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Solution-based Manufacturing Technologies Show Promise for Cheaper, More Efficient Solar Cells

Written by: 
Jeff Morse, PhD

Credit: pixor, flickr
While conventional solar cell technology based on crystalline silicon continues to dominate the markets, thin film technologies are rapidly becoming competitive due to improved trade-offs between cost and performance. In order to grow the solar cell markets and render them viable without government subsidies, further improvements in both cost and efficiency will be necessary. Startup company Natcore is commercializing a novel solution-based manufacturing technology that holds the promise of simultaneously improving cell efficiency and reducing production costs. Natcore is further combining this technology with an advanced anti-reflection technology, called black silicon, which has been licensed from the National Renewable Energy Laboratory in Golden, CO. Black silicon, which only impacts silicon solar cell technology, refers to the black appearance of the silicon after forming nanopores in the surface that eliminate reflection of light, which in turn improves the overall absorption of sunlight. A further advantage of black silicon is the improvements in average daily power generation as angular reflection is significantly reduced during morning and late daytimes.

The solution-based manufacturing process being commercialized by Natcore was developed at Rice University deposits a passivating anti-reflection coating in a low-temperature, liquid phase deposition process rather than the high-temperature gas-based process typically used now. Due to the difficulty of producing a uniform coating for solar cells, manufacturers do not use liquid-based processes for antireflection coatings. The desired coating is difficult to achieve due to the way it forms in a liquid process; as reactants are expended during the interaction with a surface, deposition rates fluctuate and produce a nonuniform coating. By restocking the reactants and observing film thickness, Rice researchers were able to produce a uniform coating. The high-temperature processes used on a standard manufacturing line can be replaced by the liquid-based process, lowering manufacturing costs, including annual electricity costs, while providing a path to sustainable, large area production and scaling.

Natcore is simultaneously developing more advanced applications of the process, including fabrication of solar cells made of carbon nanotubes or nanoscale crystals called quantum dots. Future solar cells manufactured using these nanomaterials could far outperform conventional solar cells. As an example of one of Natcore's advanced nanomaterial solar cell designs, layers of quantum dots are deposited on a silicon solar cell. The quantum dots are designed to absorb colors that silicon is transparent to, potentially doubling the solar cell efficiency. While this has been tried before, the challenge is to achieve optimal dispersion and spacing of the quantum dots in a low cost, scalable process. The low cost Natcore process coats quantum dots with a silicon dioxide layer, acting as a spacer and allowing for control over their arrangement. To encourage industry adoption, Natcore is coating conventional silicon solar cells, but in the future may move completely to a quantum dot based solar cell. This model would use multiple types of quantum dots to efficiently absorb sunlight wavelengths.

Reference: Bullis K. 2012. New manufacturing tech could mean cheaper solar cells. technology review

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