This EArly-concept Grants for Exploratory Research (EAGER) grant provides funding for feasibility studies for the laser manufacturing of 3D silicon photonic crystals for large area solar cells. Both electrodynamic computations and experiments will be performed to explore the feasibility of nanophotonic light trapping in 3D photonic crystal photoactive regions for enhanced efficiencies in solar cells. A scalable laser manufacturing method will be developed to demonstrate preliminary results on low-cost 3D silicon photonic structures. The proposed process involves the use of laser interference lithography, chemical vapor deposition and template infiltration. This process has been simulated but not yet demonstrated for 3D silicon crystals.
If successful, the results of this research will demonstrate the proof-of-concept for a new photonic crystal solar cell structure that exhibits enhanced efficiencies and that can be manufactured at production scale and low cost. The long term goal of the research effort is to determine process-structure-property relationships for the optical absorption of laser manufactured 3D photonic crystals. The preliminary data generated here will serve as the foundation for a future study.
We used simulations to demonstrate that an optimized inverse woodpile structure with anti-reflection layer has a 72% improvement in absorption compared to an optimized anti-reflection coated silicon thin film with the same amount of silicon. The absorption in the infrared, visible, and ultraviolet parts of the spectrum may all be improved in the inverse woodpile structures compared to that of a thin film. The short circuit current density and ultimate efficiencies are also improved. Additionally, we demonstrated the ability to fabricate 3D woodpile structures in SU8 using laser holographic fabrication. 3D photonic crystal structures may be produced in SU8 with a single laser exposure and serve as a template for fabricating various photonic crystals with low-cost and quickly. We have demonstrated the ability to infiltrate these structures with TiO2 using sol-gel methods. The outcome of this research provides scientists and engineers with tools for understanding the optical properties of photonic crystals and methodologies for fabricating them with low-cost meth- ods. These structures may be utilized for other applications such as photodetectors, optical filters, and sensors. Scientific results generated from this program have been disseminated in 2 scentific papers. All of them are available on the internet. Two engineering Ph.Ds have been supported for one year each through this grant.
