Very few companies have seriously pursued black silicon solar cells as an alternative to the conventional ones often seen in typical power generation applications. However, Natcore Technology Inc. will develop highly innovative black silicon solar cells, as well as related equipment and chemicals, through a patent licensing agreement with the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Black silicon essentially does not reflect any ultraviolet sunlight when modified with nano-scale pores etched in the silicon surface. Many companies have sought ways to reduce reflectance and boost the efficiency of silicon solar cells by various types of surface modification including surface roughening.
Black silicon-based solar panels could have significantly higher power output than traditional silicon solar panels with antireflective coatings, because the reflectance from black silicon is much lower. NREL and Natcore have measured uncoated silicon solar cell reflectivity at 40 percent, which dropped to 6 percent with an antireflective coating, while black silicon reflectivity is less than 1.5 percent. Angular dependence of reflectance is critical for power conversion in morning and afternoon hours, when sunlight strikes a conventional flat solar module at an angle, which lessens power output.
Natcore uses its liquid-phase deposition (LPD) passivation process to streamline the production of black silicon solar cells without the need for extremely high temperature thermal oxide growth on silicon. Prior to the licensing agreement, NREL sent black silicon wafers with unfinished cells to Natcore, who in turn coated them with silicon dioxide prior to a passivation coating step to make the surface less reactive with air. Natcore will now optimize the combined processes and incorporate them into its antireflective device product line, which allows for all-liquid phase processing of super-low reflectivity, high-performance silicon solar cells at high volumes.
The NREL license contains a development and commercialization plan that establishes technical and market milestones for Natcore, along with a royalty payout plan. The agreement is effective over the full enforceable period for the NREL patents, which is a maximum of 17 years. Along with the patent agreement, Natcore and NREL will create commercial prototypes based on black silicon, under a Cooperative Research and Development Agreement.
In an age where solar research and development is being squeezed by shrinking capital budgets due to financial losses at many manufacturers, the announcement of new materials innovation pacts is promising for the industry. First Solar, a thin-film solar company and industry leader based in the Phoenix suburb of Tempe, Arizona, recently announced the discontinuation of its Silicon Valley advanced research and development facility. However, NREL continues to lead the US in this arena and offers many companies the opportunity to pursue higher performance materials for the green energy revolution.
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