Key Takeaways & Executive Findings
- •• • PSQ-COT:PC61BM OPD achieves a specific detectivity of 1.08 × 10^12 Jones at 1030 nm under zero bias, outperforming the BTP-eC9 counterpart, which is critical for low-light SWIR imaging without external power. • • The absorption onset of PSQ-COT extends to 1.2 μm, enabling SWIR detection beyond the silicon limit, which is essential for applications in biological imaging and optical communication. • • The PSQ-COT:PC61BM device exhibits lower energetic disorder and reduced trap density compared to BTP-eC9, leading to superior performance; this highlights the importance of acceptor selection in optimizing OPD performance. • • Successful integration into a 640 × 512 pixel image array demonstrates the scalability of PSQ-COT for high-resolution SWIR imaging, paving the way for cost-effective, flexible imagers.
Abstract
Short-wavelength infrared (SWIR) organic photodetectors (OPDs) have attracted considerable attention due to their potential to overcome the limitations of inorganic counterparts. However, developing organic semiconductors with strong SWIR detection remains a significant challenge. Herein, we design and synthesize a new conjugated pyrrolic polysquaraine (PSQ-COT) by integrating a pyrrolic squaraine unit with a strong electron-donating moiety, achieving an absorption onset extending to 1.2 μm. To evaluate its detection performance, we fabricated two types of PSQ-COT-based SWIR OPDs with PC61BM and BTP-eC9 as the electron acceptors, respectively. The resulting PSQ-COT:PC61BM OPD exhibited superior detection performance compared with the BTP-eC9 counterpart, achieving an impressive specific detectivity of 1.08 × 10^12 Jones at 1030 nm under zero bias. This enhanced performance is due to the lower degree of energetic disorder and reduced trap density in the PSQ-COT:PC61BM device. Furthermore, we successfully integrated the PSQ-COT:PC61BM OPD into a high-pixel-density image array (640 × 512 pixels), enabling clear matter identification under SWIR light irradiation. This work provides valuable insights into designing high-performance organic semiconductors for SWIR light detection and imaging applications.
1. Introduction
Commercial SWIR photodetectors based on germanium or indium gallium arsenide are structurally rigid, brittle, and require complex fabrication processes, limiting their deployment in portable and flexible applications. Organic photodetectors (OPDs) offer a promising alternative due to their potential for low-cost, flexible, and large-area fabrication, and their thin-film configuration allows seamless integration with CMOS or TFT readout circuits. However, achieving high-performance SWIR OPDs is challenging because designing organic semiconductors with efficient SWIR photoresponse is fundamentally difficult. Traditional strategies such as donor-acceptor conjugation, quinoid resonance, and ion-paired dyes have limitations: synthetic complexity, compromised stability, or poor compatibility with electron acceptors.
This work addresses these bottlenecks by introducing pyrrolic polysquaraine (PSQ-COT), a new conjugated polymer that integrates a pyrrolic squaraine unit with a strong electron-donating moiety. This design achieves an absorption onset extending to 1.2 μm, enabling SWIR detection. By fabricating OPDs with PC61BM and BTP-eC9 acceptors, the study demonstrates that PSQ-COT:PC61BM yields superior detectivity (1.08 × 10^12 Jones at 1030 nm) due to lower energetic disorder and reduced trap density. The successful integration into a 640 × 512 pixel imager further validates its practical utility, offering a viable path toward high-performance, low-cost SWIR imaging.
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Jin He, Zhi Wang, Yaxin He, Qi Xiao, Ming Shao, Zhong'an Li (2026). Pyrrolic Polysquaraine: A Promising Polymer Semiconductor for Short-Wavelength Infrared Organic Photodetector and Imager. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3745-1
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Frequently Asked Questions
What is the specific detectivity of the PSQ-COT:PC61BM OPD at 1030 nm, and how does it compare to the BTP-eC9 counterpart?
The PSQ-COT:PC61BM OPD achieves a specific detectivity of 1.08 × 10^12 Jones at 1030 nm under zero bias, which is superior to the BTP-eC9 counterpart. This is attributed to lower energetic disorder and reduced trap density in the PSQ-COT:PC61BM device.
How does the absorption onset of PSQ-COT enable SWIR detection, and what is its significance?
PSQ-COT exhibits an absorption onset extending to 1.2 μm, which is within the SWIR range (1–3 μm). This enables detection beyond the silicon limit, making it suitable for applications such as biological imaging and optical communication where silicon-based detectors are inadequate.
What are the key factors contributing to the superior performance of PSQ-COT:PC61BM over PSQ-COT:BTP-eC9?
The superior performance is due to lower energetic disorder and reduced trap density in the PSQ-COT:PC61BM device, which reduces non-radiative recombination and dark current, thereby enhancing detectivity.
Can PSQ-COT be integrated into large-area imaging arrays, and what pixel density was achieved?
Yes, PSQ-COT:PC61BM OPD was successfully integrated into a 640 × 512 pixel image array, demonstrating high-pixel-density imaging capability under SWIR light irradiation. This indicates scalability for practical imaging applications.
What are the potential advantages of PSQ-COT-based OPDs over inorganic SWIR detectors in terms of fabrication and cost?
PSQ-COT-based OPDs can be fabricated using solution processing, enabling low-cost, large-area, and flexible devices, unlike inorganic detectors which require complex and rigid fabrication processes. This makes them attractive for portable and wearable applications.
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