Skip to main content

Inkjet-Printed organic Photodetectors for Imaging Applications

Final Report Summary - IPPIA (Inkjet-Printed organic Photodetectors for Imaging Applications)

Printing techniques have been used for several hundred years as a method for efficient replication of information on paper. Graphic art industry has benefited from these techniques and consequently mass production tools have been developed to produce big volumes at low cost. The recent development of very diverse solution processable functional materials, with applications ranging from electronics, to chemistry and biology, has envisioned the possibility of a combination of the two approaches in order to mass produce cheap, large-area products capable of advanced functionalities. In the field of electronics there is on one side the drive towards the reduction of manufacturing costs (e.g. active matrix displays and radiofrequency identification tags, RFIDs), on the other the promise to enable applications of devices not currently possible with conventional electronics (bendable displays and detectors, electronic papers, conformable imagers for biomedical applications). Solution processable conjugated organic semiconductors appear to be among the best candidates to enable such applications and, although some scientific and technological challenges have to be faced, their adoption in printed electronic devices has already proved very promising.
IPPIA project was devised to achieve two clear objectives: 1) the development at the host organization, the Istituto Italiano di Tecnologia (IIT), of an internal expertise on inkjet printing techniques of functional materials, especially solution processable organic semiconductors and highly conducting metallic inks, considered as enabling technologies for further development in the field of “plastic electronics”; 2) the development of inkjet printed organic photo-detectors (OPDs) for imaging applications, focusing on the development of OPDs sensitive in the visible spectrum of the light, suitable for integration in an image sensor array. To retain the functionality of the detector in an array, the coupling with a selecting element, a “switch”, had to be realized by developing a suitable organic semiconductor based field-effect transistor (OFETs).

IPPIA project achieved excellent results and moved a critical step towards the development of large-area, lightweight, plastic digital imagers. In this project, the fabrication of plastic digital imagers was approached on the base of digital direct-writing techniques only, namely inkjet printing and laser patterning, on plastic substrates. The project was developed at the Istituto Italiano di Tecnologia (IIT), were a printing lab has been established.
As a result of the research, a high resolution direct-writing technique to fabricate sub-micrometer channels for downscaled OFETs has been developed and published (Organic Electronics 14 (2013) 2249). This approach has been adopted both for printed metallic lines on plastic and for polymer electrodes in order to achieve fully organic, completely direct-written OFETs which are also semitransparent (paper submitted for publication). These FETs have the suitable architecture and footprint to be effectively integrated in a pixel. In particular, with the aim to develop also the addressing electronics for the final imager, we have demonstrated a simple and effective approach for the fabrication of bendable and highly transparent electronic circuits completely relying on carbon based materials, i.e. a highly conducting polymer as electrical contact, a polymer dielectric, and p-/n-type polymer semiconductors, which are all processed with scalable printing techniques at low temperatures on plastic substrates (PEN), combining bendability up to 1 % tensile strain and 90 % transparency. These results have been included in a paper recently submitted for publication.
Moreover, in collaboration with Dr. Dario Natali and Prof. Marco Sampietro of Politecnico di Milano, a breakthrough was achieved in the development of printed organic detectors: a fully inkjet printed organic photodetector with high quantum yield, exceeding 80 % in the visible, has been demonstrated (Advanced Materials 25 (2013) 6829). Such work was reported in a frontispiece cover of the publishing journal to highlight its relevance. A second fundamental step was achieved by demonstrating a fully-printed photodetector based on a narrow band-gap molecule, with a spectral responsivity region extending until 750 nm: the use of small molecules, the synthesis of which can be more readily scaled, opens a vast possibility for spectral tuning. Moreover, we showed that it is possible to fabricate all-organic, semi-transparent detectors where light can be detected from both sides of the device. This result facilitates the integration of the detectors in functional stacks for integration in opto-electronic circuits (Advanced Materials, accepted for publication, DOI: 10.1002/adma.201402918). Semi-transparent, all-printed detectors can pave the way for a cost-effective integration of innovative light sensing elements in future interactive surfaces, flexible displays, and surveillance systems.
Finally, the first all-direct written photodetecting pixels, integrating an OPD and an OFET have been successfully demonstrated. Such pixels enable the fabrication of active detectors arrays, and simple arrays have been fabricated to demonstrate the reliability of the approach.

Results of printed OPDs and pixels define a benchmark in the field of printed opto-electronics. The project overall produced a significant progress in the mastering the technology of ink-jet printing, which constitutes a know-how transversal to many possible applications in the field of organic electronics. The successful integration of the detector and of the switch, which posed several challenges, and its replication in small arrays is exemplary of the high level of controlled achieved: it is now possible to produce a fully integrated pixel on plastic by means of direct writing technologies only. Piezo-electric inkjet printing is a well-developed technology in the graphical arts, therefore processes developed with it would benefit from a faster and easier scale up to industrialization.
By developing a photodecting building block suitable for integration in arrays, IPPIA has set the basis for the realization of printed artificial visual and security vision systems, conformable and light-weight digital scanners and also novel approaches for scientific instrumentations, such as gamma and X-rays detectors (through coupling with a scintillator). Thanks to level of results achieved, technology transfer activities, now being considered, will be pursued following such results.

Throughout the whole project a relevant dissemination activity has been pursued, with several invited talks and seminars at international conferences and institutions and with the publication of review papers on the main topic of the project in leading international journals (D. Natali, M. Caironi "Charge injection in solution-processed field-effect transistors: Physics, Models and Characterization Methods" Advanced Materials 24 (2012) 1357; K.-J. Baeg, M. Binda, D. Natali, M. Caironi, Y.-Y. Noh “Organic Light Detectors: Photodiodes and Phototransistors” Advanced Materials 25 (2013) 4267; K.-J. Baeg, M.Caironi Y.-Y. Noh “Toward Printed Integrated Circuits based on Unipolar or Ambipolar Polymer Semiconductors” Advanced Materials 25 (2013) 4210). A frontispiece was dedicated by Advanced Materials to the development of fully printed detectors (volume 25, 2013). Two invited editorials (Advanced Materials and the Journal of Nanoscience and Nanotechnology, 2013) has been authored by the PI. An IIT press release followed the publication of the Advanced Materials paper in 2013.

The researcher has greatly benefited from this grant, which allowed him to independently develop the line of inkjet printing in IIT, creating also important outcomes in other related projects (e.g. flexible and transparent large-area electronics). He has been managing the printing lab throughout all the project duration and he is now managing a group of 2 postdocs, 6 PhD students, 1 intern, 3 master students, and a technology transfer project employing 3 postdocs and 3 intern. The reseacher applied for the IPPIA grant as a Team Leader, and during the project was appointed as a Tenure Track scientist at IIT, therefore consolidating his integration in the host institution.