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September 2011

Three-Dimensional Modeling Takes on Solar Device Challenges

Looking into the performance of nano-architectured solar cell devices just got easier with math and models

Gene Nolis

Solar cell architecture and charge generation/separation for each. The nanostructured devices are intended to outperform conventional, planar ones. Also, the nanostructured device model shows an interdigitated system of positive- and negative-type materials.

Imagine reducing time to model materials systems by a factor of 1000 or more. Remarkably, researchers with the Center on Nanostructuring for Efficient Energy Conversion did just that by developing a novel analytical method. The team used this method to compare solar cell energy conversion efficiencies for various material structures.

The lure of solar cell technology, aka photovoltaics, stems from the promise of a limitless and environmentally friendly source of electricity; coupled with the ever-increasing demand for energy, photovoltaics are receiving increased research attention. In photovoltaic devices, creation of an electric current occurs when solar radiation, that is, photons, excite electrons at a p-n (positive-negative) junction. The junction acts as a two-way road, allowing photo-excited charges to flow in opposite directions, leading to an electric current.

Existing theoretical studies do not fully account for the three-dimensional behavior of solar cell devices, due to the computational resources necessary to integrate mathematical models. “When we [the research group] tried to do the simulations numerically on an 8-core processor, it would take up to 3 days for each data point,” said Artit Wangperawong, lead researcher on the study. “We then took an analytical approach to the three-dimensional problem, which allowed us to produce a data point in less than a minute on a single core.”

The team used the novel analytical method to demonstrate that interdigitated (visualize interlocking fingers of two clasped hands) junctions can offer superior energy conversion performance over planar geometries and isolated junctions. For example, in interdigitated junction modeling, multiple p-n interfaces are simulated, which allow photo-generated charges to diffuse to any nearby junction. Isolated junction modeling accounts for one primary charge diffusion path, which does not accurately reflect three-dimensional behavior.

The group’s time-saving modeling technique has enormous potential in modeling nano-structured geometries and materials systems, as well as systems beyond photovoltaics. While a commercially available simulation tool is a distant goal, Artit says, further developments may be forthcoming with continued research.

More Information

Wangperawong A and Bent SF. 2011. Three-Dimensional Nanojunction Device Models for Photovoltaics. Applied Physics Letters 98, 233106(1-3). DOI: 10.1063/1.3595411.

Acknowledgments

Studies were carried out as part of the Center on Nanostructuring for Efficient Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences. A Wangperawong acknowledges support from two sources: DOE, Office of Science Graduate Fellowship Program, made possible in part by the American Recovery and Reinvestment Act of 2009, and the National Science Foundation.

About the author(s):

  • Gene Nolis recently completed his B.S. in Chemistry at SUNY at Binghamton. He will pursue graduate studies as an ERASMUS MUNDUS scholar in the Materials for Energy Storage and Conversion Master's program. His research interests lie in understanding thermal stabilities of layered transition metal phosphates for rechargeable lithium battery materials.

A New Dimension in Solar Devices

New computational model considers electron motion in three dimensions

Solar cell architecture and charge generation/separation. The nanostructured devices (right) are intended to outperform conventional, planar ones. Also, the nanostructured device model shows an interlocking system of p- and n-type materials.

In trying to change how power is generated for billions of people, the details matter. Solar energy is an alluring option, but solar cells are not efficient enough for mass use. To increase efficiency, scientists need to understand and then optimize how the electrons move. By creating a computational model that considers electron motion in three dimensions, scientists made a significant step in that understanding. Previous models only considered two dimensions. The new model produces data points in minutes on a desktop computer. In its first use, it showed electrons moving efficiently using three-dimensional nano networks, called “interdigitated junctions.” Electrons use the junctions to jump from one spot to another, regardless of whether it is beside them or behind them. The model will help in designing solar cells to replace fossil fuels. The Center for Nanostructuring for Efficient Energy Conversion, led by Stanford University, conducted this research.

More Information

Wangperawong A and Bent SF. 2011. Three-Dimensional Nanojunction Device Models for Photovoltaics. Applied Physics Letters 98, 233106(1-3). DOI: 10.1063/1.3595411.

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.