Additive-Stabilized Polymer Electronics Manufacturing (ASPEM)

Lead Research Organisation: University of Cambridge
Department Name: Physics

Abstract

Organic semiconductors have been the subject of focussed research efforts for more than two decades. By investigating a wide range of conjugated polymers as well as molecular materials, molecular structure-property relationships have become understood in detail. This has resulted in a spectacular improvement in materials and device performance: As an example, in the mid 1990's organic semiconductors exhibited field-effect mobilities in transistors of less than 10^-2-10^-3 cm2/Vs, which were at least two orders of magnitude lower than those of industry standard amorphous silicon transistors, that are used in liquid crystal display applications and exhibit mobilities of 1 cm2/Vs. Today state-of-the-art organic transistors reach mobilities of 2-5 cm2/Vs for polymers and 5-15 cm2/Vs for molecular systems. Similarly, the power conversion efficiency of organic solar cells has increased to 14-15% due to availability of improved materials, in particular the development of non-fullerene acceptors. As a result organic semiconductors and conjugated polymers are now an emerging technology in a broad range of applications: Organic light-emitting diodes have become an established display technology for high-end smart phones and TVs. The performance of polymer solar cells cannot compete yet with silicon solar cells for power generation applications, but for indoor energy harvesting organic solar cells are already competitive. Polymer-based OFETs have found niche applications, including flexible e-paper displays. Over the last two years due to the commercial availability of higher mobility materials the outlook for mass market application has improved: More advanced display applications, such as LCD displays, as well as non-display applications, such as X-ray imaging and fingerprint sensing have become technologically feasible and are attracting serious industrial interest and investment.
One of the technology challenges that has, however, not been fully addressed yet is operational reliability: Despite significant progress it would be fair to say that neither OLEDs nor organic solar cells match the impressive reliability of inorganic semiconductor based technologies that in many cases exceed 5-10 years of product lifetime. Also the threshold voltage stability of OFETs during extended periods of operation is inferior to those of oxide or polycrystalline silicon transistors, which exhibit threshold voltage shifts of less than 0.5V during continuous driving over an extended period.
The proposed project is based on a recent technology breakthrough: We have discovered that the operational stability of state-of-the-art high mobility polymer transistors can be dramatically increased by addition of a small molecular additive to the polymer film (Nikolka et al., Nature Materials 16, 356 (2017)). We propose to develop this technique for additive-stabilized polymer (ASP) films into a scalable manufacturing technology that meets the requirements for industrial manufacturing across a range of applications. Our ASP technique has the potential of significantly improving the performance and reliability of conjugated polymers to a level where they can meet similarly demanding reliability requirements as achieved with established inorganic semiconductors.

Planned Impact

The technology developed within the proposed project will provide an industrially scalable manufacturing process for high performance and high stability, multifunctional, molecular additive-stabilized conjugated polymer (ASP) films for a range of applications in electronics, optoelectronics, sensors and energy. It might enable conjugated polymers to reach similar levels of reliability as currently achieved with established inorganic semiconductors.

The project could lead to organic transistors that do not change their characteristics when they are operated for extended periods of time at elevated temperatures. These can be used in light-weight, flexible and robust displays as well as visible and X-ray imaging and fingerprint sensing applications. The project could also enable biological sensors based on conjugated polymers that can be operated more reliably in an aqueous environment without changing their electrical baseline characteristics. These could find applications in a range of healthcare and medical diagnostics applications as well as environmental monitoring. Finally, the project could also lead to achieving a significantly reduced bulk-trap densities in conjugated polymer films. This could allow achieving much higher current densities and lower non-radiative recombination losses and improved device performance in polymer light-emitting diodes and solar cells.

Our proposed manufacturing process for ASP films is highly materials efficient and uses only environmentally benign and naturally abundant materials and will therefore have a positive impact on achieving more sustainable manufacturing of electronic devices.

The project is also likely to have significant scientific impact for the academic community. Because the ASP technique is simple and can be applied to a range of conjugated polymer materials it will enable researchers in the field to study materials with much cleaner transport properties, less affected by extrinsic charge trapping. This could lead not only to an improved scientific understanding of the more intrinsic electronic structure of conjugated polymers, but also to the discovery of further application opportunities for ASP films that are not yet contemplated in this proposal.

Publications

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Chen C (2019) Analysis of Ultrahigh Apparent Mobility in Oxide Field-Effect Transistors. in Advanced science (Weinheim, Baden-Wurttemberg, Germany)

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Jacobs IE (2022) High-Efficiency Ion-Exchange Doping of Conducting Polymers. in Advanced materials (Deerfield Beach, Fla.)

