Chinese scientists build ‘ultra-stable’ polymer solar cell with 19.1% efficiency

A group of researchers from Wuhan University of Technology in China has fabricated a polymer solar cell that can achieve a 19.1% efficiency while maintaining remarable stability levels. 

Polymer solar cells are a subset of organic solar cells where the active light-absorbing material is specifically a conjugated polymer.

“Polymer solar cells employing polymeric electron donors and acceptors demonstrate superior mechanical property and thermal stability compared to their small molecular counterparts,” the research's corresponding author, Wei Li, told pv magazine. “However, the long-conjugated backbones of polymeric semiconductors are prone to self-entangle into large and disordered aggregates, consequent to inferior PCE as well as quicker degradation during operation. We found that the incorporation of linearly packed small molecule acceptor can help to disentangle the polymeric chains, transforming the disorder molecular packing into ordered stacking.

“This simple strategy simultaneously creates efficient pathways for charge transport whilst reducing free volume among the photoactive layer,” added co-author, Tao Wang. “The resulting devices retain 97% of the initial efficiency after 2,000 hours of operation in air, with extrapolated lifetime exceeding 100,000 hours. This work elucidates how molecular and morphological structures of organic semiconductors govern the device lifetime, and provides a practical pathway toward commercialization of flexible organic photovoltaics.”

In the study “Ultra-stable polymer solar cells with T₉₇ lifetime over 2,000 h in air,” published in Matter, the researhers explained that they used polymeric acceptors (PMAs) instead of other types of polymers because they offer a distinctive balance between structural stability and photovoltaic performance.

Unlike small-molecule acceptors (SMAs), polymeric macromolecular acceptors (PMAs) are constructed from long conjugated backbone chains. This macromolecular architecture reduces free volume in the active layer and limits large-scale molecular motion. As a result, PMA-based devices exhibit superior thermal and morphological stability, translating into significantly longer operational lifetimes.

Mechanical properties provide another key advantage of PMAs. Compared with small-molecule systems, polymeric acceptors form more robust and flexible films. Chain entanglement enhances both mechanical durability and film-forming ability, which is particularly valuable for flexible and large-area solar cells. By contrast, small molecules tend to crystallize excessively or undergo phase separation over time, causing morphological instability and device degradation.

However, PMAs also have drawbacks. Their long chains can self-entangle into disordered aggregates in the solid state, reducing structural order in the active layer. This disorder increases charge carrier recombination, typically resulting in lower power conversion efficiencies compared with state-of-the-art SMA-based devices. Consequently, a trade-off exists between efficiency and stability.

The research team addressed this challenge by introducing a small fraction of carefully selected small-molecule acceptor into the PMA matrix. This approach reportedly improves molecular packing and structural order, while mitigating recombination losses and preserving the intrinsic thermal stability of the polymer system.

The solar cell was fabricated on an indium tin oxide (ITO) substrate with a molybdenum trioxide (MoO₃) hole transport layer (HTL), a large-bandgap conjugated polymer donor PM6, an active layer based on poly(methyl acrylate) (PMA), a buckminsterfullerene (C60) electron transport layer (ETL), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact.

Under standard illumination, the device achieved a power conversion efficiency of 19.1%, an open-circuit voltage of 0.941 V, a short-circuit current density of 26.3 mA/cm², and a fill factor of 77.3%. Absorption spectroscopy measurements indicated that the cell’s lifetime exceeded 2,000 hours in air.

“In conclusion, ultra-stable polymeric solar cells were achieved through dedicated design of the photoactive and charge transport layers,” the researchers stated.

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