Shortwave infrared-absorbing squaraine dyes for all-organic optical upconversion devices

Karen Strassel; Wei-Hsu Hu; Sonja Osbild; Daniele Padula; Daniel Rentsch; Sergii Yakunin; Yevhen Shynkarenko; Maksym Kovalenko; Frank Nüesch; Roland Hany; Michael Bauer

doi:10.1080/14686996.2021.1891842

Shortwave infrared-absorbing squaraine dyes for all-organic optical upconversion devices

Sci Technol Adv Mater. 2021 Apr 13;22(1):194-204. doi: 10.1080/14686996.2021.1891842.

Authors

Karen Strassel^{1

2}, Wei-Hsu Hu^{1

3}, Sonja Osbild¹, Daniele Padula⁴, Daniel Rentsch¹, Sergii Yakunin⁵, Yevhen Shynkarenko^{5

6}, Maksym Kovalenko^{5

6}, Frank Nüesch^{1

3}, Roland Hany¹, Michael Bauer¹

Affiliations

¹ Laboratory for Functional Polymers, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
² Ecole Polytechnique Fédérale de Lausanne, EPFL, Institute of Chemical Sciences and Engineering, Lausanne, Switzerland.
³ Ecole Polytechnique Fédérale de Lausanne, EPFL, Institute of Materials Science and Engineering, Lausanne, Switzerland.
⁴ Dipartimento di Biotecnologie, Chimica e Farmacia, Università di Siena, Siena, Italy.
⁵ Department of Chemistry and Applied Biosciences, Laboratory of Inorganic Chemistry, Zürich, Switzerland.
⁶ Laboratory for Thin Films and Photovoltaics, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.

Abstract

Shortwave infrared (SWIR) optical sensing and imaging are essential to an increasing number of next-generation applications in communications, process control or medical imaging. An all-organic SWIR upconversion device (OUC) consists of an organic SWIR sensitive photodetector (PD) and an organic light-emitting diode (OLED), connected in series. OUCs directly convert SWIR to visible photons, which potentially provides a low-cost alternative to the current inorganic compound-based SWIR imaging technology. For OUC applications, only few organic materials have been reported with peak absorption past 1000 nm and simultaneous small absorption in the visible. Here, we synthesized a series of thermally stable high-extinction coefficient donor-substituted benz[cd]indole-capped SWIR squaraine dyes. First, we coupled the phenyl-, carbazole-, and thienyl-substituted benz[cd]indoles with squaric acid (to obtain the SQ dye family). We then combined these donors with the dicyanomethylene-substituted squaraine acceptor unit, to obtain the dicyanomethylene-functionalized squaraine DCSQ family. In the solid state, the absorbance of all dyes extended considerably beyond 1100 nm. For the carbazole- and thienyl-substituted DCSQ dyes, even the peak absorptions in solution were in the SWIR, at 1008 nm and 1014 nm. We fabricated DCSQ PDs with an external photon-to-current efficiency over 30%. We then combined the PD with a fluorescent OLED and fabricated long-term stable OUCs with peak sensitivity at 1020 nm, extending to beyond 1200 nm. Our OUCs are characterized by a very low dark luminance (<10^-2 cd m^-2 at below 6 V) in the absence of SWIR light, and a low turn-on voltage of 2 V when SWIR light is present.

Keywords: 201 Electronics / Semiconductor / TCOs; 204 Optics / Optical applications; 301 Chemical syntheses / processing; 306 Thin film / Coatings; 40 Optical, magnetic and electronic device materials; 501 Chemical analyses; Squaraine dye; organic photodetector; organic upconverter; shortwave infrared.

Grants and funding

This work was supported by the Italian Ministry of Education, University, and Research (MIUR) [Rita Levi Montalcini grant]; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung [206021_150638/1,IZBRZ2_186261,IZRJZ2_164179].