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Nikolka M (2018) Performance Improvements in Conjugated Polymer Devices by Removal of Water-Induced Traps. in Advanced materials (Deerfield Beach, Fla.)

 
Description - Scientific understanding of the mechanism by which molecular additives enhance the operational stability of conjugated polymer transistors; identification of specific molecular additives that meet requirements for industrial manufacturing
- Identification of pathways for improving thermal stability of molecular additives
- Understanding of threshold voltage shift mechanisms for both positive and negative gate voltage stress
- Identification of a mechanism by which an anti-solvent treatment of a conjugated polymer film can lead to significant improvements in positive bias stress stability
Exploitation Route Adoption of molecular additives in industrial manufacturing process. We remain engaged in an active technology transfer process of the technology developed in the project to our industrial partner.
Sectors Electronics

 
Description Ongoing evaluation of stability enhancing molecular additives by industrial partner. Active process of technology transfer to industrial partners involving close co-operation between academic and industrial researchers and monthly joint project meetings. This collaboration will be continued beyond the end of the funding period. A new imaging technique has recently been developed based on results obtained in the original grant (Zhang et al., J. Chem. Phys. 158, 034201 (2023)). This provides a spectroscopic method for monitoring charge transport processes in devices made by our industrial partner. Our industrial partner is supporting a new PhD project that aims to develop this imaging technique into a powerful in-operando monitoring technique.
First Year Of Impact 2022
Sector Electronics
Impact Types Economic

 
Description DTP Case Conversion PhD studentship for Sebastiaan Hoek in collaboration with FlexEnable
Amount £65,177 (GBP)
Organisation FlexEnable Ltd 
Sector Private
Country United Kingdom
Start 01/2024 
End 06/2027
 
Description Studentship funding for Gosia Nguyen from FlexEnable
Amount £27,658 (GBP)
Funding ID RG97230 
Organisation FlexEnable Ltd 
Sector Private
Country United Kingdom
Start 09/2018 
End 03/2022
 
Title Research data supporting "Design of Experiment Optimization of Aligned Polymer Thermoelectrics Doped by Ion-Exchange" 
Description The dxpx files were generated by the software Design-Expert to guide and analyse the design of experiments and study the influence of various rubbing parameters on the polymer chain alignment. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/330495
 
Title Research data supporting "Effects of processing-induced contamination on organic electronic devices" 
Description The repository entry contains research data supporting "Effects of Processing-Induced Contamination on Organic Electronic Devices". The DOI of the publication that cites the data is 10.1002/smtd.202300476. Nuclear Magnetic Resonance (NMR) data The "NMR data - Processed - Topspin" folder contains all the Nuclear Magnetic Resonance (NMR) spectra contained in the paper, as well as additional datasets. The data processing did not induce permanent changes to the data, so the raw data look very similar to the processed data. The "NMR data" project file contains all the NMR data. The individual batches are plotted separately, and also compared to each other to plot the Figures of the paper. The NMR data were processed by TopSpin, and then exported and plotted with Origin. We analyzed the spectra by performing phase correction, apodization with an exponential function (the line broadening weighting factor LB was set to 0.4 Hz), fifth order polynomial baseline correction, and calibration of the chemical shift axis using the CHCl3 peak (7.26 ppm), or one of the C6H5Cl peaks (6.99 ppm). The intensities of the spectra were normalized with respect to either the CHCl3 or C6H5Cl peak of the bottle reference spectrum, or the polymer aromatic signals. Each Figure in the paper mentions the type of peak normalization method that was conducted. Organic field-effect transistor (OFET) data The "Origin project files" folder contains mostly organic field effect transistor (OFET) data (I-V curves). The OFETs were characterized in a nitrogen gas-filled glovebox using an Agilent 4155B semiconductor parameter analyzer with medium power source-meter units and a current resolution of 10 fA. The Origin scripts used to analyze the transistor I-V curves can be found in the OE-FET GitHub repository. Nanomechanical mapping (PeakForce QNM) data The "Nanomechanical mapping (PeakForce QNM) Data" folder contains the raw and processed Peak Force QNM Data, which are shown in Figure 7 of the paper. The folder also contains a short summary that describes the findings. Quartz Crystal Microbalance (QCM) data There is a dataset with Quartz Crystal Microbalance (QCM) data in the "Origin project files" folder. QCM measurements were used to measure the water uptake of polymer films. Video 1 - IDTBT wetting properties modification by the PDMS contaminant from disposable needles The video demonstrates effect of PDMS on the wetting behavior of IDTBT films. It is related to the findings of Figure 6. Initially a clean IDTBT solution in spin-coated, and it dewets. The PDMS contamination is then introduced by briefly dipping a siliconized needle into an IDTBT solution, and swirling it around for 6-7 seconds. The same IDTBT solution then wets the surface and forms a uniform film. Video 2 - Method of redissolving IDTBT films The video demonstrates the method of redissolving IDTBT films, which is one of the five different NMR-based protocols that were used to detect contaminants in the glovebox, as well as leachables from laboratory consumables. The method itself is also described in the Supplementary Information. ~300 µL of deuterated solvent was drawn from the 20 mL vial using a glass pipette. The deuterated solvent was deposited on the polymer film, making sure to stay at least 5 mm away from the edge of the substrate. After the film redissolved, the deuterated solvent was drawn back inside the pipette, and placed in a clean NMR tube. The previous steps were then repeated using a new glass pipette, until the deuterated solvent inside the NMR tube reached the 4.5 cm mark. The filled NMR tube was then labeled and placed in the rack. 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/354389
 
