New class of lead-free perovskites for hybrid solar cells

January 22, 2019 // By Nick Flaherty
Researchers at the School of Natural Science at UNIST in South Korea has taken a major step toward the development of a new generation of hybrid solar cells using lead-free perovskites.

A recent study led by Professor Tae-Hyuk Kwon showed that Cs 2SnI6 thecan act as a charge regenerator with dye-sensitized solar cells, enhancing both the overall efficiency and stability. 

Perovskite materials are increasigly popular for solar cells as they can be printed in thin films for flexible and transparent cells, but most of the materials are based on lead iodide. So the 

The team at UNIST examined the charge transfer mechanism of Cs 2SnI6 to determine how its surface state works by using a three electrode system to observe charge transfer. Cyclic voltammetry and Mott-Schottky analyses were also used to probe the surface state of Cs2SnI6, whose potential is related to its bandgap.

The analysis showed that the surface state of the perovskite is highly redox active and can be effectively charged/discharged in the presence of iodide redox mediators. 

"In case of Cs2SnI6, charge transfer occurred through the surface state of Cs2SnI6," says HyeonOh Shin at UNIST. "This will aid in the design of future electronic and energy devices, using Pb-free perovskites."

Based on this strategy, the research team built hybrid solar cells using a Cs 2SnIcharge regenerator for organic dye-sensitized solar cells (DSSCs). Such solar cells generate electric current in the process where the oxidized organic dye returns to its original state.

"Due to a high volume of electrical charges in organic dyes that show high connectivity with the surface state of Cs2SnI6, more electric current were generated," says Byung-Man Kim in the Department of Chemistry at UNIST. "Consequently, Cs 2SnI6 shows efficient charge transfer with a thermodynamically favorable charge acceptor level, achieving a 79% enhancement in the photocurrent density compared with that of a conventional liquid electrolyte."

www.unist.ac.kr

From left above are Kwang Min Kim, Byung Man Kim, HyeonOh Shin, and Professor Tae Hyuk Kwon in the School of Natural Science at UNIST.

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