Research Center to Explore New Class of Semiconductor

Lead-halide perovskite solar cells have seen rapid gains in efficiency and stability over the past few years. And many solar energy researchers have come to see this technology—based on a type of organic-inorganic crystal—as one of today’s most promising emerging solar energy technologies.

However, the typical lead-halide perovskites are only a narrow class of a broad group of materials known as hybrid organic-inorganic semiconductors—or HOIS. Consequently, a new Energy Frontier Research Center, funded by the U.S. Department of Energy (DOE) and led by a team at DOE’s National Renewable Energy Laboratory, will bring together an interdisciplinary team to study these semiconductors.

The goal of the new Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) is to better understand and control the emergent phenomena of spin, charge, and light/matter interactions in HOIS, potentially unlocking new energy technologies.

“Although there are enormous efforts worldwide on developing lead-halide perovskites for photovoltaic applications, our center will focus on the larger class of hybrid organic-inorganic semiconductors with broader energy applications in mind,” said Matthew Beard, lead principal investigator for CHOISE. “We want to develop a deeper understanding leading to control of their fundamental properties in order to transcend the initial focus on photovoltaic research.”

Semiconductor technology has revolutionized our world over the past decades. A deep understanding of this technology has enabled computers, LEDs, and various other power electronics. However, HOIS are significantly more complex than many traditional types of semiconductors.

The crystal lattice structure of HOIS incorporates both organic and inorganic components. These components can act individually and in concert in a range of ways due to their varied chemistries. They can also interact as extended systems that display unusual, so-called emergent behaviors that cannot be predicted based on a sum of the individual parts.

For example, in all other organic and inorganic semiconductors, light striking the semiconductor generates charge carriers that relax within a few hundred femtoseconds. In HOIS, the charge carriers can relax up to a thousand times more slowly—a beneficial characteristic. Currently, the exact physical and chemical mechanisms that underlie many of these unusual properties are not well understood.

Many HOIS crystals and films can be fabricated from solutions at or near room temperature, rather than from high-temperature melts or gas-phase epitaxy. So the composition and structure of their crystal lattices are controlled by solution-phase chemistry. This synthetic control over crystal formation should allow researchers to tailor optical and electronic properties of HOIS. 

In particular, the CHOISE team hopes to learn how to exert precise control over the spin, charge, and light/matter interactions of HOIS materials. If successful, this control of fundamental properties will provide crucial insights to aid in the rational design and synthesis of a broad library of HOIS for energy applications.

Because of the complex interplay of organic and inorganic components in HOIS, researchers from various disciplines must work together to better understand the interaction. CHOISE will bring together world-leading experts across synthetic organic and inorganic chemistry, physics, material science, and photochemistry. In fact, many members of the CHOISE team have already made major discoveries in the field of HOIS.

DOE’s Energy Frontier Research Center program is designed to bring together researchers from multiple disciplines and institutions and combine them into highly productive teams. CHOISE’s researchers come from a range of institutions—Duke University, University of North Carolina-Chapel Hill, University of Utah, DOE’s SLAC National Accelerator Laboratory, University of Toledo, San Diego State University, and the University of Chicago—with DOE’s National Renewable Energy Laboratory as the lead organization.

“We believe that we have a tremendous opportunity to develop foundational knowledge that will drive a new paradigm in semiconductor science and technology,” said Beard.