Title Research data supporting "High-mobility, trap-free charge transport in conjugated polymer diodes" 
Description Origin project including all source data used for Figures 1 to 5.The Project is structured in sub-folders, with one folder dedicated to a specfic Figure of the paper. Folder 1 includes SCLC diode characteristics measured for DPP-BTz SCLC diodes with and without additives. Folder 2 includes low-temperature measurements of diodes, extracted activation energies as well as dn/DE values extracted by SCLC-spectroscopy. Folder 3 includes measured diode characteristics of IDT-BT, MEH:PPV and DPP-DTT SCLC diodes, corresponding dn/dE values and PDS spectroscopy data for these materials. The last Folder includes stability measuremtns of DPP-BTz diodes showing the evolution over 10k IV-characteristics. Any additional data from the paper (such as thoese shown in the SI or GIWAXs data) is available on request. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/327981
 
Title Research data supporting Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment 
Description Data to accompany "Improving OFF-State Bias-Stress Stability in High-Mobility Conjugated Polymer Transistors with an Antisolvent Treatment" by Nguyen et al. The zip folder contains subfolders labelled with the figure numbers that can be referred to in the paper. All the subfolders contain raw data either in a .txt or .csv format. The imAFM data from Figure 4 is in .imp (intermodulation) format. Data analysis was carried out using python as described in methods and figure captions of the paper. 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/349080
 
Title Research data supporting The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors 
Description Data to accompany "The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors" by D. Simatos et al., APL Materials 9, 041113 (2021); https://doi.org/10.1063/5.0044785 also available on Apollo (https://www.repository.cam.ac.uk/handle/1810/319841) and arXiv (https://arxiv.org/abs/2104.07089). The zip folder contains raw datasets (.txt and .csv files) of transfer and output curves as well as of positive bias stress (PBS) of OFETs (Organic Field Effect Transistors) fabricated with the semiconducting organic polymers indacenodithiophene-co-benzothiadiazole (C16-IDTBT) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (C14-PBTTT) as well as Cytop-M (CTL-809M) and Cytop-S (CTX809-SP2) gate dielectrics (AGC Inc.). The analysis (.opju file) was carried out in Origin (the data analysis and graphing software from OriginLab). Dielectric thicknesses measured with a profilometer are also included. See the main manuscript for more details. Folder names include information relating to the batch & date of device fabrication, contact geometry (TGBC - top gate bottom contact), type of polymer (IDTBT, N2200), type of dielectric (Cytop-M, Cytop-S), fabrication and testing conditions (nitrogen atmosphere, air exposure or vacuum) and the number of days elapsed since fabrication. In addition, Cryo denotes measurements as a function of temperature and PBS - Positive Bias Stress results. Filenames include information relating to the fabrication batch, contact geometry (TGBC - top gate bottom contact), type of polymer (IDTBT, N2200), type of dielectric (Cytop-M, Cytop-S), fabrication and testing conditions (nitrogen atmosphere, air exposure and vacuum) as well as the number of days elapsed since fabrication, T- transfer curve, O- output curve. PBS filenames also include the time elapsed from the beginning of an experiment and Cryo filenames include the temperature in Kelvin. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/326370
 
Title Research data supporting: High efficiency ion exchange doping of conducting polymers 
Description Data for each figure is included, as well as processing scripts. 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
URL https://www.repository.cam.ac.uk/handle/1810/325168
 
Description Collaboration with industrial partner FlexEnable 
Organisation FlexEnable Ltd
Country United Kingdom 
Sector Private 
PI Contribution Evaluation of molecular additives to improve operational stability of conjugated polymer transistors
Collaborator Contribution Provision of operation stability requirements, test system and test protocols
Impact Stability enhancing molecular additives
Start Year 2018
 
Description  
IP Reference  
Protection Patent application published
Year Protection Granted
Licensed Yes
Impact The invention is currently under development by our licensing partner.