A new approach to manufacturing perovskite solar cells, designed by the US National Renewable Energy Laboratory (NREL), has solved key problems facing the technology and yielded devices with high efficiency and stability.

Creating highly stable and efficient perovskites based on a rich mixture of bromine and iodine is considered critical for the development of tandem solar cells. The two elements, however, tend to separate when exposed to light and heat and therefore limit the voltage and stability of a solar cell.

An illustration of a modern perovskite high performance solar cell module. (Image by Audio und werbung via Shutterstock)

The newly developed approach flips the typical perovskite cell. Using the inverted architectural structure, the approach relies on what is known as ‘gas quenching’, where a flow of nitrogen is blown onto the chemicals. This stops the bromine and iodine separating, resulting in a perovskite film with improved structural and optoelectronic properties. The gas quenching process, when applied to high-bromine-content perovskite chemicals, forces the crystals to grow together, tightly packed from top to bottom like a single grain, and significantly reduces the number of defects.

In the tandem solar cell, the narrow-bandgap layer is deposited on top of the wide-bandgap layer. The difference in bandgaps allows for more of the solar spectrum to be captured and converted into electricity. The new approach produced a wide-bandgap solar cell with an efficiency of greater than 20% and 1.33V photovoltage and little change in the efficiency over 1,100 hours of continuous operation at a high temperature. With this new approach, an all-perovskite tandem cell obtained an efficiency of 27.1% with a high photovoltage of 2.2V and good operational stability.

“This new growth approach can significantly suppress the phase segregation,” Kai Zhu, a senior scientist at NREL and principal investigator on the project, said in a statement.