Innovative Hole-Selective Interlayer Boosts Stability and Efficiency of Perovskite Solar Cells

Researchers from Huaqiao University in Xiamen, Fujian, China, have made a significant advancement in perovskite solar cells (PSCs) by introducing a hole-selective interlayer inspired by proton exchange membrane (PEM) fuel cells.

The researchers pointed out that in PEM fuel cells, the membrane functions as a proton conductor while blocking the diffusion of other chemical species. Drawing from this principle, the researchers applied a similar strategy to PSCs by incorporating a polymeric hole-selective interlayer capable of facilitating hole transport while inhibiting ion diffusion. This approach significantly enhances the stability and efficiency of PSCs.

"The polymer used, PDTBT2T-FTBDT (D18), was selected for its excellent properties as a donor polymer in organic solar cells. The D18 polymer features a fused-ring acceptor unit, dithienothiadiazole (DTBT), which improves π–π stacking, leading to a dense and tightly packed film. Unlike thicker polymeric films that tend to form poorly on perovskite surfaces, the ultrathin D18 layer provides uniform coverage due to its high fluidity in a diluted solution. This dense interlayer blocks ion diffusion while ensuring the structural integrity of the cell during the spin-coating process of Spiro-OMeTAD at room temperature," said the research.

The study also revealed that the D18 layer, with a thickness of approximately 7 nm, effectively blocked ion diffusion while maintaining excellent hole transport. The ion-blocking efficacy of D18 was compared to commonly used polymer hole-transport layers, P3HT and PTAA. Results showed that D18 blocked ion diffusion more effectively than the other two, with the strong π–π interactions in its DTBT backbone resulting in a more compact polymer film. Additionally, tests showed that D18 maintained its ion-blocking capability under thermal stress, ensuring long-term stability.

The optimised PSC architecture—glass/FTO/perovskite/D18/Spiro-OMeTAD/Ag—was spin-coated with D18, which provided a uniform and dense interlayer with high coverage and film quality. The molecular weight of D18 played a role in its solubility and membrane formation, with moderate molecular weight D18 (69 kDa) achieving superior coverage.

As a result of this innovation, the PSCs achieved an impressive efficiency of 26.39 percent (certified 26.17 percent) for a 0.12 cm² device and 25.02 percent for a 1 cm² device. The devices also demonstrated excellent stability, maintaining 95.4 percent of their initial efficiency after 1100 hours under continuous illumination and heat. This remarkable stability represents a significant breakthrough for n-i-p PSCs, which typically face a trade-off between high efficiency and long-term reliability.

In conclusion, this study, published in 'Nature Communications', underscores the potential of polymeric charge-selective interlayers like D18 in enhancing the operational lifetime of perovskite solar cells and modules. This breakthrough paves the way for the commercial application of PSCs, which could play a vital role in the future of renewable energy.