Physicist Seung-Hun Lee and chemical engineer Joshua J. Choi show off an example of hybrid organic-inorganic perovskite (HOIP).
Photo by Dan Addison, University Communications

Only about 1% of the world’s energy production currently comes through solar cell technology. That’s because solar cells are expensive to produce and are susceptible to efficiency reductions over time.

For this reason, scientists continue to seek new solar cell materials that will overcome these deficiencies. One of the most promising is a class of materials discovered in 2009: hybrid organic-inorganic perovskites (HOIPs).

These extremely lightweight and flexible materials are inexpensive to produce compared to traditional silicon-based cells. At 22% (or better) efficiency at converting energy from the sun into electricity, they are approaching the 25% energy-producing efficiency of silicon cells. HOIPs also can be applied to surfaces as a thin spray-on or paint-on coating, making them usable in a variety of settings and applications, from roofs to vehicles to backpacks.

However, HOIPs are somewhat unstable, degrading in quality fairly rapidly and susceptible to temperature changes. The atomic structures of the materials change when the temperature changes, and only particular types of molecular structures have the ability to capture energy from the sun and convert it into electricity.

Scientists and engineers at the University of Virginia, with colleagues at the National Institute of Standards and Technology (NIST) Center for Neutron Research, the Oak Ridge National Laboratory, and Cornell University, have made new inroads on understanding the fundamental physics behind how these cells work in various structural phase transitions.

They detail their findings in a paper published in the journal Science Advances, identifying how organic molecules in the structures play a crucial role in how the phase transitions occur.

By microscopically probing the materials using neutron-scattering experiments and computer simulations, they have discovered ways to expand the stable range for the desired solar cell structure during temperature changes. The results could potentially revolutionize solar cell technology by speeding the process of designing materials that are efficient and stable across a wide range of temperatures while remaining inexpensive to produce in large quantities.

“This opens new opportunities to unlock the full potential of the HOIP-based solar cells in real applications,” says UVA Physicist Seung-Hun Lee, who led the study with his colleague, UVA chemical engineer Joshua J. Choi.

The physical insight at the molecular level allows the researchers to stabilize the properties of the material in various structural phases.

“The improved stability across wider ranges of temperatures will enable application of HOIP solar cells even in extreme conditions such as on spacecraft and aircraft that operate in colder environments,” Choi says.

HOIPs may have particular applicability for situations where lightweight solar cell material is needed, such as to power electronic equipment for infantry on the battlefield, for backpackers, for autonomous or remotely controlled high-altitude drones, and for satellites.

Lee and Choi believe that HOIPs, or some variation of these materials, will be available someday in the near future as inexpensive inks that could be printed onto rolls of paper or plastic and then used as flexible lightweight solar cells for a range of personal electronics uses.

University of Virginia