Proceedings of MATSUS Spring 2024 Conference (MATSUS24)
DOI: https://doi.org/10.29363/nanoge.matsus.2024.175
Publication date: 18th December 2023
Near-infrared organic photodetectors (OPDs) experienced a fast growth in recent years owing to their advantages over traditional inorganic photodetectors. By fine-tuning the optical bandgap of the organic material, OPDs can be engineered for high and specific light detection. In particular, the advent of non-fullerene acceptors (NFAs), with tunable energy levels, allowed OPDs with light detection in the near-infrared (NIR) region.
Analyzing the structures of reported NFAs, many of the best performing contain thiophene-based fused aromatics within the donor core. A strategy to shift the absorption windows is to replace the thiophene moiety with selenophene. Selenophene has lower aromatic stabilization energy than thiophene and will increase the quinoidal character of the material.
Until now, few fused selenophene containing NFAs containing straight chain alkyl groups have been reported. The replacement of the alkyl aryl groups with straight chain alkyl groups will change the solid-state microstructure of thiophene-based NFAs and then enhance the power conversion efficiency (PCE). In this work, we report the first NFA containing a fused indacenodiselenophene with octyl sidechains at the bridgehead positions. This is the direct selenophene analogue of the previously indacenodithiophene acceptor known as IDIC, which has been widely reported in the OPV community.
Herein we show that the selenophene analogue IDSe exhibits a red-shifted absorption compared to the thiophene analogue IDIC, and when paired with a suitable wide band gap donor PTQ10, organic photodetector devices using a bulk heterojunction configuration have an ultralow dark current density (Jd) of 1.65×10-9 A cm-2 at -2V and a specific detectivity (D*) of 1012 Jones at -2V bias. With a combination of optoelectronic measurements, transient analyses and morphological investigations based on GIWAXS measurements, we attributed the low Jd of the PTQ10:IDSe blend to the higher and more balanced carrier mobilities compared to the thiophene benchmark. In addition, we fabricated large-area OPDs (5x5 cm substrates) using doctor blade coating in air and obtained extraordinarily low dark current, indicating its ability to be large-scaled processed in the future.
The authors thank the Engineering and Physics Science Research Council (EPSRC) (EP/T028513/1 and EP/V057839/1), the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2020-CRG8-4095 and ORFS-2023-OFP-5544, NSG Pilkington, the M2A funding from the European Social Fund through the Welsh Government. We are grateful to the SPECIFIC Innovation and Knowledge Centre (EP/N020863/1).
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