Scientists at the National University of Singapore (NUS) have demonstrated a perovskite–organic tandem solar cell with a certified world-record power conversion efficiency of 26.4 per cent over a 1 cm² active area — making it the highest-performing device of its kind to date. This milestone is driven by a newly designed narrow-bandgap organic absorber that significantly enhances near-infrared (NIR) photon harvesting, a long-standing bottleneck in thin-film tandem solar cells.

This latest research breakthrough was achieved under the leadership of Assistant Professor HOU Yi, who is a Presidential Young Professor in the Department of Chemical and Biomolecular Engineering under the College of Design and Engineering at NUS and leads the Perovskite-based Multijunction Solar Cells Group at the Solar Energy Research Institute of Singapore (SERIS) at NUS.

The NUS research team published their groundbreaking work in the prestigious scientific journal Nature on 25 June 2025.

Unlocking the promise of tandem solar cells

Perovskite and organic semiconductors both offer widely tunable bandgaps, enabling tandem cells to approach very high theoretical efficiencies. “Thanks to their light weight and flexible form factor, perovskite–organic tandem solar cells are ideally suited to power applications that are run directly on devices such as drones, wearable electronics, smart fabrics and other AI-enabled devices,” said Asst Prof Hou.

However, the absence of efficient NIR thin-film absorbers – which help to capture sunlight in the NIR region more efficiently and hence improving the overall efficiency of tandem cells - has kept perovskite–organic tandem cells lagging behind alternative designs.

Harnessing the near-infrared

To overcome this challenge, Asst Prof Hou and his team developed an asymmetric organic acceptor with an extended conjugation structure, enabling absorption deep into the NIR region while maintaining a sufficient driving force for efficient charge separation and promoting ordered molecular packing. Ultrafast spectroscopy and device physics analyses confirmed that this design achieves high free charge carrier collection with minimal energy loss.

Building on the organic subcell’s performance, the researchers stacked it beneath a high-efficiency perovskite top cell, interfacing the two layers with a transparent conducting oxide (TCO)-based interconnector.

The newly designed tandem cell achieved a power conversion efficiency of 27.5 per cent on 0.05-cm² samples and 26.7 per cent on 1-cm² devices, with the 26.4 per cent result independently certified. These findings mark the highest certified performance to date among perovskite–organic, perovskite–CIGS, and single-junction perovskite cells at comparable size.

“With efficiencies poised to exceed 30 per cent, these flexible films are ideal for roll-to-roll production and seamless integration onto curved or fabric substrates — think self-powered health patches that harvest sunlight to run onboard sensors, or smart textiles that monitor biometrics without the need for bulky batteries,” noted Asst Prof Hou.

Next step

In the next phase of their research, the NUS team will focus on enhancing real-world operational stability and advancing towards pilot-line manufacturing - crucial steps in bringing flexible, high-performance solar technology to market.