Coating boost for tandem perovskite solar cell
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Researchers in China have developed two different ways of protecting perovskite cells to extend the life of tandem solar panels.
Developing large-scale monolithic tandem perovskite/silicon solar cells based on industrial silicon wafers will likely have to adopt double-side textured architecture, given their optical benefits and low manufacturing costs.
Silicon wafers produced by the Czochralski process with micrometer-scale pyramidal structural elements on their surfaces are significantly cheaper than polycrystalline wafers with zone melting. The microtextures from the Czochralski process result in better light capture because they are less reflective than a smooth surface. However, the process of coating these wafers with perovskite results in many defects in the crystal lattice, which affect the electronic properties.
However, the surface engineering strategies that are widely used for perovskites to regulate the interface properties are not directly applicable to micrometric textures.
A team from the Institute of Photovoltaics in the School of Physics and Materials Science at Nanchang University developed a surface passivation with dynamic spray coating (DSC) of a fluorinated thiophenethylammonium material. This provides conformal coverage and reduces problems with a textured surface.
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This DSC treatment enables the tandem cells based on industrial silicon wafers to achieve a certified stabilized power conversion efficiency of 30.89 %. The encapsulated devices also retained over 97 % of their initial performance after 600 hours of continuous use.
In separate research in Hong Kong, researchers have also developed a molecular treatment that significantly enhances the efficiency and durability of perovskite solar cells.
A team at the School of Engineering of the Hong Kong University of Science and Technology (HKUST) identified critical parameters that determine the performance and lifespan of halide perovskites, a next-generation photovoltaic material which has emerged as one of the most promising materials in PV devices for its unique crystal structure.
The team worked with Oxford University and the University of Sheffield in the UK to investigate various approaches for passivation to reduce the number of defects in the perovskite cell and so boost the performance and lifetime of panels.
“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,” said Assistant Professor Yen-Hung Lin of the Department of Electronic and Computer Engineering.
For the first time, the research team showed how different types of amines (primary, secondary, and tertiary) and their combinations can improve perovskite films’ surfaces where many defects form.
“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,” said Lin.
In their solar cell demonstration, the team fabricated devices of medium (0.25 cm²) and large (1 cm²) sizes. The experiment achieved low photovoltage loss across a broad range of bandgaps, maintaining a high voltage output. The cells showed significant 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 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 – among the highest (when factored for the bandgap) and the longest metrics reported to date.
“This treatment is similar to the HMDS (hexamethyldisilazane) priming process widely used in the semiconductor industry,” said 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.”
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