Posted in | Crystallography

Solar-Cell Efficiency Improved by Perovskite Crystals

Scientists from Los Alamos National Laboratory, Rice University and Northwestern University have worked towards enhancing the application of perovskite crystals in the booming solar power industry. This initiative was carried out by modifying their crystal manufacturing technique and producing a new variety of two-dimensional layered perovskite with exceptional strength and increased power transformation capability unlike the material’s earlier conversion efficiency.

Three types of large-area solar cells made out of two-dimensional perovskites. At left, a room-temperature cast film; upper middle is a sample with the problematic band gap, and at right is the hot-cast sample with the best energy performance. (Credit: Los Alamos National Laboratory)

“Crystal orientation has been a puzzle for more than two decades, and this is the first time we’ve been able to flip the crystal in the actual casting process,” said Hsinhan Tsai, a graduate from Rice university and student at Los Alamos. Hsinhan Tsai works with Aditya Mohite, a senior researcher and lead coauthor of a research to be published in the journal Nature. “This is our breakthrough, using our spin-casting technique to create layered crystals whose electrons flow vertically down the material without being blocked, midlayer, by organic cations.”

This study is part of Alamos' mission to carry out multidisciplinary research that will help to intensify the security of energy for the entire nation. The work also involves analyzing different energy sources.

The 2-D material was primarily developed at Northwestern, where Mercouri G. Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry, and Dr. Costas Stoumpos had started to analyze an intriguing 2-D material that aligns its layers perpendicular to the substrate.

The 2-D perovskite opens up a new dimension in perovskite research. It opens new horizons for next-generation stable solar cell devices and new opto-electronic devices such as light-emitting diodes, lasers and sensors. This is a synergy, a very strong synergy between our institutions, the materials design team at Northwestern that designed and prepared high-quality samples of the materials and showed that they are promising, and the Los Alamos team’s excellent skills in making solar cells and optimizing them to high performance.

Mercouri G. Kanatzidis, Professor of Chemistry, Northwestern University

Wanyi Nie, a Los Alamos co-author on the paper, noticed that “the new 2-D perovskite is both more efficient and more stable, both under constant lighting and in exposure to the air, than the existing 3-D organic-inorganic crystals.”

The challenge was to discover something that works in a much enhanced manner than 3-D perovskites, which have extraordinary photophysical properties and power transformation capabilities greater than 20%, but are still plagued by poor quality performance in stress tests of light, heat and humidity.

Earlier study by the Los Alamos team offered awareness on 3-D perovskite performance recovery, given a small timeout in a dark space, and by moving to the stronger 2-D approach, the team obtained improved results.

The 2-D crystals that were studied earlier by the Northwestern team lost power when the organic cations hit the sandwiched space between the layers, knocking the cells down to a 4.73% transformation efficiency because of the out-of-plane arrangement of the crystals. However using the hot casting method to produce the more streamlined, vertically arranged 2-D material appears to have removed the gap. At present the 2-D material has accomplished 12% productivity.

We seek to produce single-crystalline thin-films that will not only be relevant for photovoltaics but also for high efficiency light emitting applications, allowing us to compete with current technologies.

Aditya Mohite, Senior Researcher, Los Alamos National Laboratory

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