Low-Band-Gap Polymer-Based Infrared-to-Visible Upconversion Organic Light-Emitting Diodes with Infrared Sensitivity up to 1.1 μm

All-organic infrared (IR)-to-visible upconversion organic light-emitting diodes (OLEDs) with an IR sensitivity up to 1100 nm were fabricated using a low-band-gap polymer as the organic IR sensitizing layer. A novel low-band-gap (1 eV) polymer, poly 4-(4,8-bis(5-(2-butyloctyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophen-2-yl)-6,7-diethyl-[1,2,5] thiadiazolo[3,4-g]quinoxaline (PBDTT-BTQ), with a strong photoresponse in near-IR wavelengths of 700-1100 nm was first synthesized using a thiadiazolo[3,4]quinoxaline (BTQ) and a thiophene-substituted benzo[1,2-b:4,5-b2-b]dithiophene (BDTT) as the electron-withdrawing and donating building blocks, respectively. The near-IR photodetector was then fabricated for evaluating a PBDTT-BTQ as the IR sensitizing layer. The PBDTT-BTQ IR photodetector showed detectivity greater than 10$^{11}$ Jones in the multispectral region (300-1100 nm) and the maximum detectivity of 3.1× 10$^{11}$ Jones at the wavelength of 1000 nm due to significantly reducing dark current (8.8 × 10$^{-6}$ mA/cm$^2$ at -1 V). Finally, the all-organic IR upconversion OLED with a PBDTT-BTQ IR sensitizer successfully converted invisible near-IR light of 700-1100 nm directly to visible green light with a peak emission wavelength of 520 nm. This is the first report of an all-organic IR-to-visible upconversion OLED with near-IR sensitivity up to 1100 nm.