The power conversion efficiency (PCE) of all-organic solar cells has been doubled, thanks to the development of novel organic electrodes that can be fabricated using a moderate, more practical process.
Example of damage to the lower layer of a solar cell disposal formed from multilayer films when fabricating electrodes using a solution process. Image Credit: Kanazawa University
As global efforts to combat climate change intensify, the demand for solar energy continues to grow. Yet, silicon-based solar panels, the most widely used today, contain a variety of hazardous substances, making their disposal and recycling environmentally taxing and costly.
Similar concerns surround next-generation film-type solar cells, such as perovskite-based devices, which also incorporate potentially harmful materials like lead compounds and metal oxides.
In search of an eco-friendlier alternative, scientists have been working on film-type solar cells made entirely from carbon-based materials, known as all-organic solar cells. Free of hazardous metals, these cells can be safely incinerated like regular plastics, significantly reducing environmental impact and lowering disposal costs.
However, despite these advantages, current all-organic solar cells have achieved a relatively low PCE—typically around 4 %—far below the efficiencies of conventional silicon (>27 %) and perovskite (>26 %) solar cells. To make all-organic cells viable, major performance improvements have been necessary.
Now, a collaborative team led by Associate Professor Masahiro Nakano from the Institute of Science and Engineering, Faculty of Chemistry, Kanazawa University, working with researchers from REIKO Co., Ltd. (President Junichi Iwai) and Queen's University at Kingston, Canada, has achieved a major breakthrough. They successfully developed all-organic solar cells with the highest reported efficiency to date, more than double that of previous designs.
Two major obstacles had long limited the performance of all-organic solar cells. First was the limited availability of highly conductive, transparent organic electrode materials suitable for film-type cells. Although some high-conductivity organic materials existed, their production typically required strong acids, bases, or high-temperature annealing (>150 °C), processes that could damage delicate organic films and substrates.
To address this, the research team developed a new transparent electrode based on the conductive polymer PEDOT:PSS. This electrode can be fabricated at a much lower temperature (80 °C) without the need for harsh chemicals and offers sufficient conductivity (sheet resistance: <70 Ω/sq.) for use in film-type solar cells.
The second challenge involved stacking multiple layers within the device without damaging the underlying organic films—a common issue during solution-based fabrication processes.
To overcome this, the team introduced a "lamination method of carbon nanotube electrode." Instead of forming electrodes directly on sensitive layers, they prepared them separately on barrier films and then laminated them onto the device, minimizing damage to the bottom layers during assembly.
By combining the new PEDOT:PSS-based electrode and the innovative lamination method, the researchers achieved a significant leap in performance, developing all-organic solar cells with a PCE of 8.7 %—more than double the previous maximum of 4.0 %.
This advancement marks a critical step toward the practical application of high-performance all-organic solar cells. Looking ahead, these cells offer exciting possibilities for use in environmentally sensitive areas, such as farmland and wearable electronics. Their lightweight and flexible design also makes them ideal for installations where traditional rigid panels are not suitable.
The research team is now focused on further boosting efficiency by improving the conductivity of organic electrodes.
Journal Reference:
Hashida, K., et al. (2025) Unlocking High‐Performance in All‐Organic Solar Cells by the Development of Organic Electrodes with No Acid and High‐Temperature Treatment and the Effective Preparation Thereof on Organic Multilayer Films. Advanced Functional Materials. doi.org/10.1002/adfm.202419813.