Chemical Research in Chinese Universities ›› 2024, Vol. 40 ›› Issue (4): 712-721.doi: 10.1007/s40242-024-4103-8

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Optimizing the π-Bridge of Non-fullerene Acceptors to Suppress Dark Current in NIR Organic Photodetectors

SHAO Lin1, HUANG Yijun1, HONG Ling1, XU Zishuo1, YANG Xiye1,2, LIU Chunchen1, HUANG Fei1, CAO Yong1   

  1. 1. State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer Optoelectronic Materials and Devices, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, P. R. China;
    2. Lumidar Technology Co., Ltd., Guangzhou 510530, P. R. China
  • Received:2024-04-22 Online:2024-08-01 Published:2024-07-24
  • Contact: LIU Chunchen,mscliu@scut.edu.cn;YANG Xiye,xyyang@lumidartech.com;HUANG Fei,msfhuang@scut.edu.cn E-mail:mscliu@scut.edu.cn;xyyang@lumidartech.com;msfhuang@scut.edu.cn
  • Supported by:
    This work was supported by the National Natural Science Foundation of China (Nos. U21A6002, 51933003, 52203355), the Basic and Applied Basic Research Foundation of Guangdong Province, China (Nos. 2019B030302007, 2023A1515012293) and the Guangzhou Science and Technology Plan Project, China (No. 2023A04J0970).

Abstract: Recently, the rapid development of non-fullerene acceptors (NFAs) has laid the foundation for performance improvements in near-infrared (NIR) organic photodetectors (OPDs). However, reducing the bandgap of NFAs to achieve strong absorption in the shorter-wave region usually leads to increased dark current density (Jd) and decreased responsivity (R), severely limiting the detectivity (D*) of NIR-OPDs. To date, it remains challenging to manipulate the Jd of NIR-OPDs through rational structure engineering of NFAs. Herein, three NIR-NFAs, namely bis(2-decyltetradecyl)4,4′-(2′,7′-di- tert-butylspiro[cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene]- 2,6-diyl)bis(6-(((Z)-1-(dicyanomethylene)-5,6-difluoro-3-oxo-1,3- dihydro-2H-inden-2-ylidene)methyl)thieno[3,4-b]thiophene-2- carboxylate) (TSIC-4F), bis(2-decyltetradecyl)6,6′-(2′,7′-di-tert- butylspiro[cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene]-2,6- diyl)bis(4-(((Z)-1-(dicyanomethylene)-5,6-difluoro-3-oxo-1,3-dihydro- 2H-inden-2-ylidene)methyl)thieno[3,4-b]thiophene-2-carboxylate) (STIC-4F), and 2,2′-((2Z,2′Z)-(((2′,7′-di-tert-butylspiro[cyclopenta [2,1-b:3,4-b′]dithiophene-4,9′-fluorene]-2,6-diyl)bis(2,3-bis(5-(2- butyloctyl)thiophen-2-yl)thieno[3,4-b]pyrazine-7,5-diyl))bis(metha- neylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1- diylidene))dimalononitrile (TPIC-4F), were designed using the thieno[3,4-b]thiophene (TT) and thieno[3,4-b]pyrazine (TPy) derivatives as the π-bridge. Owing to the intramolecular S-S and S-N interactions, STIC-4F and TPIC-4F exhibited smaller backbone distortions than TSIC-4F. A significantly red-shifted absorption with a peak at 1015 nm was observed in TPIC-4F film, larger than that (ca. 960 nm) for TSIC-4F and STIC-4F films. Moreover, OPDs operating in a photovoltaic mode were successfully fabricated, and TPIC-4F-based OPDs achieved the lowest Jd of 3.18×10‒8 A/cm² at ‒0.1 V. Impressively, although TPIC-4F-based OPDs exhibited the lowest R, higher shot-noise-limited specific detectivity (Dsh*) in 1000—1200 nm could be achieved due to its lowest Jd. This study underscored the effectiveness of optimizing the π-bridge structure of NFAs to suppress Jd, ultimately attaining higher Dsh* in the NIR region.

Key words: π-Bridge, Near-infrared, Non-fullerene acceptor, Dark current, Organic photodetector