Eliminated Interfacial Side Reactions in Perovskite Solar Cells by Sterically Protected Ammonium Passivation

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Surface passivation with ammonium salts is crucial for reducing defects and improving perovskite solar cell (PSC) performance.
• Conventional ammonium salts can deprotonate at high temperatures, leading to detrimental side reactions with perovskite cations (formamidinium [FA+] and methylammonium [MA+]) and compromising device stability.

Purpose of the Study:

• To investigate the passivation effects of novel cyclohexylammonium iodide derivatives, including cyclohexylammonium iodide (CHAI), methylcyclohexylammonium iodide (MCHAI), and N,N-dimethylcyclohexylammonium iodide (DMCHAI), on PSCs.
• To evaluate the deprotonation resistance and interfacial compatibility of these compounds with perovskite materials.
• To establish design guidelines for developing stable passivation agents for high-performance PSCs.

Main Methods:

• Systematic investigation of CHAI, MCHAI, and DMCHAI as surface passivation agents for PSCs.
• Assessment of the deprotonation tendency of the ammonium salts under thermal stress.
• Fabrication and characterization of PSC devices modified with the investigated passivation agents.
• Evaluation of device performance (power conversion efficiency [PCE], open-circuit voltage [Voc]) and long-term stability under inert atmosphere (N2) and thermal stress (85 °C).

Main Results:

• DMCHAI demonstrated significantly suppressed deprotonation due to its sterically hindered ammonium group, effectively preventing reactions with FA+ at the perovskite interface.
• The champion PSC with DMCHAI modification achieved a high PCE of 26.06% and a Voc of 1.20 V.
• DMCHAI-modified devices retained over 98% of their initial PCE after 7200 hours of operation under N2 and over 86% of their initial efficiency after 550 hours of thermal stress at 85 °C.

Conclusions:

• Deprotonation-resistant ammonium salts are essential for creating thermally stable perovskite interfaces in solar cells.
• DMCHAI represents a promising passivation material for enhancing both the efficiency and long-term operational and thermal stability of PSCs.
• The study provides a rational design strategy for developing advanced passivation materials for next-generation perovskite photovoltaics.