A study by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) has claimed it has improved perovskite solar cell (PSC) technology performance by replacing the commonly used fullerene (C₆₀) electron transport layer (ETL) with a newly synthesized ionic salt, commonly referred to as CPMAC.

A study published in the journal Science said that this substitution significantly enhances PSCs’ performance, efficiency, and long-term durability, bringing the technology closer to commercial viability.

Perovskites are materials with a specific crystalline structure known for their exceptional light absorption and semiconductor properties. Despite their lab-scale efficiencies, a persistent challenge has been the long-term stability of perovskite cells, particularly under prolonged exposure to light and elevated temperatures.

Kai Zhu, a senior scientist at NREL, noted that the research focused on improving the chemical composition of the electron transport layer, which plays a crucial role in channeling electrons activated by sunlight through the solar cell.

Although effective, the commonly used C₆₀ fullerene layer has limitations due to its molecular nature. It forms weak interfaces with adjacent layers, resulting in reduced mechanical strength and faster degradation over time, especially under thermal stress.

To resolve this issue, the researchers introduced an ionic salt derived from C₆₀, known as phenylmethanaminium chloride. This compound features a methyleneammonium head group that improves bonding at the ETL interface. Its ionic characteristics promote tighter molecular packing. Together, these features enhance the interfacial mechanical strength by nearly three times compared to conventional.

The report said the PSCs incorporating CPMAC achieved a power conversion efficiency (PCE) of 26.1%, surpassing the 25.5% PCE recorded using standard C₆₀-based layers.

Additionally, stability tests showed only 2% efficiency loss after 2,100 hours of continuous one-sun exposure to 65 degrees Celsius, while C₆₀-based devices showed 5% degradation after 1,500 hours at 85 degrees Celsius.

The technology was also tested on a minimodule consisting of four subcells and a total area of six square centimeters, which achieved a PCE of 23%. These minimodules exhibited less than 9% degradation after 2,200 hours of operation at 55 degrees Celsius.

This advancement also leverages the inverted architecture of PSCs, in which the order of layer deposition is reversed from conventional configurations. Inverted structures are known for their enhanced thermal stability and compatibility with tandem solar cells, which stack multiple layers to capture a broader spectrum of sunlight.

The report claims that this configuration can potentially make the new CPMAC-based approach particularly attractive for next-generation solar modules and commercial-scale production.

In May 2024, NREL proposed enhancing cell and module efficiency to record levels, scale manufacturing, and address reliability and durability issues, as well as figure out the design of hybrid tandem solar modules to better commercialize them.