Researchers Find Low-Toxic Materials for Roll-to-Roll Perovskite Solar Cells

Organic semiconductor materials are the top choices for R2R PV cells


Researchers from Swansea University have found that introducing compatible hole-transport materials (HTLs) between perovskite and carbon can significantly enhance the performance of perovskite solar cells (PSC).

PSCs offer a potential solution for efficient and economical renewable energy production. However, their widespread adoption is hindered by the lack of scalable fabrication methods.

Roll-to-roll processing is a promising approach for large-scale manufacturing, particularly when incorporating carbon electrodes. This brings benefits such as cost-effectiveness and stability.

The advancement holds the potential to enable cost-effective and high-throughput fabrication of PSCs, making them suitable for emerging applications such as building-integrated photovoltaics.

The researchers evaluated the efficiency, stability, and scalability of four interlayers (Spiro-MeOTAD, PTAA, PEDOT, and P3HT) in printed devices.

The findings indicate that Spiro-MeOTAD and PTAA were incompatible with the carbon electrode, while PEDOT and P3HT showed promising results.

Also, P3HT may be a preferable option for scaling up production when comparing P3HT and PEDOT in terms of stability, toxicity, and cost.

The researchers said these insights offer valuable guidance for optimizing the performance of perovskite solar cells in large-scale manufacturing through roll-to-roll printing.

Results and Discussion

Spiro-MeOTAD, widely used in spin-coated devices, performed poorly when combined with carbon electrodes due to weak charge transfer. This was attributed to compatibility issues between spiro and the carbon ink, resulting in altered chemical composition and reduced charge extraction efficiency.

PTAA, known for its hole-transport properties, also exhibited compatibility issues with carbon electrodes, leading to suboptimal device performance.

In contrast, P3HT, despite being insoluble in commonly used toxic solvents, showed promise in low-toxic solvents like O-xylene, offering compatibility with R2R coating processes and demonstrating efficient charge transfer with carbon electrodes.

PEDOT, previously shown to perform well in carbon-based devices, continued to exhibit high compatibility and stability, making it a viable choice for R2R PSC fabrication.

Comparative analysis of the four HTLs revealed that P3HT and PEDOT displayed minimal changes in surface roughness after solvent washing, indicating compatibility with the coating process.

Both materials demonstrated high charge-selecting ability and improved device performance compared to spiro and PTAA. Stability tests showed promising results for both P3HT and PEDOT, with P3HT exhibiting superior long-term stability under high humidity conditions.

Transitioning to R2R coating, P3HT solutions at concentrations below 10 mg ml−1 in O-xylene demonstrated successful coating and maintained device performance comparable to spin-coated devices. PEDOT also performed well in R2R-coated devices, highlighting its suitability for large-scale production.

The study evaluated these materials on rigid ITO glass substrates and extended to fully R2R coating of flexible PET ITO substrates with a resistivity of ~50 Ω sq−1.

In the R2R setup, devices incorporating PEDOT achieved a respectable PCE of 10.6%, while those with P3HT reached a PCE of 9.8%.

Moreover, tests conducted under different conditions showcased long-term stability for unencapsulated perovskite solar cells featuring carbon electrodes and these two HTL materials.

After 90 days, the unencapsulated devices with P3HT and PEDOT retained 85% and 75% of their initial PCE, respectively, with P3HT offering superior stability.

Both PEDOT and P3HT demonstrated compatibility with 2-methyl anisole, the solvent used for the carbon ink, in fully R2R PSCs. However, opting for P3HT over PEDOT presents several advantages, including higher humidity stability, use of a less toxic solvent, and lower cost.

Last March, researchers at UK-based Swansea University established a low-cost and scalable carbon ink formulation with the potential for large-scale manufacturing of perovskite solar cells.

Early this year, a research team at the University of Michigan created tandem cells by combining silicon-based semiconductors with perovskites to make the cells last longer.