Episode 20: Amino-silane treatment extends perovskite performance

In this podcast episode, MRS Bulletin’s Sophia Chen interviews Yen-Hung Lin of Hong Kong University of Science and Technology about his work to eliminate defects in perovskite solar cells. Lin’s group treated the perovskites with a category of molecules known as amino-silanes, which bind vacancies in the perovskites, preventing recombination of the electrons and holes. The amino-silane treatment retained the device’s performance at 95% power conversion efficiency for more than 1500 hours. This work was published in a recent issue of Science. 

Transcript

SOHPIA CHEN: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Sophia Chen. If you check out the solar panels on your neighbor’s roof or the solar farm out in the blinding Arizona desert, you’ll find most solar panels are made of silicon. But silicon as a material has its drawbacks. It’s expensive to manufacture into solar panels. It makes the panels really bulky, and its efficiency for converting sunlight into energy has plateaued around 26 percent for the last decade. Yen-Hung Lin, a device physicist at Hong Kong University of Science and Technology, is researching an alternative material to silicon for solar panels known as metal-halide perovskites, or perovskites for short.

YEN-HUNG LIN: It can absorb light quite efficiently.

SOHPIA CHEN: Perovskites are a crystal, meaning they’re made of repeating units. They offer a potential advantage over silicon because they could be cheaper to produce, and offer higher efficiency. They can also be made into a thin, flexible material, which makes them less bulky and easier to transport and install. People have also begun creating what’s known as tandem solar cells, where they combine perovskites with silicon. The silicon is best at absorbing the near-infrared wavelengths of sunlight, whereas engineers can tune the perovskites to optimally absorb sunlight in the visible spectrum. The combination allows the solar panel to convert more sunlight into electricity, and experts have recently reported efficiencies of over 34 percent. But perovskites have flaws too, and Lin’s research team is working to make them even better.

YEN-HUNG LIN: The problem is, when we manufacture any kind of material at such a low cost and small budget, we can’t get rid of defects.

SOHPIA CHEN: One common type of defect in perovskites are vacancies, where certain subunits of the perovskite crystal are missing. The defects make the perovskite less efficient and less stable. To understand why, let’s break down what happens when sunlight hits the perovskite. The photons from the sunlight excite electrons in the perovskite from the valence band into the conduction band. This basically separates charges in the material into negative electrons and positive holes. To get the solar panel to produce an electric current, you have to separate the electrons from the holes.

YEN-HUNG LIN: If we don’t take electron and holes out of material, naturally, they will recombine.

SOHPIA CHEN: To make electricity flow through the material, you want to prevent the negative charges from recombining with positive charges. But these defects encourage this undesired recombination.

YEN-HUNG LIN: They are actually acting like a hole, basically to suck this charge carrier in. 

SOHPIA CHEN: Lin’s group found a new way to reduce defects in the perovskite. They treated the perovskites with a category of molecules known as amino-silanes. These molecules bind to those vacancies, preventing recombination. To assess how these molecules improved the perovskite as a solar cell material, the researchers also measured specific electrical properties in the material. When a photon hits the material, it separates the negative electron from a positive hole. This separation creates an internal force that pushes the charges apart, generating electricity. Stronger internal forces mean the solar panel can produce more power. Lin’s team discovered that the force driving these charges was about 90 percent of the maximum level predicted by thermodynamics. In addition, the amino-silane treatment made the entire device more robust to the environment.

YEN-HUNG LIN: They basically form a very strong layer protecting the perovskite underneath.

SOHPIA CHEN: They also tested the amino-silane-treated solar cells’ performance over time. They found that the devices could maintain 95 percent conversion efficiency in open-circuit conditions for more than 1500 hours under full-spectrum simulated sunlight. The devices were also kept at 85°C in relative humidity of 50–60% in ambient air. 

YEN-HUNG LIN: This is the very important assessment for photovoltaic cells’ stability.

SOHPIA CHEN: This work was published in a recent issue of Science. My name is Sophia Chen from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.