Disaggregation of Self-Assembling Molecules for Efficient Inverted Perovskite Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Physical Chemistry

Background:

• Self-assembling molecules (SAMs) are crucial for efficient hole transport layers in perovskite solar cells (PSCs).
• MeO-2PACz, a common SAM, exhibits self-aggregation in solution due to its amphiphilic nature and hydrogen bonding.
• This aggregation impedes the formation of uniform films, limiting device performance.

Purpose of the Study:

• To investigate the self-aggregation behavior of MeO-2PACz in solution.
• To develop a strategy to suppress SAM aggregation and improve film morphology.
• To enhance the performance and stability of inverted perovskite solar cells (PSCs).

Main Methods:

• Electrospray ionization mass spectrometry (ESI-MS) to identify and quantify SAM oligomers.
• Introduction of a Lewis base (Cl-) and a counterion (PEA+) to disrupt SAM aggregation.
• Scanning transmission electron microscopy (STEM) to analyze film morphology.
• Fabrication and characterization of PSC devices.

Main Results:

• ESI-MS provided direct evidence of MeO-2PACz oligomers (dimers to pentamers).
• The PEACl additive suppressed pentamer formation by over 4-fold and disrupted MeO-2PACz micelles.
• The modified SAM film showed improved molecular packing, enhanced hole mobility, and better energy level alignment.
• PSCs fabricated with the modified SAM achieved 26.3% efficiency and maintained 86.3% of their initial performance after 1200 hours of operation.

Conclusions:

• Self-aggregation of MeO-2PACz is a significant factor limiting PSC performance.
• PEACl effectively mitigates SAM aggregation by disrupting hydrogen bonding and micelle structures.
• The optimized SAM film leads to highly efficient and stable perovskite solar cells, approaching the Shockley-Queisser limit.