Self-Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency

Area of Science:

• Materials Science
• Organic Electronics
• Renewable Energy

Background:

• Poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) is a common hole-transporting material (HTM) in organic solar cells (OSCs).
• PEDOT:PSS suffers from poor stability due to acidity and hygroscopicity, and its energy levels limit device performance.
• Its infrared absorption and high highest occupied molecular orbital (HOMO) energy level hinder short-circuit current density (Jsc) and open-circuit voltage (Voc) enhancement.

Purpose of the Study:

• To design and synthesize novel asymmetric self-assembled molecules (SAMs) as alternative HTMs for OSCs.
• To address the limitations of PEDOT:PSS in terms of stability and performance.
• To improve photon harvesting, minimize voltage losses, and enhance charge extraction/transport in binary OSCs.

Main Methods:

• Synthesis of two asymmetric SAMs: BrCz and BrBACz.
• Incorporation of BrBACz as an HTM in binary OSCs using PM6:Y6, PM6:eC9, PM6:L8-BO, and D18:eC9 systems.
• Characterization of SAM properties (dipole moment, work function, surface energy) and device performance (efficiency, Jsc, Voc).

Main Results:

• BrBACz exhibits a larger dipole moment, deeper work function, and lower surface energy compared to BrCz.
• PM6:eC9-based binary OSCs with BrBACz achieved a champion power conversion efficiency (PCE) of 19.70%.
• The BrBACz-based device demonstrated a high Jsc of 29.20 mA cm⁻² and Voc of 0.856 V, with 95% efficiency retention after 1,000 hours in ambient air.

Conclusions:

• BrBACz is a highly effective HTM for binary OSCs, surpassing the performance and stability of PEDOT:PSS.
• The developed SAMs offer a promising pathway for creating stable and efficient organic solar cells.
• The record efficiency and long-term stability highlight the potential of BrBACz for commercial applications in organic photovoltaics.