The research team identified critical parameters determining the performance and lifespan of halide perovskites, a next-generation photovoltaic material known for its unique crystal structure. Their findings were published in Science.
Led by Assistant Professor LIN Yen-Hung of the Department of Electronic and Computer Engineering and the State Key Laboratory of Advanced Displays and Optoelectronics Technologies, the team explored various passivation methods. Passivation is a chemical process that reduces or mitigates defects in materials, enhancing device performance and longevity. They focused on the "amino-silane" molecular family for passivating perovskite solar cells.
"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," Prof. Lin explained.
The team showed, for the first time, how different types of amines (primary, secondary, and tertiary) and their combinations can improve perovskite films' surfaces where many defects form. They used both "ex-situ" (outside the operating environment) and "in-situ" (within the operating environment) methods to observe molecules' interactions with perovskites. This led to the identification of molecules that substantially increase photoluminescence quantum yield (PLQY), 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 maximizes the use of the solar spectrum by absorbing different parts of sunlight in each layer, leading to higher overall efficiency," Prof. Lin elaborated.
In their solar cell demonstration, the team fabricated devices of medium (0.25 cm) and large (1 cm) sizes. The experiment achieved low photovoltage loss across a broad range of bandgaps, maintaining a high voltage output. These devices reached high open-circuit voltages beyond 90% of the thermodynamic limit. Benchmarking against about 1,700 sets of data from existing literature showed their results were among the best reported to date in terms of energy conversion efficiency.
The study also demonstrated remarkable operational stability for amino-silane passivated cells under the International Summit on Organic Solar Cells (ISOS)-L-3 protocol, a standardized testing procedure for solar cells. Approximately 1,500 hours into the cell aging process, the maximum power point (MPP) efficiency and power conversion efficiency (PCE) remained high. The champion MPP efficiency and PCE were recorded at 19.4% and 20.1% respectively, among the highest and longest metrics reported to date.
Prof. Lin emphasized 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," he said. "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 team 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, along with collaborators from Oxford University and the University of Sheffield.
Research Report:Bandgap-universal passivation enables stable perovskite solar cells with low photovoltage loss
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