Investigation of Si(1-x)Ge(x) (x ≥ 0.85) Solar Cells for Affordable High Efficiency Solar Energy Conversion
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Date
2015-05
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The Ohio State University
Abstract
Increasing global demand on energy mixed with climate change is demanding a cleaner, more robust energy source. Moreover, access to low cost energy sources in much of the developing world is essential to sustain human vitality and growth. Thus, solar photovoltaics has come to the forefront of the clean energy realm as one of the most promising energy generation devices. The novel semiconductor material known as Si0.05Ge0.95 has been proposed as an ideal bottom cell (infrared sensitive) as part of a multijunction stack that has the potential to exceed 45% energy conversion efficiency in a low cost format. However, these devices have not been studied experimentally; therefore the devices must be experimentally investigated and the cells’ dependence on material properties and processing must be determined and an optimized process flow must be developed. This has been done via various processing techniques and electrical characterization tools such as lighted current-voltage, quantum efficiency (QE), and energy-dispersive X-ray spectroscopy (EDX), as part of a Department of Energy supported effort. A working device has been produced using a Ni/Ge/Au front contact, which have made ohmic contact to the material without spiking through the junction. An internal quantum efficiency (IQE) measurement greater than 50% within the 1000 – 1600 nm wavelength range has also been measured on the cell. The information obtained thus far has created a pathway forward to substantially increase the IQE within the cell, making it amenable for future integration into a final multijunction solar cell architecture that has a practically achievable efficiency limit of 45%-50%.
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Keywords
Photovoltaics, heterojunctions, SiGe, QE