Issue 28, 2023

Towards efficient NFA-based selective near-infrared organic photodetectors: impact of thermal annealing of polymer blends

Abstract

For wavelength-selective photodetection or color discrimination, organic photodetectors (OPDs) can provide significant advantages as solution processability, chemical versatility and functionality. To eliminate the need for commonly used filters, the development of a narrowing approach that simultaneously achieves a selective detection range of less than 50 nm bandwidth and a spectral response greater than 20%, especially for wavelengths designed in the near-infrared, remains a real challenge. Herein, we demonstrate a bulk-heterojunction (BHJ) organic blend exhibiting a filter-free visible-blind near-infrared light responsive characteristic. An indacenodithienothiophene-based non-fullerene acceptor (NFA) of the ITIC family incorporating fluorine atoms, namely ITIC-4F, is mixed with PM6 donor polymer to form ultra-thick active layers in OPDs. A systematic comparison between inverted versus normal architectures was performed using different pairs of hole and electron extraction layer materials. Depending on the thermal annealing temperature of PM6:ITIC-4F blends (from 100 °C up to 200 °C), distinct light responses were observed. While the spectral response of normal structures changes from narrow to broadband with the temperature, inverted structures improve their spectral tuning. A detailed analysis of structure and morphology of blends upon thermal annealing was performed by atomic force microscopy (AFM), contact water angle (CWA) measurement, Raman analysis and 2D grazing-incidence X-ray diffractometry (2D-GIXRD). The transport properties of electrons and holes were further investigated in blends following a Space-Charge-Limited current (SCLC) protocol. We found a marked misbalance between hole and electron mobility values at 200 °C together with highly crystalline films. As a result, the optimized OPD exhibits a high-selective spectral response following the charge collection narrowing (CCN) principle with an external narrowband quantum efficiency of 24.5% and a bandwidth of 42 nm centered at 807 nm. A specific detectivity as high as ∼6 × 1012 Jones is also achieved due to a low dark current density.

Graphical abstract: Towards efficient NFA-based selective near-infrared organic photodetectors: impact of thermal annealing of polymer blends

Supplementary files

Article information

Article type
Paper
Submitted
04 Dzi 2023
Accepted
22 Kho 2023
First published
23 Kho 2023

J. Mater. Chem. C, 2023,11, 9657-9669

Towards efficient NFA-based selective near-infrared organic photodetectors: impact of thermal annealing of polymer blends

Q. Eynaud, Y. A. Avalos Quiroz, T. Koganezawa, R. Sato, N. Yoshimoto, O. Margeat, C. M. Ruiz, J. Ackermann and C. Videlot-Ackermann, J. Mater. Chem. C, 2023, 11, 9657 DOI: 10.1039/D3TC01180A

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