Key Takeaways & Executive Findings
- •• • PDPP2F-NDI-N achieves a PCE of 20.44% in ternary OSCs, representing a significant efficiency milestone for solution-processed organic photovoltaics. • • The CIL exhibits exceptional thickness insensitivity, retaining 92.8% of peak PCE at 30 nm thickness, which is critical for roll-to-roll manufacturing where precise thickness control is challenging. • • High electron mobility (1.01 × 10⁻³ cm² V⁻¹ s⁻¹) and electrical conductivity (3.13 × 10⁻³ S m⁻¹) enable efficient charge extraction, reducing resistive losses and improving fill factor. • • Devices demonstrate a T80 lifetime exceeding 1700 hours under photo-thermal aging, indicating superior operational stability essential for commercial deployment.
Abstract
Organic solar cells (OSCs) require cathode interlayers (CILs) that combine high charge transport, defect passivation, and thickness insensitivity for scalable manufacturing. Here, we report the synthesis of a novel A-D-A-A'-type polymer, PDPP2F-NDI-N, via the green and efficient direct arylation polymerization (DArP) method. The multiple electron-deficient units in the backbone confer strong electron-withdrawing character, effective work function modulation, enhanced built-in potential, high crystallinity, and ordered molecular packing. PDPP2F-NDI-N exhibits a high electron mobility of 1.01 × 10⁻³ cm² V⁻¹ s⁻¹ and electrical conductivity of 3.13 × 10⁻³ S m⁻¹, facilitating efficient charge extraction and transport. Its interfacial modification capability suppresses interfacial defects and reduces non-radiative recombination losses. In ternary OSCs, PDPP2F-NDI-N achieves a high power conversion efficiency (PCE) of 20.44%, with outstanding thickness insensitivity retaining 92.8% of peak PCE at a 30 nm CIL thickness, and a T80 lifetime exceeding 1700 hours under photo-thermal aging. This work demonstrates that poly(A-D-A-alt-A') backbone design combined with DArP synthesis provides an effective strategy for developing high-performance, thickness-insensitive, and stable polymeric CILs, advancing efficient, stable, and scalable OSC applications.
1. Introduction
Organic solar cells (OSCs) have emerged as a promising photovoltaic technology due to their low-cost, lightweight, and flexible form factors. However, the cathode interlayer (CIL) – a critical component that facilitates electron extraction and transport – often suffers from thickness sensitivity, where performance degrades significantly with increasing layer thickness. This limitation hampers large-scale manufacturing, as precise thickness control is difficult to achieve in roll-to-roll processes. Conventional CILs based on D-A or A-D-A structures often exhibit poor charge transport and require ultra-thin layers (<10 nm) to maintain efficiency, posing a bottleneck for industrial scalability.
To address this challenge, we introduce a novel A-D-A-A'-type polymer, PDPP2F-NDI-N, synthesized via direct arylation polymerization (DArP), a green and efficient method. The unique backbone design incorporates multiple electron-deficient units, enhancing electron-withdrawing character and promoting ordered molecular packing. This results in high electron mobility and conductivity, enabling efficient charge extraction even at thicker layers. Our work demonstrates that PDPP2F-NDI-N not only achieves a high PCE of 20.44% but also retains 92.8% of its peak performance at a 30 nm thickness, offering a practical solution for scalable OSC fabrication.
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HUANG Haodong, ZHANG Yiqian, KE Jingxin, CHEN Guiting, ZHANG Ming, TIAN Yan, QIN Ze, LI Wanyang, CHEN Hu, ZHAO Baofeng, LIU Feng, LIU Sha (2026). Thickness-Insensitive A-D-A-A' Polymeric Cathode Interlayer for High-Efficiency Organic Solar Cells. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4359-0
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Frequently Asked Questions
What is the impact of the A-D-A-A' backbone on the electronic properties of the polymer compared to conventional D-A or A-D-A structures?
The A-D-A-A' backbone introduces multiple electron-deficient units, which enhances the electron-withdrawing character, leading to deeper work function modulation and increased built-in potential. This results in higher electron mobility (1.01 × 10⁻³ cm² V⁻¹ s⁻¹) and electrical conductivity (3.13 × 10⁻³ S m⁻¹) compared to typical D-A polymers, facilitating more efficient charge extraction and transport.
How does PDPP2F-NDI-N achieve thickness insensitivity, and why is this critical for industrial production?
PDPP2F-NDI-N exhibits high crystallinity and ordered molecular packing, which maintains efficient charge transport even at increased thickness. At 30 nm, it retains 92.8% of its peak PCE, whereas conventional CILs often lose significant efficiency beyond 10 nm. This thickness insensitivity is crucial for roll-to-roll manufacturing, where precise thickness control is challenging, ensuring consistent performance across large-area modules.
What is the operational stability of OSCs using PDPP2F-NDI-N under photo-thermal aging, and how does it compare to industry standards?
Devices with PDPP2F-NDI-N exhibit a T80 lifetime exceeding 1700 hours under photo-thermal aging, meaning they retain 80% of initial PCE after that period. This surpasses typical stability benchmarks for OSCs, which often degrade within a few hundred hours, indicating superior long-term durability suitable for commercial applications.
What are the scalability advantages of using DArP synthesis for PDPP2F-NDI-N compared to traditional Stille or Suzuki coupling?
DArP is a green and efficient method that avoids toxic organotin reagents and reduces synthetic steps, making it more environmentally friendly and cost-effective for large-scale production. The successful synthesis of PDPP2F-NDI-N via DArP demonstrates its potential for industrial-scale manufacturing of high-performance CILs.
How does the interfacial modification capability of PDPP2F-NDI-N reduce non-radiative recombination losses, and what is the resulting impact on device performance?
PDPP2F-NDI-N suppresses interfacial defects and reduces non-radiative recombination, which is evidenced by the high PCE of 20.44% in ternary OSCs. Lower non-radiative losses lead to higher open-circuit voltage and fill factor, contributing to the overall efficiency improvement.
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