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Synthetic Approach to Achieve a Thin-Film Red-Selective Polymer Photodiode: Difluorobenzothiadiazole-Based Donor-Acceptor Polymer with Enhanced Space Charge Carriers
- Synthetic Approach to Achieve a Thin-Film Red-Selective Polymer Photodiode: Difluorobenzothiadiazole-Based Donor-Acceptor Polymer with Enhanced Space Charge Carriers
- Kim, Soo-Kwan; Park, Sungmin; Son, Hae Jung; Chung, Dae Sung
- DGIST Authors
- Chung, Dae Sung
- Issue Date
- Macromolecules, 51(20), 8241-8247
- Article Type
- Absorption spectroscopy; Charge carriers; Charge transfer; Film thickness; Heterojunctions; Image enhancement; Photodiodes; Polymers; Tin oxides; Bulk heterojunction (BHJ); Commercial applications; Donor-acceptor polymers; Grazing incidence X-ray diffraction; Intra-molecular charge transfer; Photogenerated charge; Polymer semiconductors; Synthetic strategies; Thin films
- We suggest a synthetic strategy to accelerate charge collection narrowing (CCN) of a polymer photodiode so that a well-defined color selectivity can be realized even with a thin film thickness, which is the most important requirement for commercial application of polymer photodiodes. A new polymer semiconductor POFPhDT2FBT is synthesized by copolymerizing a difluorobenzothiadiazole acceptor with a difluorinated donor moiety. A polymer photodiode with a structure of indium tin oxide/ZnO/POFPhDT2FBT:PC70BM bulk-heterojunction (BHJ) (550 nm)/MoO3/Ag exhibits a high peak detectivity of ∼6 × 1012 jones at 650 nm with a narrow full width at half-maximum <80 nm as well as a low noise equivalent power (4.83 × 10-14 W Hz-0.5), implying that CCN is achieved. This result is valuable as usually a BHJ film with a thickness of 550 nm exhibits a detectivity spectrum similar in shape to the absorption spectrum. We attribute the origin of the thin-film CCN in the POFPhDT2FBT:PC70BM BHJ to a weakened intramolecular charge transfer between the donor and acceptor of POFPhDT2FBT, leading to near-isotropic molecular orientations with a short-range π-π ordering, as confirmed by grazing-incidence X-ray diffraction. In other words, in the case of POFPhDT2FBT, a substantial number of photogenerated charges can remain as space charge carriers, thus enabling the CCN without using a thickness larger than 1 μm. This study shows the possibility of efficient realization of color selectivity of a polymer photodiode even at a film thickness of 550 nm of the active layer, which can contribute to the improvement of the integration of organic image sensors in the near future. Copyright © 2018 American Chemical Society.
- American Chemical Society
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- Department of Energy Science and EngineeringPolymer Energy Materials Lab1. Journal Articles
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