2D Phase Purity Determines Charge-Transfer Yield at 3D/2D Lead Halide Perovskite Heterojunctions

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Perovskite solar cells (PSCs) offer high efficiency but suffer from stability issues.
• Functionalizing 3D perovskites with 2D passivation layers is a promising strategy to enhance PSC performance and durability.
• The precise mechanisms behind these improvements are not fully understood.

Purpose of the Study:

• To elucidate the passivation mechanism of 3D perovskite films treated with R-NH3I.
• To investigate the role of the resulting 2D passivation layer in improving perovskite solar cell efficiency and stability.
• To establish design rules for optimizing multidimensional perovskite optoelectronics.

Main Methods:

• Chemical treatment of MAPbI3 perovskite films with R-NH3I.
• Formation and characterization of the 2D (R-NH3)2(MA)PbI4 passivation layer.
• Ultrafast transient absorption spectroscopy to study charge carrier dynamics.
• Analysis of hole injection efficiency into the hole transport layer (HTL).

Main Results:

• R-NH3I reacts with excess PbI2 and unsaturated PbI6 octahedra to form a 2D (R-NH3)2(MA)PbI4 passivation layer.
• A precise 2D layer (n=1) significantly enhances hole injection (>2-fold) to the HTL.
• Excessive 2D layer formation (n>1) impedes hole injection.
• Ultrafast spectroscopy indicates fast hole injection does not occur between the 3D and 2D layers.

Conclusions:

• The study clarifies the passivation mechanism in R-NH3I-treated perovskites.
• Precise control over the 2D passivation layer thickness is critical for optimizing hole injection and device performance.
• These findings provide essential design guidelines for developing stable and efficient multidimensional perovskite solar cells.