Restricting Li⁺ Migration via Mixed Hole Transporting Materials Strategy for Stable tBP-Free Perovskite Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (tBP) are crucial dopants for high-efficiency perovskite solar cells (PSCs).
• However, Li+ ion migration and tBP volatility compromise the long-term stability of PSCs.

Purpose of the Study:

• To develop a stable, tBP-free hole transporting material (HTM) for enhanced PSC performance and longevity.
• To investigate the role of a novel terpyridine-based HTM (TPy-CzDPA) in stabilizing Li-TFSI dopants.

Main Methods:

• A novel terpyridine-based HTM (TPy-CzDPA) was synthesized and mixed with Li-TFSI and spiro-OMeTAD.
• The coordination between TPy-CzDPA and Li+ was analyzed to understand ion stabilization.
• Hole mobility and device performance were measured for the developed HTM blends.
• Long-term stability tests under thermal stress and humidity were conducted on fabricated PSCs.

Main Results:

• TPy-CzDPA effectively coordinates with Li+, restricting Li+ migration and preventing hydrolysis.
• The mixed HTMs exhibited enhanced thermal stability and a higher hole mobility (2.53 × 10-4 cm2 v-1 s-1).
• PSCs achieved a champion power conversion efficiency (PCE) of 22.13%.
• Devices retained 90% of initial efficiency after 528 h at 80°C and showed only a 14% PCE drop after 4800 h under 30-40% RH.

Conclusions:

• TPy-CzDPA serves as an effective and stable alternative to tBP in PSCs.
• The developed strategy significantly improves the operational stability and efficiency of perovskite solar cells.
• This work presents a promising approach for fabricating durable and high-performance tBP-free PSCs.