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

Researchers from the Hong Kong University of Science and Technology (HKUST) have announced the development of a PEDOT:PSS-free all-perovskite tandem solar cell that achieves a record efficiency of 29.1%. This breakthrough addresses longstanding stability issues associated with PEDOT:PSS, a common hole transport layer, and could significantly advance perovskite solar technology.

The team replaced PEDOT:PSS with a phenothiazine-functionalized phosphonic acid monolayer, known as 4PAPT, which promotes faster and more stable crystallization of the perovskite films. This new interface layer reduces defect densities, enhances interfacial stability, and improves charge transport, leading to higher device efficiency.

The all-perovskite tandem device was constructed with a stacked architecture on indium tin oxide (ITO) electrodes, featuring a wide-bandgap (WBG) bottom cell and a narrow-bandgap (NBG) top cell. The bottom cell used a mixed tin-lead perovskite absorber, while the top cell incorporated the new SAM interface layer. The resulting device achieved 29.1% efficiency, the highest reported for PEDOT:PSS-free configurations.

Encapsulated devices maintained 90% of their initial efficiency after over 800 hours of testing under simulated sunlight at 40°C, indicating improved operational stability compared to traditional designs that use PEDOT:PSS.

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

This development is significant because it demonstrates a viable pathway to improve both the efficiency and durability of perovskite tandem solar cells. By eliminating PEDOT:PSS, which is known for moisture sensitivity and phase segregation issues, the new design addresses key stability concerns that have limited commercial viability. Achieving over 29% efficiency brings perovskite tandem cells closer to commercial competitiveness with silicon-based solar panels, while enhanced stability could reduce long-term operational costs.

Advances in Perovskite Solar Cell Interfaces and Performance

Perovskite solar cells have rapidly advanced, with efficiencies surpassing 25% in single-junction devices and over 28% in tandem configurations. However, the widespread adoption has been hampered by stability issues, particularly related to interface materials like PEDOT:PSS, which can absorb moisture and degrade over time. Recent research has focused on developing alternative interfacial layers that promote better crystallization and stability, with some progress shown in molecularly engineered monolayers. The current breakthrough builds on this trend by demonstrating a high-efficiency, stable tandem device without PEDOT:PSS, a common but problematic component.

“Replacing PEDOT:PSS with a molecularly designed self-assembled monolayer allowed us to control crystallization and improve device stability and efficiency.”

— Fengzhu Li, HKUST

Uncertainties About Long-Term Stability and Scalability

While the devices demonstrated impressive stability over 800 hours, long-term durability beyond this period under real-world conditions remains unconfirmed. Additionally, scalability of the manufacturing process using molecular monolayers like 4PAPT is still under investigation, and potential challenges in large-area fabrication are yet to be addressed.

Next Steps for Commercial Viability and Further Testing

The research team plans to conduct extended stability testing under outdoor conditions and explore scalable manufacturing techniques for the molecular interface layers. Further optimization of device architecture may also lead to even higher efficiencies and commercial readiness within the next few years.

Key Questions

What makes this new solar cell different from previous perovskite devices?

This device replaces the common hole transport layer PEDOT:PSS with a molecular monolayer called 4PAPT, improving stability, crystallization, and efficiency, reaching 29.1%.

Why is removing PEDOT:PSS important?

PEDOT:PSS is moisture-sensitive and can cause instability and phase segregation in perovskite layers. Removing it enhances device durability and performance.

Can this technology be scaled up for commercial production?

Scaling remains a challenge; further research is needed to develop manufacturing processes suitable for large-area devices using molecular monolayers.

How does the efficiency compare to other perovskite tandem cells?

The 29.1% efficiency is currently the highest reported for PEDOT:PSS-free all-perovskite tandem configurations, approaching commercial silicon panel efficiencies.

What are the main advantages of this new design?

Enhanced stability, higher efficiency, and improved interface control, potentially leading to longer-lasting, more reliable perovskite solar panels.

Source: PV Magazine