Researchers Create Method to Enhance Efficiency of Flexible Tandem Solar Cells

Flexible perovskite/CIGS tandem solar cells developed using the antisolvent-seeding approach (Image by NIMTE)

Chinese researchers have discovered a method to boost both the efficiency and durability of flexible tandem solar cells by improving the adhesion between the top and bottom layers of the cell.

Copper indium gallium selenide (CIGS), a commercial semiconductor, is prized for its highly tunable bandgap, strong light absorption, low sensitivity to temperature, and excellent operational stability. These qualities make it an ideal candidate for the bottom cell in next-generation tandem solar cells.

A flexible perovskite/CIGS tandem solar cell combines a top perovskite layer—known for its effective sunlight-to-electricity conversion—with a CIGS bottom layer. This combination offers great potential for lightweight, high-efficiency photovoltaic applications. However, the rough texture of the CIGS surface complicates the formation of high-quality perovskite layers, hindering the commercial viability of these tandem cells.

In a study published in Nature Energy, a team led by Prof. YE Jichun from the Ningbo Institute of Materials Technology and Engineering (NIMTE), part of the Chinese Academy of Sciences, introduced an innovative antisolvent-seeding technique to improve the growth and performance of perovskite layers on rough surfaces.

Scientists successfully separated the processes of self-assembled monolayer (SAM) adsorption and dissolution while integrating perovskite seeding. They used a high-polarity solvent to prevent SAM clustering during dissolution, and a low-polarity solvent as an antisolvent to encourage the formation of a dense SAM during adsorption. Furthermore, a pre-mixed seed layer enhanced the wettability and crystallinity of the perovskite, ensuring strong adhesion to the substrate.

Using these advancements, the team created a 1.09 cm² flexible monolithic perovskite/CIGS tandem solar cell. Matching the performance of leading rigid solar cells, the device achieved a remarkable stabilized efficiency of 24.6% (certified at 23.8%), ranking among the highest efficiencies reported for flexible thin-film solar cells.

After 320 hours of continuous operation and 3,000 bending cycles with a 1 cm radius, the device maintained over 90% of its initial efficiency, showcasing outstanding mechanical durability and long-term stability.

This breakthrough opens new possibilities for producing affordable, high-performance flexible tandem solar cells and pushes forward the commercialization of tandem solar cell technology.