Monthly Archives: July 2010

Since the introduction of solar energy, the standard material used for photovoltaic cells, as well as most electronic devices, has been silicon or, more expensively, crystalline silicon. This is in accordance to market attributes such as supply, demand, and manufacturing costs. Accordingly, although it is the most viable material to include in photovoltaic cells, it is far from the most efficient. An example of a significantly more efficient material is gallium arsenide, but its cost renders its inclusion in the manufacturing process too expensive to permeate the mainstream.

To approach this problem, professors John Rogers and Xuiling Li of the University of Illinois sought ways to manufacture gallium arsenide more cost effectively. Rogers, the Lee J. Flory Founder Chair in Engineering Innovation as well as professor of materials science and engineering, stated that the identification of a cost effective method to produce gallium arsenide could expand its application to a variety of mainstream markets, to include photovoltaic apparati. After a period of detailed research, the resulting solution that the team found was to apply the gallium arsenide to a base differently.

Traditionally, gallium arsenide is simply applied to numerous wafers. A wafer is the base on which circuitry and other electrical components are usually superimposed. Using this new, cost effective method, gallium arsenide would be applied to a single wafer in layers, requiring the use of a single wafer in order to create all of the necessary circuitry with the gallium arsenide at the same time. The team accomplished this by first coating the wafer with aluminum arsenide, then alternating each gallium arsenide layer with a layer of aluminum arsenide.

The result is an intermittent stack of aluminum arsenide and all of the gallium arsenide that one would need for an application. The wafer is then placed in a solution of acid and oxidizers, which dissolves the aluminum arsenide, leaving separated sheets of gallium arsenide. A machine with an appendage that has a stamp-like surface at the end then removes each layer, leaving a clean wafer behind that can be reused, rendering the manufacturing process much less time consuming. Furthermore, production completed in this manner would require less materials and preparation. As a result, overall manufacturing costs would be reduced significantly, enabling the use of more effective materials like gallium arsenide.

Another benefit of this new process is the elimination of photovoltaic cell size constraints. Previously, photovoltaic cells were limited to the size of the wafers on which each layer of circuitry was produced. Now, multiple duplicates of the same layer can be created on a single wafer, granting the potential to engineer photovoltaic cells that are literally exponentially larger.

The team partnered with two scientists, Matthew Meitl Etienne Menard from Semprius, Inc., to publish an article in Nature on May 10 describing the new process as well as potential applications and improvements. Other members of the Department of Energy and National Science Foundation are Drs. Jongseung Yoon, Sungjin Jo, and Inhwa Jung; students Ik Su Chun and Hoon-Sik Kin; and electrical and computer engineering professor James Coleman as well as student Ungyu Paik from Hanyang University in Seoul. Moving forward, the team intends to find further applications of the new process and new materials that can increase the efficacy of such electrical components.