| As the energy crisis and environmental deterioration become more and more serious,the exploration of clean and sustainable energy becomes an important research target all around the world.Solar energy plays an important role in the global renewable energy development strategy due to its advantages of large amount,cleanliness,unpaid,and no geographical region.In order to promote the large-scale application of solar energy,the key issue of its industrialized application is how to effectively use solar cell at this stage.Many researchers found that photon management by micro-structured surface can availably improve the utilization of solar energy via reducing the optical loss.However,the microstructured surface would enhance the surface recombination,resulting in the degeneration of the photoelectrical conversion efficiency.Therefore,it is of great significance to understand the physical mechanisms of enhanced absorption and carrier rembination by microstructures.In this thesis,the aim is to improve the utilization of solar energy.The effects of microstructures and carrier recombination on the performance of the photovoltaic cells,photovoltaic-thermoelectric hybrid systems,and thermoelectric generators are investigated.The effects of the microstructured surface and carrier recombination in the process of the solar energy capturing,absorption,transport,and transfer are revealed.Our study can provide a theoretical basis and design criteria for highly efficient utilization of solar energy.The details of the specific research include the following aspects:1.Effects of microstructures on the photoelectric properties of the silicon thin-film solar cellsAlthough the micro-structured surface can effectively improve the photon trapping ability,it also brings the problems of surface recombination enhancement at the same time.It is well known that carrier recombination is detrimental to the performance of the solar cells.On the basis of the photoelectric coupling model,the optoelectronic properties of micro-structured silicon thin-film solar cells are studied in terms of surface recombination and temperature effects.The grating micro-structured surface is selected as the research object to investigate the effect of surface recombination on the performance of solar cells.The effects of surface recombination velocity and geometric parameters are investigated.With regard to temperature effects,micro-structured surfaces with nanopillars and nanoholes are investigated.The effects of temperature on optical properties,electrical properties,and structural parameters are analyzed to illustrate the impact level of the temperature on the performance of the thin-film solar cells.2.Quantifying energy losses in planar perovskite solar cellsThe energy losses in planar perovskite solar cells are quantitatively assessed in terms of underlying physical mechanisms.The photoelectrical coupling model is developed to investigate the energy loss mechanisms of CH3NH3PbI3-xClx perovskite solar cells.Five energy loss mechanisms are quantified,such as thermalization loss,below bandgap loss,optical loss,recombination loss,and spatial relaxation loss.The effects of the optical properties,carrier diffusion length,surface recombination velocity,and series resistance on the performance of the perovskite solar cells are analyzed to identify the dominant loss contributors limiting the power conversion efficiency of the perovskite solar cells.Our investigation provides a detail guideline for the design of highly efficient perovskite solar cells.3.Effect of micro-structured surface on the performance of photovoltaic-thermoelectric hybrid systemBoth the photon and thermal management approaches are proposed to increase the solar energy utilization efficiency in photovoltaic-thermoelectric(PV-TE)hybrid systems by spectrum control.The theoretical modeling is established to investigate the performance of PV-TE hybrid system.Based on the photon management strategy,a combination of bio-inspired moth-eye antireflective structured surface and enhanced transmission film are proposed to realize an effective photon management.The effects of geometric parameters,incident angle,and polarization state on the performance of PV-TE hybrid system are investigated.Thermal management plays a crucial role in affecting the performance of PV-TE hybrid system.The cooling method on the performance of the PV-TE hybrid system is investigated under different working environments.The impacts of optical concentration ratio and thermal concentration ratio on the performance of PV-TE hybrid system are investigated.4.Experimental investigation of micro-structured Si/PEDOT:PSS heterojunction solar cellsFor the wide-angle and polarization-insensitive spectral requirements of solar cells,the hybrid nano/micro-structured surface is experimentally fabricated by using anisotropic wet etching and metal-assistant chemical etching.The optical properties of hybrid structured surface are systematically investigated.The effects of etching parameters on the surface morphology and optical reflection properties are investigated to determine the optimal structured surface.The optical reflection features of different textured surfaces including planar,pyramid,black silicon,and hybrid nano/micro-structures are compared.Besides,the angle-dependent and polarization-dependent properties of these different structured surfaces are analyzed.Based on these different structured surfaces,the PEDOT:PSS/n-Si heterojunction solar cells are fabricated without destroying the microstructures.The current density-voltage characteristics of different structured surfaces under AM1.5G illumination conditions are analyzed.5.Improving the performance of the solar thermoelectric generators by selective solar absorberSelective solar absorber should have high absorption over the whole solar spectrum and low emission in the mid-infrared region.A novel type selective solar absorber to achieve high-efficiency solar thermoelectric generators is proposed under AM1.5G conditions.The effect of geometric parameters is studied to get the trade-off between the solar absorption and the mid-infrared emission.Furthermore,the effects of the incident angle and the polarization angle on the spectral absorption are studied to show the angular and polarized characteristics.The effects of thermal concentration and lattice arrangement on the performance of the solar thermoelectric generators are investigated as well.Finally,the performance of different structured surfaces is compared to illustrate the superiority of our proposed structures.The theoretical method of improving the performance of solar thermoelectric generators by micro-structured surface is established. |
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