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Narrative Progress Report

Research Activities:

1.   We have conducted systematic experimental investigation on the antireflection properties of bio-inspired antireflection coatings on both inorganic semiconductors (e.g., Si, GaAs, and GaSb) and transparent dielectrics (e.g., sol-gel glass and polymer).

2.   A rigorous coupled-wave analysis (RCWA) model has been implemented to simulate the specular optical reflection, diffraction, scattering, and transmission from periodic subwavelength antireflective structures.

3.   A thin-film multilayer (TFM) model has been developed to simulate the specular optical reflection from subwavelength-structured surface.

Educational Activities:

1.   I have implemented two new experimental modules in the graduate class (ECH 6937 – Material Self-Assembly Over All Length Scales) I am teaching.

2.   I have recruited one high school student to work in my lab on the antireflection coating project during the summer of 2008.

3.   Three graduate and two undergraduate students have worked on the project.

4.   Three oral presentations have been made by the students at the AIChE annual meetings.

Findings:
1. We have successfully developed several inexpensive and scalable templating approaches for fabricating subwavelength-structured moth-eye antireflection coatings (ARCs) on a large variety of technologically important substrates, including Si, GaAs, GaSb, and glass.

2. The templated moth-eye antireflection coatings exhibit much improved broadband antireflection properties than traditional quarter-wavelength dielectric coatings. Normal-incidence reflection of less than 2% can be achieved on silicon, GaAs and GaSb substrates. Optical reflection of less than 1% for all optical wavelengths can be achieved for polymer and glass ARCs on transparent substrates.

3.   The moth-eye coating also exhibits superhydrophobic surface state once the aspect ratio of the nanopillars is higher than 10. This is important for developing self-cleaning ARCs for solar cells and many other optoelectronic devices.

4. Theoretical models help better understanding of the optical diffraction from subwavelength gratings, as well as rational design of moth-eye antireflection coatings for different applications. We have shown that the RCWA and TFM models create almost equivalent results for subwavelenth-structured moth-eye gratings.

Contributions within Discipline:

1. The broadband antireflection coatings enabled by our spin-coating technology can significantly improve the conversion efficiency and reduce the manufacturing cost of crystalline silicon solar cell.

2.   The optical simulation tools (RCWA and TFM) developed from this project, which are freely available from the PI's group website, facilitate fundamental understanding of optical diffraction, reflection, scattering, and transmission from various subwavelength gratings.

Contributions to Other Disciplines:

1.   The subwavelength antireflection coatings can be extended to improve the extraction efficiency of both inorganic and organic light emitting diodes.

2.   The open-sourced optical simulation codes can be implemented for other optical applications (e.g., plasmonics).

Impact on Student Education and Training:

3 graduate and 2 undergraduate students have participated in the proposed research. The multidisciplinary nature of the research program has provided a rich intellectual and scientific training ground to these students.  They have worked closely with industry (including Emcore Corporation and Jolar Technology) and other academic groups at UF as well as around the world to increase the breath of their education.

The results on biomimetic antireflection coatings have attracted great public interest. The publications have been featured on Nature, Laser Focus World, Materials Today, New England Cable TV, Popular Science, and more than thirty other public media. The PI received dozens of emails from high school students, teachers, and entrepreneurs asking about questions on the antireflection coatings and solar cells. We believe this will inspire interests of students and publics in science and engineering.

Contributions Beyond Science and Engineering:

The results on biomimetic antireflection coatings have attracted industrial interest from both start-up (Nano Terra) and big companies (e.g., REC Group, one of the biggest photovoltaics companies). REC Group is evaluating the technology for their solar cell manufacturing. We are also working with Emcore Corporation and Jolar Technology in transferring the antireflection technologies developed in the PI's lab to their commercial applications in GaAs and crystalline Si solar cells.

Impact on the PI's Career:

This ACS PRF helps to jump-start the PI's research career. Using the preliminary data obtained from this grant, the PI has successfully attracted more than $600,000 funding from other federal agencies (including a prestigious NSF CAREER award, DOE, and California Energy Commission). The work supported by this ACS PRF grant has also attracted a lot of public and industrial interest. This greatly facilitates the PI to commercialize the technologies developed in his group. A start-up company will be established in Gainesville, Florida in 2010 to commercial the antireflection technologies for efficient solar cells.