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General Information

OFET and Sensing Applications

The exceptional high mobility of this polymer of up to 10 cm2/Vs [2] via solution-processed techniques, combined with its intrinsic air stability (even during annealing) has made PDPP2T-TT-OD of significant interest for OFET and sensing purposes.

While the highest mobilities require exceptional molecular weights of around 500 kD (and with commensurate solubility issues), high mobilities in the region of 1-3 cm2/Vs can still be achieved with good solution-processing at around 250 kD. As such, we have made a range of molecular weights available to allow for different processing techniques.

In our own tests, we have found that by using simple spin-coating onto an OTS-treated silicon substrate (using our prefabricated test chips), high mobilities comparable to the literature can be achieved  (1-3 cm2/Vs). Further improvements may also be possible with more advanced strain-inducing deposition techniques.

    
  

Photovoltaic Applications

Although shown as a promising hole-mobility polymer for OFETs, when used as the donor material in a bulk heterojunction photovoltaic (with PC70BM as the acceptor), initial efficiencies of 1.6% were achieved for DPP-DTT [3]. The low device metrics were attributed to poor film morphology. However, a higher efficiency of 6.9% was achieved by using thicker film (220 nm) [4].

PDPP2T-TT-OD has also recently been used successfully as an active-layer dopant material in PTB7-based devices [5]. An improvement in device performance was observed, with average efficiencies increasing from 7.6% to 8.3% when the dopant concentration of DPP-DTT was 1 wt%. The use of DPP-DTT as a high-mobility hole-interface layer for perovskite hybrid devices has also been investigated [6].

Synthetic route

DPP-DTT synthesis: DPP-DTT was synthesised by following the procedures described in [2] and [3] (please refer to the following references):

With 2-thiophenecarbonitrile and dimethyl succinate as starting materials in t-amyl alcohol, it gave 3,6-Dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione. Alkylation of 3,6-Dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione with 2-octyldodecylbromide in dimethylformamide afforded 3,6-bis(thiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione. Further bromination gave 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (M1).

Further reaction of M1 with 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene (M2) under Stille coupling conditions gave the target polymer DPP-DTT, which was further purified via Soxhlet extraction with methanol, hexane and then chloroform.

References:

1. A High Mobility P-Type DPP-Thieno[3,2-b]thiophene Copolymer for Organic Thin-Film Transistors, Y. Li et al., Adv. Mater., 22, 4862-4866 (2010)
2. A stable solution-processed polymer semiconductor with record high-mobility for printed transistors, J. Li et al., Nature Scientific Reports, 2, 754, DOI: 10.1038/srep00754 (2012)
3. Synthesis of low bandgap polymer based on 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione for photovoltaic applications, G. Zhang et al., Sol. Energ. Mat. Sol. C., 95, 1168-1173 (2011)
4. Efficient small bandgap polymer solar cells with high fill factors for 300 nm thick films, Li W et al., Adv Mater., 25(23):3182-3186 (2013); doi:10.1002/adma.201300017.
5. Enhanced efficiency of polymer solar cells by adding a high-mobility conjugated polymer, S. Liu et al., Energy Environ. Sci., 8, 1463-1470 (2015)
6. Electro-optics of perovskite solar cells, Q. Lin et al., Nature Photonics, 9, 106-112 (2015)
7. A Vertical Organic Transistor Architecture for Fast Nonvolatile Memory, X. She et al., adv. Mater., 29, 1604769 (2017); DOI: 10.1002/adma.201604769.
8. Solvent-Free Processable and Photo-Patternable Hybrid Gate Dielectric for Flexible Top-Gate Organic Field-Effect Transistors, J. S. Kwon et al., ACS Appl. Mater. Interfaces, 9 (6), 5366–5374 (2017); DOI: 10.1021/acsami.6b14500.