Chemical hardness engineering synchronizes crystallization in perovskite tandems

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Chemistry

Background:

• All-perovskite tandem solar cells face challenges due to asynchronous crystallization in multicomponent perovskites.
• This leads to vertical compositional gradients, structural inhomogeneity, and increased non-radiative recombination, stemming from mismatched coordination and crystallization kinetics of mixed halides and cations (Pb²⁺/Sn²⁺).

Purpose of the Study:

• To develop a generalizable additive design strategy to synchronize nucleation and crystal growth in both wide- and narrow-bandgap perovskites.
• To improve the performance and stability of all-perovskite tandem solar cells by addressing crystallization challenges.

Main Methods:

• Employed hard-soft acid-base (HSAB) principles to design additives that synchronize perovskite crystallization.
• Utilized borderline-base difluoro(oxalato)borate and hard-base tetrafluoroborate to selectively coordinate wide- and narrow-bandgap perovskite precursors.
• Conducted in situ optical and structural characterization to monitor nucleation and crystal growth.

Main Results:

• Achieved vertically uniform perovskite films with reduced defect densities and suppressed ion migration.
• Demonstrated monolithic two-terminal tandem solar cells with a certified efficiency of 30.3% and improved open-circuit voltage (2.16 V) and fill factor (85.2%).
• Showcased flexible tandem solar cells with a certified efficiency of 28.2% and maintained 92% of initial efficiency after 1,000 hours of operation.

Conclusions:

• Established chemical hardness matching as a universal principle for controlling crystallization in diverse perovskite systems.
• The additive strategy effectively synchronizes nucleation and crystal growth, leading to enhanced performance and stability in all-perovskite tandem solar cells.
• This work paves the way for more efficient and durable perovskite solar cell technologies.