Scientists build PEDOT:PSS-free all-perovskite tandem solar cell with 29.1% efficiency

Scientists at the Hong Kong University of Science and Technology (HKUST) have developed an all-perovskite tandem solar cell that achieves a record efficiency of 29.1% without using PEDOT:PSS, a common hole transport layer known for stability issues.

The research team replaced PEDOT:PSS with a phenothiazine-functionalized phosphonic acid monolayer called 4PAPT, which improves crystallization, reduces defect density, and enhances interfacial stability. This change led to higher-quality perovskite films and better device performance.

The device architecture involves stacking two perovskite absorbers with complementary bandgaps on indium tin oxide (ITO) electrodes, achieving a monolithic tandem configuration. The bottom cell uses a wide-bandgap perovskite, while the top cell employs a narrow-bandgap perovskite, both optimized for efficiency and stability.

According to Fengzhu Li, the study’s lead author, the new molecular interface strategy not only boosts efficiency but also significantly improves operational stability, with encapsulated devices retaining 90% of their initial efficiency after over 800 hours under simulated sunlight.

Impact of PEDOT:PSS Replacement on Solar Cell Stability and Efficiency

This development represents a significant step towards more durable and efficient perovskite solar cells. Eliminating PEDOT:PSS addresses long-standing stability issues caused by moisture sensitivity and acidity, which can degrade device performance over time.

The achieved 29.1% efficiency surpasses previous records for PEDOT:PSS-free all-perovskite tandem cells, demonstrating the potential for commercial applications where both high efficiency and stability are critical. The molecular monolayer approach offers a pathway to scalable, low-cost manufacturing with improved longevity.

Advances in Perovskite Tandem Solar Cells and Material Challenges

Perovskite solar cells have rapidly advanced, with efficiencies now exceeding 29% in tandem configurations. However, the use of PEDOT:PSS as a hole transport layer has been problematic due to moisture sensitivity and interfacial instability, limiting long-term performance.

Recent research has focused on alternative materials and interface engineering to improve stability and efficiency. The use of self-assembled monolayers, like 4PAPT, has shown promise in controlling crystallization and reducing defect densities, leading to higher-quality films and more stable devices.

This study builds on prior efforts by demonstrating that replacing PEDOT:PSS with molecular monolayers can achieve record efficiencies while enhancing durability, marking a significant milestone in perovskite photovoltaics.

“A major challenge lies at the buried interface of the narrow-bandgap tin-lead perovskite subcell. Replacing PEDOT:PSS with a molecular monolayer enables faster, more stable crystallization and higher device efficiency.”

— Fengzhu Li

Remaining Questions on Long-Term Stability and Scalability

While the initial results are promising, it is still unclear how the new molecular monolayer performs under real-world, long-term operating conditions beyond 800 hours. Additionally, scalability and manufacturing consistency of the monolayer approach require further investigation.

Next Steps Toward Commercial Application and Further Testing

Researchers plan to conduct extended durability testing under outdoor conditions and explore scalable fabrication methods for the molecular monolayer. Further studies will assess the performance of these cells in larger modules and real-world environments to evaluate commercial viability.

Key Questions

How does the new monolayer improve stability compared to PEDOT:PSS?

The phenothiazine-functionalized monolayer offers better interfacial stability, suppresses defect formation, and resists moisture-induced degradation, unlike PEDOT:PSS which is hygroscopic and acidic.

Is this technology ready for commercial use?

Not yet. While efficiency and stability improvements are promising, further testing, scalability assessments, and long-term durability studies are needed before commercial deployment.

Can this approach be applied to other types of perovskite solar cells?

Potentially, yes. The interface engineering strategy using molecular monolayers could be adapted to different perovskite configurations to improve stability and efficiency.

What are the main advantages of eliminating PEDOT:PSS?

Removing PEDOT:PSS reduces moisture sensitivity and interfacial instability, leading to longer-lasting devices with higher efficiency potential.

What challenges remain in implementing this technology at scale?

Challenges include developing scalable deposition processes for the monolayer, ensuring uniformity across large areas, and verifying long-term outdoor stability.

Source: PV Magazine