Creating a More-efficient Perovskite Solar Cell

• Professor Ted Sargent and postdoctoral researcher Somin Park created a more-efficient perovskite solar cell.
• The team devised a strategy termed “co-adsorbent strategy” that employs a co-adsorbent that binds with the organic molecule and can mitigate its tendency to stick together.
• The result is a perovskite cell that is 24.8 percent efficient, bringing the technology closer to common usage and silicon’s efficiency.

Perovskite solar cells could be the future of solar technology. These cells, named after the mineral perovskite, capture the sun’s energy to turn it into power, are very efficient and flexible and come with low production costs. One issue yet to be fully overcome is stability, which still lags behind silicon-based cells.

Recent work from Northwestern Engineering’s Ted Sargent and his colleagues could bridge that gap.

Sargent and members of his lab have developed a solution that combines both efficiency and stability in perovskite solar cells. In perovskite solar cells, the collection layer typically consists of ultrathin organic molecules situated between the perovskites and conductive substrates, the foundation for the combination. Achieving a conformal coating for such a layer necessitates a smooth substrate. However, a textured substrate is often preferred because it can enhance photocurrents through light management. 

In their research, Sargent and his colleagues showed that the grouping of organic molecules during their adsorption on textured substrates leads to incomplete layer coverage. They devised a strategy termed “co-adsorbent strategy” that employs a co-adsorbent that binds with the organic molecule and can mitigate its tendency to stick together.

The method produced results in a more predictable molecule distribution, achieving a perovskite solar cell that is 24.8 percent efficient, the high-water mark for this method. The investigators hope this can accelerate the adoption of perovskite technology, contributing to the ongoing energy transition.

“The primary barrier to the commercialization of perovskite solar cells is their long-term stability,” said Sargent, professor of electrical and computer engineering at the McCormick School of Engineering, professor of chemistry at Northwestern’s Weinberg College of Arts and Sciences, and co-executive director of the Paula M. Trienens Institute for Sustainability and Energy. “While an inverted architecture generally offers superior stability compared to a standard architecture device, its efficiency requires enhancement. We offer a facile method to boost the efficiency of inverted devices. The improved deposition of ultrathin organic coatings will also find broad applications in other optoelectronic devices, such as light-emitting diodes and photodetectors.”

A paper describing the findings, titled “Low-Loss Contacts on Textured Substrates for Inverted Perovskite Solar Cells,” was published October 23 in the academic journal Nature. Sargent was the paper’s corresponding author, while Somin Park, a postdoctoral researcher in Sargent’s lab, was the paper’s first author.

This research built on prior work by Sargent’s group into perovskite solar cells. Earlier this year, Sargent and Park were part of a team that created a perovskite solar cell that can stand up to high temperatures for more than 1,500 hours — a key milestone as this emerging technology moves closer to commercial application. 

Following this work, the researchers plan to subject their device to outdoor testing, comparing lab stability with real-life stability, and developing a reliable physical model to relate their behaviors. They will then work on scaling up the devices from lab-sized small cells to modules that can be installed and utilized in a solar plant.

These newer cells, however, represent a step forward as Sargent and collaborators continue their research.

“We anticipate that our insights into the adsorption mechanisms of molecules on textured substrates can be easily applied to other perovskite solar cell architectures, like multi-junction devices, advancing both efficiency and stability forward,” Park said.