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Transient Dipole Strategy Boosts Highly Oriented Self-Assembled Monolayers for Organic Solar Cells Approaching 21%

Hongyu Mou¹, Yue Yin¹, Haiyang Chen¹

¹Laboratory of Advanced Optoelectronic Materials, Suzhou Key Laboratory of Novel Semiconductor-optoelectronics Materials and Devices, State Key Laboratory of Bioinspired Interfacial Materials Science, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China.

Journal of the American Chemical Society

|June 6, 2025

Summary

A new carbazole-based material (Th-Cz) with enhanced dipole moment improves organic solar cell performance by optimizing molecular arrangement and crystallization dynamics, achieving record power conversion efficiencies.

Area of Science:

Materials Science
Organic Electronics
Photovoltaics

Background:

Self-assembled monolayers (SAMs) based on carbazole, like 2PACz, are crucial for high-performance organic solar cells (OSCs).
However, 2PACz's small dipole moment limits work function modulation and causes interfacial energy loss.
Disordered dipole orientation in 2PACz hinders efficient hole extraction.

Purpose of the Study:

To develop a novel SAM material for OSCs with improved dipole interactions and work function modulation.
To investigate the effect of enhanced dipole moment on molecular arrangement and interfacial energy loss.
To optimize crystallization dynamics and charge transport in the active layer of OSCs.

Main Methods:

Grafting thiophene groups onto carbazole to create a new SAM material (Th-Cz).
Characterizing Th-Cz SAMs for dipole moment, molecular arrangement, and work function.
Analyzing the effect of Th-Cz on active layer crystallization and phase separation.
Fabricating and testing OSCs with Th-Cz as the hole transport layer (HTL).

Main Results:

Th-Cz exhibits a twice-enlarged dipole moment compared to 2PACz due to a transient resonance structure.
This leads to ordered dipole orientation, higher work function, and suppressed interfacial energy loss.
Th-Cz promotes donor crystallization before acceptor, enabling vertical phase separation and balanced charge mobilities.
OSCs with Th-Cz achieved record power conversion efficiencies (PCEs) of 19.34% (PM6:Y6) and 20.91% (D18-Cl:N3:AT-β2O), including flexible devices (19.63%).

Conclusions:

The Th-Cz SAM material significantly enhances OSC performance by improving interfacial properties and active layer morphology.
Enhanced dipole interactions and controlled crystallization dynamics are key to achieving high PCEs.
Th-Cz represents a breakthrough in HTL design for high-efficiency and flexible organic solar cells.

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