Boosting solar cell efficiency and durability

This article originally appeared in the September'24 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

This advancement holds promise for accelerating the commercial production of sustainable energy solutions.

Perovskite solar cells, known for their unique crystal structures, have emerged as a leading candidate in photovoltaic (PV) technologies, which convert light into electricity. The HKUST team, led by Assistant Professor Lin Yen-Hung from the Department of Electronic and Computer Engineering and the State Key Laboratory of Advanced Displays and Optoelectronics Technologies, has focused on overcoming the common issue of defects in these materials through innovative passivation techniques.

Passivation, a process that reduces defects in materials, has been critical in improving the efficiency of perovskite solar cells. However, traditional passivation methods have often fallen short in enhancing long-term stability. "Passivation in many forms has been very 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," explained Professor Lin.

The research team's breakthrough came from their exploration of the amino-silane molecular family for passivating perovskite solar cells. They identified the types of amines – primary, secondary, and tertiary – and their combinations that could improve the surfaces of perovskite films, where defects typically form. This was achieved using both ‘ex-situ’ (outside the operational environment) and ‘in-situ’ (within the operational environment) methods to observe the interactions between molecules and perovskites.

The team's approach led to a significant increase in the photoluminescence quantum yield (PLQY), indicating fewer defects and better material quality. This improvement is especially crucial for the development of tandem solar cells, which combine multiple layers of photoactive materials to absorb different parts of the solar spectrum, thereby maximising efficiency.

To demonstrate their findings, the researchers fabricated solar cell devices in medium (0.25cm²) and large (1cm²) sizes. These devices exhibited low photovoltage loss across a broad range of bandgaps while maintaining high voltage output. Remarkably, the devices achieved open-circuit voltages beyond 90% of the thermodynamic limit, positioning their results among the best in the field when benchmarked against approximately 1,700 data sets from existing literature.

The study also highlighted the exceptional operational stability of amino-silane passivated cells. Under the International Summit on Organic Solar Cells (ISOS)-L-3 protocol, a standardised testing procedure, the cells maintained high maximum power point (MPP) efficiency and power conversion efficiency (PCE) even after 1,500 hours of aging. The best-passivated cells showed a champion MPP efficiency of 19.4% and a champion PCE of 20.1%, among the highest reported when considering the bandgap.

"This treatment is similar to the HMDS (hexamethyldisilazane) priming process widely used in the semiconductor industry," noted Professor Lin. "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."

The research team, which included Electronic and Computer Engineering PhD student Cao Xue-Li, Senior Manager of the State Key Laboratory of Advanced Displays and Optoelectronics Technologies Dr. Fion Yeung, and collaborators from Oxford University and the University of Sheffield, underscores the collaborative effort driving this innovation. Their work paves the way for more efficient and durable perovskite solar cells, potentially transforming the landscape of renewable energy.