Korean scientists achieve 23.64% efficiency with lift-off perovskite tandem solar cell

Scientists from Korea Institute of Energy Research (KIER) have announced that their new tandem solar cell has achieved a record efficiency of 23.64%. The new cell consists of a top layer of perovskite and a bottom based on copper, indium, gallium and diselenide (CIGS) technology.

Tandem solar cells combine two or more layers of different materials to capture more sunlight and boost efficiency. Each layer absorbs a different solar spectrum, allowing the device to convert more sunlight into electricity than traditional single-layer cells. The design improves performance and energy output.

According to KIER, its technology represents a world record for lightweight, flexible tandem perovskite-CIGS devices. However, an independent third-party entity has not yet confirmed the results.

“The lift-off process developed by the research team involves coating a polyimide layer onto a glass substrate, fabricating the perovskite-CIGS tandem solar cell on top of it, and then separating it from the glass,” KIER said in a statement.

Innovative ‘lift-off’ process

The institute claims the record was achieved using an innovative “lift-off” process, which involves using a rigid glass as a temporary base for the cell. A coat of polyamide (a flexible plastic) is added. The tandem cells are built on top of this layer, with the final flexible solar cell peeling off the glass.

This process differs from more traditional methods that tend to be built directly onto plastic. “Unlike conventional methods that use flexible polyimide film directly as the substrate, this approach utilizes rigid glass as a supporting base, allowing for more stable fabrication of the solar cells. The use of a flat, rigid glass substrate also ensures uniform layer deposition, leading to improved device performance and higher reproducibility,” the statement added.

The new method reportedly avoids issues with flexible cells, such as potassium diffusion from the glass substrate into the CIGS light-absorbing layer. This can be a significant headache for tandem cell producers as it introduces defects into the CIGS absorber.

Durable and efficient

The tandem cell also showed “excellent” durability when tested under standard illumination conditions. “After conducting 100,000 bending cycles, the solar cells maintained 97.7% of their initial efficiency,” KIER said.

“The power-to-weight ratio of the fabricated solar cell is approximately 10 times higher than that of perovskite/silicon tandem solar cells, making it highly promising for applications in fields that require ultralight solar modules, such as building exteriors, vehicles, and aerospace,” Kihwan Kim, one of the authors of the study.

The new cell’s efficiency is impressive but somewhat lower than other record tandem cells developed in recent times. One example is that of the solar cell by King Abdullah University of Science and Technology (KAUST) which reported 33.2% efficiency in April 2023.

China’s JinkoSolar also produced a 33.85% efficient perovskite tandem solar in January this year. However, the new tandem cell stands out not necessarily for its efficiency but for its novel and defect-reduced manufacturing process.

The study has been published in the journal Joule.