Study Of Nanowires Based High Performance Radial Junction Silicon Thin Film Solar Cells

Throughout the history of human civilization,the rapid development of science and industry is always accompanied by a great consumpsion of energy and the terrible pollution of our environment.The limited fossil fuel is suffering exhaustive exploitation and overuse,which remarks the ponderance of the energy shortage problem.It has become urgent that new alternative and green energy sources and technologies have to be established and implemented in a world-wide large scale,in order to curb the green-gas emission and switch smoothly into a sustainable growth and development pattern.To this end,the development of clean energy source technologies such as wind power,photovoltaics and bio-system are gaining remarkable momentums in recent years.Particularly,according to the prediction of international energy agency?IEA?,the percentage of renewable energy will amount to more than 33%by 2030,wherein solar energy will account for a large portion thanks to its long-term and basically inexhaustible availability and zero-impact to local ecosystem.So far,the most appealing large scale and commercially profitable PV technology is based on bulk crystalline or polymorphous silicon?Si?technology,with a dominant market share>85%.Among them,thin film hydrogenated amorphous Si?a-Si:H?can be deposited at a far low process temperature over large substrate,making them ideal candidate for low-cost,flexible and distributed PV applications.However,the wide application of a-Si:H thin film solar cells has been largely limited by the higher defect density in the disorder a-Si:H material and the light-induced-degradation?LID?upon lasting exposure to sunlight.In order to counter these drawbacks,a new architecture of radial junction?RJ?solar cells upon well-defined Si nanowires?SiNWs?framework is emerging as a promising strategy to boost the PV performance of thin film solar cells.Herein,we make a systematic research on the performance optimization of RJ solar cells through the method of experiments and simulations.In summary,the major innovations in this thesis can be summarized as follows:1.Exploring a low temperature growth of Si nanowires,via a low-melting-point metal catalyzed VLS process.To be applied as the 3D structure of Radial junction solar cells,the as-produced SiNWs are doped into p-type and 1.7?m long,40 nm in diamerer?in the middle,which sharply tapering to 20nm at the tips?.2.Fabricating high performance radial junction thin film solar cells,via a systematic parametric optimization and structural control,with a power conversion efficiency higher than 8.2%.Resting upon the solid experimental basis,we also assess a more advanced tandem RJ structure with radially stacking a-Si:H/nanocrystalline Si?nc-Si:H?PIN junctions,and show that a balanced photo-current generation with a short circuit current density of Jsc=14.2 mA/cm² can be achieved in a tandem RJ cell,while reducing the expensive nc-Si:H absorber thickness from 1-3?m?in planar tandem cells?to only 120 nm.3.Accomplishing the first radial junction a-SiGe thin film solar cells,with a largely extended absorption spectrum to 900 nm wavelength and a V_oc of 0.63V,a efficiency of 5.78%.4.Reporting a novel p-type copper oxide nanowires?CuO NWs?/a-Si:H thin film solar cells,which can be fabricated conveniently in a large-area thin film process,with a full compatibility with the conventional a-Si:H thin film technology.The simple CuO NW/a-Si:H/n-a-Si:H radial junction cell exhibits an unexpected high open-circuit voltage of Voc=740 mV.