Nanostructures with their unique physical chemical and properties show immense potential in the design and fabrication of low cost photovoltaics. To explore the various possibilities for designing an improved low cost solar cell with nanowire as the building block this research work has been carried out. In this work a single silicon nanowire structure has been simulated to study the effect of varying doping density on the solar cell parameters so as to optimise the overall quantum efficiency. Three case studies have been carried out in the process by using Silvaco TCAD’s Atlas tool-kit and an optimum set of open-circuit voltage (Voc), Short-circuit current density (Jsc), Fill-factor (FF) and efficiency(??) obtained. It has been shown that the efficiency of nanowire solar cell improves with increase in the doping density. A single nanowire provides an efficiency of 8.25% thus indicating that when many such nanowires are integrated to form an array, a much improved overall quantum efficiency can be obtained.
The sun is ever present and its rays covering the earth surface has enough power to meet more than half of the global energy demand. Although the potentiality of solar cell as a means for energy production was realised way back in 1977 but till now the technology has only been able to cross its nascent stage. This photovoltaic device is faced with certain challenges that have kept this renewable source of energy out of large scale commercial use. The difficulties include high cost and low efficiencies compared to the conventional power generation strategies like fossil fuels and nuclear. Silicon, the most preferred material for the fabrication of solar cell cannot be used in its raw form and converting the metallurgical grade silicon to solar grade silicon is highly cost intensive. The low efficiencies are due to incomplete light absorption, carrier recombination and thermalization losses. To overcome the above obstacles a lot of research is being carried out to explore new and improved avenues for solar power generation. In this regard nanostructured devices are promising candidates that could break the impasse and lead towards high efficiency and low cost solar cells.
Within the nano-world domain lies the possible source of next-generation solar cells, the ‘nanowires’. These are one-dimensional structures with a large aspect ratio and 1-100nm in diameter and offers unique advantages. Firstly due to the small diameter the radial dimension of nanowires is comparable to wavelength of light leading to efficient light absorption. Secondly the large surface-to-volume ratio results in enhanced chemical reactivity. Thirdly the inherently short charge separation distance in NWs with coaxial p-n junctions reduces the recombination losses thereby increasing the efficiency. Finally the less complex and more economic synthesis techniques for fabrication of nanowires will have significant effect on the overall cost reduction of solar cells.
3. DEVICE STRUCTURE
The device consists of a coaxial p+-n- n+ structure of length 3.1??m, simulated using three-dimensional cylindrical co-ordinate system. In this structure three different regions are defined each made up of silicon but with different doping levels. …
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