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Autumn 2015

Digging Deep into Data to Capture the Sun

How perovskite solar cells are streamlining the search for new solar cell materials

Lauren Garten

This is a schematic of the crystal structure of the perovskite structured methyl-ammonium lead halide materials

Increasing global energy demands make it necessary to quickly find efficient and cost-effective alternative energy sources. Solar energy offers a clean and progressively more efficient alternative. Currently, the process of developing materials for solar cells is slow and lengthy; this makes finding ways to expedite the discovery and development of new solar materials a priority. The Center for Next Generation Materials by Design (CNGMD) is expediting the search with new high-throughput computational search methods. Here, researchers are examining the lessons learned from the perovskite solar cell success to find new disruptive solar technologies.

A recent investigation of a particular crystal structure called perovskite has shown promise for solar cell applications. The rapid efficiency gains that have occurred in perovskite solar cells the last few years outpace the development of any solar technologies to date. Current reports place the efficiency near 20 percent (up from 5 percent just 6 years ago), which is competitive with current commercially available solar cells. Inspired by the breakthroughs, researchers at the CNGMD are using perovskite materials to identify guidelines to quickly find novel or unexplored solar materials through data mining. The traditional approach of material experimentation is slow, but computer techniques could take years off the standard trial-and-error approach, reducing it to only months of searching.

Based on these perovskite materials, scientists have identified an important characteristic to use as search criteria: defect tolerance. An example of a defect could be a missing or misplaced atom in the structure. Defect tolerance could indicate that not many defects were formed; it could also indicate that the defects that are present do not have a detrimental effect on material's properties such as the conversion of sunlight to electricity.

So what influences a material’s defect tolerance? Computer models of the perovskite materials show that the defect tolerance is likely because of the chemical bonding in this material. The bonds formed in the material affect how intrinsic defects will interact with the charges being generated by the absorption of light. The nature of the chemical bonds in the perovskite material generates distinct features that can be used to narrow the search for other interesting solar cell materials.

These features include specific electrical properties. The first to be highlighted is mobility – the ability of electrons to move through the material. The second is relative static permittivity, which relates to how distortable the material is under the influence of an electric field. Perovskite solar materials have a higher permittivity, which "protects" charge carriers from defects, reducing scattering, and increasing mobility. These material properties can be used as guidelines to swiftly identify other materials that should emulate the defect tolerance of the perovskite system.

The researchers then used these guidelines to search through the Materials Project, an open Internet database with computed information on known and predicted materials. Additional constraints were placed to remove toxic elements, such as lead, from the search. This high throughput screening of more than 27,000 materials identified nine families of materials that could be promising candidates for optoelectronic applications. Bismuth-sulfur-bromine is just one example of the unexplored materials discovered by this method. Computer modeling was again used to verify the data mining process and provide a comparison with the electrical and optoelectrical properties of the perovskite materials.

As computational and experimental databases continue to develop, large-scale data mining for functional materials has become a reality. And now what could have taken years has been reduced to months. The methodology from this study can easily be applied in energy generation or computational materials development. But, most important, we now have a way to identify promising solar materials faster so we can be better prepared for our future energy needs.

More Information

Brandt RE, V Stevanovic, DS Ginley, and T Buonassisi. 2015. "Identifying Defect-Tolerant Semiconductors with High Minority-Carrier Lifetimes: Beyond Hybrid Lead Halide Perovskites." MRS Communications 5:265-275. DOI: 10.1557/mrc.2015.26

Acknowledgments

This work was supported as part of the Center for Next Generation Materials by Design (CMGMD), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. R.E.B. acknowledges a National Science Foundation GRFP Graduate Research fellowship program.

About the author(s):

Data Mining Could Shave Years off Solar Cell Research

Database searches identify defect-tolerant materials that could lead to mainstream solar energy

Scientists are using computers to find the next generation of materials for solar cells.

Trial and error is a slow, expensive way to discover the materials needed to revolutionize solar cells. While databases on materials exist, scientists were unsure as to the most important material feature. Using the experimental data from perovskites, which have quickly become an effective choice for solar cells, scientists prioritized the features needed for new materials. They put defect tolerance as number one. The team then searched a database of more than 27,000 materials and found 9 groups of promising materials. Next, they will sort their findings based on other vital properties. This work could accelerate solar cell research and assist in other discoveries. The Center for Next Generation Materials by Design performed the study; the National Renewable Energy Laboratory leads the center.

More Information

Brandt RE, V Stevanovic, DS Ginley, and T Buonassisi. 2015. "Identifying Defect-Tolerant Semiconductors with High Minority-Carrier Lifetimes: Beyond Hybrid Lead Halide Perovskites." MRS Communications 5:265-275. DOI: 10.1557/mrc.2015.26

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.