Anion Component Engineering of Spontaneous Perovskite Passivators for Energy Alignment Modulations in Perovskite...

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Alkyl-primary-ammonium-bis(trifluoromethanesulfonyl)imides (RA-TFSIs) are additives for hole-transport materials (HTMs) in perovskite solar cells (PSCs).
• RA cations passivate perovskite defects, while TFSI anions enhance HTM hole mobility.
• The anion component of RA-TFSIs remains underexplored, despite the known effectiveness of bis(fluorosulfonyl)imides being debated.

Purpose of the Study:

• To investigate the role of different bis(fluorosulfonyl)imide anions (FSI, TFSI, PFSI) in RA-TFSIs as HTM additives for PSCs.
• To understand how these anions influence the ionization energy (IE) of HTMs and the overall energy alignment in PSCs.
• To evaluate the impact of these anion variations on the photovoltaic performance and stability of PSCs.

Main Methods:

• Synthesized and characterized n-octylammonium (OA)-bis(fluorosulfonyl)imides (OA-FSI, OA-TFSI, OA-PFSI).
• Incorporated these additives into HTMs for n-i-p structured PSCs.
• Measured ionization energies (IEs) of HTMs and evaluated photovoltaic performance and stability.

Main Results:

• The C-F moieties in bis(fluorosulfonyl)imides correlate with ionization energy; larger moieties (FSI to PFSI) lead to deeper IEs due to expanded electron delocalization.
• FSI-based additives resulted in shallower IEs for HTMs.
• PSCs utilizing FSI-based additives demonstrated improved photovoltaic performance and stability.

Conclusions:

• Anion selection in RA-TFSIs is crucial for tuning HTM ionization energies and optimizing energy level alignment in PSCs.
• FSI-based additives show significant promise for enhancing PSC performance and stability, addressing a key bottleneck in n-i-p structured devices.
• This research offers new insights into HTM additives, paving the way for future advancements in perovskite solar cell technology.