Scientists discover new way to boost solar cell efficiency

Researchers from Hong Kong University of Science (HKUST) have developed a molecular treatment that enhances the efficiency and durability of perovskite solar cells. Their research findings could help accelerate the large-scale production of this clean energy.

A key to the solution was the researchers’ successful identification of critical parameters that determine the performance and lifespan of halide perovskites, a next-generation photovoltaic material which shows promise in photovoltaic devices for its unique crystal structure. The research findings have been published in the journal Science.

The researchers investigated various ways of passivation, a chemical process that reduces the number of defects or mitigates their impact in materials, thereby enhancing the performance and longevity of devices comprising these materials. The researchers focused on the ‘amino-silane’ molecular family for passivating perovskite solar cells.

Assistant Professor Lin Yen-Hung said passivation in many forms has been important in improving the efficiency of perovskite solar cells over the last decade. “However, passivation routes that lead to the highest efficiencies often do not substantially improve long-term operational stability,” Lin said.

The researchers showed how different types of amines (primary, secondary and tertiary) and their combinations can improve perovskite films’ surfaces where many defects form. They achieved this using ‘ex situ’ (outside the operating environment) and ‘in situ’ (within the operating environment) methods to observe molecules’ interactions with perovskites. From there, they identified molecules that increase photoluminescence quantum yield (PLQY), known as the quantity of photons emitted during materials excitation, indicating fewer defects and better quality.

“This approach is crucial for the development of tandem solar cells, which combine multiple layers of photoactive materials with different bandgaps. The design maximises the use of the solar spectrum by absorbing different parts of sunlight in each layer, leading to higher overall efficiency,” Lin said.

In their solar cell demonstration, the researchers fabricated devices of medium (0.25 cm²) and large (1 cm²) sizes, achieving low photovoltage loss across a range of bandgaps and maintaining a high voltage output. These devices reached high open-circuit voltages beyond 90% of the thermodynamic limit. Benchmarking against about 1700 sets of data from existing literature showed that their result was among the best reported to date in terms of efficiency in energy conversion.

The study also demonstrated operational stability for amino-silane passivated cells under the International Summit on Organic Solar Cells (ISOS)-L-3 protocol, a standardised testing procedure for solar cells. Approximately 1500 hours into the cell aging process, the maximum power point (MPP) efficiency and power conversion efficiency (PCE) remained at high levels. For the best-passivated cells to decrease to 95% of their initial values, the champion MPP efficiency and the champion PCE were recorded at 19.4% and 20.1% respectively.

Lin said that their treatment process boosts the efficiency and durability of perovskite solar cells and is also compatible with industrial-scale production. “This treatment is similar to the HMDS (hexamethyldisilazane) priming process widely used in the semiconductor industry. Such similarity suggests that our new method can be easily integrated into existing manufacturing processes, making it commercially viable and ready for large-scale application,” Lin said.

Image credit: iStock.com/Bjoern Wylezich