Study Of Si Based Nano/microstructures High-efficient Solar Cells

Solar photovoltaic conversion is a very important one in the new energy utilizations,and it plays an irreplaceable role in solving the fossil energy crisis and environmental protection.Solar cell is a device translating solar energy into electric energy,and thus both improving the optical gain and lowering the electrical loss are very important things to obtain high values of energy conversion efficiencies.Crystalline Si solar cells whose permanent topic is to increase the conversion efficiency and decrease the production cost,dominate the solar photovoltaic industry.Silicon?Si?based nano/microstructures?N/M-Strus?consisting of micro-textures and nanostructures,possess near zero and independent-angle reflection,as well as they have superiorities in suppressing the electrical loss from the controlled morphology when the equal reflection is kept.For the preparation of Si based N/M-Strus,we first prepare the micro-textures by employing the alkali or acid etching process consist with production line,and then the Si nanostructures are formed on the surface of micro-textures by the metal-assisted chemical etching?MACE?.MACE is a simple,low-cost,large-area preparing and recyclable process.Importantly,MACE process is completely compatible with current production line,meaning that the whole process of Si based N/M-Strus is seamless coupling with the current production line,which is beneficial to the mass production of Si based N/M-Strus based high-efficient solar cells.In this dissertation,by employing the MACE technique,we prepare the large-area crystalline and multi-crystalline Si based N/M-Strus and achieve effective passivation of the prepared Si based N/M-Strus by several dielectric thin films.Study on the optical and electrical performance shows very promising applications to the crystalline Si solar cells.Finally,we have made great progresses on the conversion efficiencies of the Si based N/M-Strus based solar cell as follows:Firstly,we have simultaneously achieved the lowest reflection?1.38%?and surface recombination velocity?44.72 cm/s?by using ALD?Atomic Layer Deposition?-Al₂O₃ passivated crystal Si based N/M-Strus?125×125mm²?,which breaks the limits of optical-electrical tradeoff in Si based N/M-Strus.The key to success lies in the abnormal electrical property meaning that Si based N/M-Strus with thinner nanowires possess higher lifetimes due to the stronger passivation effect in the longer-and-thinner nanowires from the field effect passivation.Also,Si based N/M-Strus with longer-and-thinner nanowires have lower reflection,which is attributed to the complementary antireflection from the Si based N/M-Strus and SiN_x:H thin films.Based on the simultaneous realization of the best optical and electrical performance,we have designed and simulated the n-type large-area Si based N/M-Strus based solar cells.The simulated results show an efficiency of 21.04%,which opens a broad way to the large-area mass production of Si nanostructures solar cells.Secondly,we have successfully fabricated 20.0%-efficient crystal Si based N/M-Strus based solar cell with a standard solar wafer size of156×156 mm² by employing the simultaneous stack layers SiO₂/SiN_x passivation for the front and rear surface of the cell.The high energy conversion benefits from the excellent broadband spectral response of the solar cell,which is attributed to the improved short wavelength spectral response from stack layers passivated Si based N/M-Strus based n⁺-emitter and long wavelength spectral response from stack layers passivated rear surface.Based on the improved short and long wavelength spectral responses,we obtained an efficiency of 20.0%as well as a high open-circuit voltage of 0.653 V and a large short-circuit current density of 39.0 mA/cm².The screen-printed Si based N/M-Strus high-efficient solar cells have shown very promising potentials for the mass production.Finally,we have prepared morphology-smoothened multi-crystalline Si based N/M-Strus by one-step MACE technique,and achieved an efficiency of 17.63%of the multi-crystalline Si based N/M-Strus based solar cell with a standard solar wafer size of 156×156 mm²,which surpasses the 17.45%-efficiency of the traditional acid textured multi-crystalline Si solar cell.The study on the optical performance manifests a better optical gain from the combined antireflection of Si based N/M-Strus and SiN_x:H thin films,as well as the surface recombination,Auger recombination and Shockley-Read-Hall recombination losses are controlled in a very low level by using the shorter one-step MACE smoothened morphology?without PS defects?.The key to surpassing the efficiency of traditional solar cell lies in the careful balance between the optical gain and electrical loss.The successful application of the one-step MACE multi-crystalline Si based N/M-Strus will strongly drive the mass production of multi-crystalline Si nanostructured solar cell.