of silicon materials,and improve its light absorption efficiency and the ability to capture sunlight in all directions.Further,we have proposed the solar light-thermal battery technology to expand the operating temperature range of high-specific-energy solid-state energy storage devices based on the designed light-to-heat conversion device.Aiming at the problem that most of the light-to-heat（steam）conversion device depend on continuous illumination and usually undergo large heat losses in a non-vacuum room temperature environment.We have designed another light-to-heat conversion device based on the graphene-honeycomb heat capture stucture with a three-dimensional hierarchical trapping effect.The device has achieved efficient light-to-heat conversion ability based on the excellent light absorption and light-to-heat conversion performance of the graphene material.And the device can effectively suppress heat loss through hierarchical heat trapping structure.1.We have prepared a solar light-to-heat conversion film（device）with hierarchical copper-silicon nanowire structure by taking full advantages of the nanowire growth technology based on vapor-solid（V-S）and vapor-liquid-solid（V-L-S）.The film achieves omnidirectional efficient solar absorption and light-to-heat conversion through the copper-silicon nanoparticle/nanowire structure.We have not only studied the solar absorption and light-to-heat conversion properties of the film,but also studied its stability and superhydrophobic properties.The results show that the solar light-to-heat conversion film based on the hierarchical copper-silicon nanowire structure has two superhydrophobic surface（water contact angle of156°）.The film can achieve efficient solar absorption and light-to-heat conversion in the range of sunlight’s incident angles from 0°to 80°,and obtain a high solar absorption efficiency（spectrum range:200-2500 nm,the efficiency up to 93.8%）under vertical light irradiation.In addition,the film shows an excellent stability of solar absorption and light-to-heat conversion after being irradiated by very strong light(irradiation power:16000 W·m^-2).2.In order to solve the problem of poor salt resistance of the light-to-heat conversion devices,we have applied the solar light-heat conversion film baesd on hierarchical copper-silicon nanowire structure to purify the seawater.During this process,the sunlight is absorbed and converted into heat through the hierarchical copper-silicon nano-particle/nano-wire structure of the film.And the seawater is extracted by the hierarchical silicon nanowire/copper-silicon nanowire structure of the film.The device for solar seawater desalination based on the solar light-heat conversion film achieves a high solar light-to-heat（steam）conversion efficiency（～86%）under one sun irradiation(AM1.5,1000 W·m^-2).In addition,the device’s super-hydrophobic surface characteristics enable it to float naturally on the water,and maintain excellent salt resistance and long-term cycling stability.3.Based on the light-to-heat conversion technology,we have proposed a concept of solar photo-thermal battery to expanding the operating temperature range of the energy storage device.We use the solar light-to-heat conversion film baesd on hierarchical copper-silicon nanowire structure to replace the traditional copper foil as a solar photo-thermal current collector of the solid-state lithium-sulfur battery.The first solid-state lithium-sulfur battery operating in a wide temperature range of-60℃to 60℃has been realized based on the solar photo-thermal current collector.The battery is able to release a capacity of about 1250 m Ah·g^-1 at-60℃.This technology provides a new idea for developing high specific energy battery systems operating in a wide temperature range,which can greatly expand the application field of the energy storage devices.4.Aiming at the problem that most of the light-to-heat（steam）conversion device depend on continuous illumination and usually undergo large heat losses in a non-vacuum room temperature environment.We have prepared a high-efficiency light-to-heat conversion device with a heat-trapping effect based on hierarchical graphene-hive structure.The device has achieved a solar absorption rate of up to97%in the full spectral range（200-2500 nm）and an efficient heat trapping and storage.The solar seawater desalination device based on the hierarchical graphene-hive structure achieves an initial solar-thermal（steam）conversion efficiency of about 85%under continuous irradiation(AM1.5,1000 W·m^-2).In addition,the excellent heat storage performance of the device not only has improved its solar-thermal（steam）conversion efficiency（about 9%）during the cycle test under continuous irradiation of one sun,but also has improved its solar-thermal（steam）conversion efficiency under discontinuous irradiation of one sun.In one hour,the steam’s production under discontinuous irradiation reaches 81%of the production under continuous irradiation.It provides an idea for the design of high-efficiency solar seawater desalination devices working in all weather（sunny or cloudy）.