Scientists Find New Promising Semiconductor for Solar Cells

This image is a rendition of a one-dimensional, needle-like nanocrystal, such as the one prepared by Vela in collaboration with scientists Emily Smith and Jacob Petrich. Vela's team has prepared a family of highly luminescent perovskite nanocrystals with shape correlated emission. (Credit: Ames Laboratory)

U.S. Department of Energy’s Ames Laboratory scientist Javier Vela describes the results of his recent research on organolead mixed-halide perovskites as “remarkable” and “promising”.

Perovskites are optically active, semiconducting compounds that posses chemical, electronic and light-emitting properties. In recent years, due to their high power conversion potential, low cost and easier processability, lead-halide perovskites have become one of the most sought-after semiconductors for solar cells. These materials increase the power conversion efficiency of the photovoltaics they are made of to more than 20%.

Mixed-halide perovskites were the main focus of Vela’s research. Halides, like bromide, chloride and iodide are negatively charged compounds that are available abundantly. For many reasons, mixed-halide perovskites are preferred over single-halide perovskites.

Vela said that mixed-halide perovskites degrade at a slower pace than single-halide perovskites, as they seem to benefit from moisture and thermal stability. He added that the mixed-halide perovskites can be tweaked to absorb sunlight at certain wavelengths and can be employed in tandem solar cells, light emitting diodes (LEDs) and other applications.

Researchers can manipulate the efficiency and color of these energy conversions devices, by employing these compounds.

Due to his speculation that the internal structure of the mixed-halide perovskites had a hand in these enhancements, Vela who is an associate professor of chemistry at Iowa State University (ISU), collaborated with scientists from ISU and Ames Laboratory with expertise in solid-state nuclear magnetic resonance. NMR, an analytical chemistry method, is used for obtaining chemical, electronic, structural and physical information of complex samples.

“Our basic question was what it is about these materials in terms of their chemistry, composition, and structure that can affect their behavior,” said Vela.

Vela believes that the importance of their discovery is huge and they are only just starting to understand the implication of it.

One obvious implication is that our understanding of the amazing opto-electronic properties of these semiconductors was incomplete. We’re dealing with a compound that is not inherently as simple as people thought.

Javier Vela, Scientist, Ames Laboratory

The details of the study are reported in the paper, “Persistent Dopants and Phase Segregation in Organolead Mixed-Halide Perovskites,” authored by Vela, Bryan A. Rosales, Long Men, Sarah D. Cady, Michael P. Hanrahan, and Aaron J. Rossini; and published online in Chemistry Materials. DOE’s Office of Science supported the endeavor.

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