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Fabrication of organic photo detectors using inkjet technology and its comparison to conventional deposition processes

: Cherian, D.; Mitra, K.Y.; Hartwig, M.; Malinowski, P.E.; Baumann, R.R.


IEEE Sensors Journal 18 (2018), Nr.1, S.94-105
ISSN: 1530-437X
Fraunhofer ENAS ()

The current upscaling of large area electronics is pushing the technological and cost limits of conventional processing and materials. Introduction of new materials, sophisticated device architectures and advanced deposition techniques has made organic photo detector (OPD) attractive for many applications. Spin coated Titanium Oxide (TiOx) has been successfully established as an electron transport layer (ETL) in many optoelectronic devices, including OPDs. In this paper, on one hand OPDs are fabricated with TiOx as ETL deposited by sputtering and electron beam techniques, where the dark current density is reduced by two orders of magnitude up to 10-7 A/cm2 while retaining high photo responsivity. On the other hand, inkjet printing is demonstrated as an alternative additive and digital manufacturing route for the vacuum-free deposition of TiOx and active layer composition of poly(3-hexylthiophene) and [6,6]-phenyl-C60-butyric acid methyl ester (P3HT:PC60BM). OPDs fabricated with inkjet printed TiOx layers showed comparable performance as the state of the art devices fabricated by spin coated TiOx. In addition, OPDs were manufactured using inkjet technology for both the active and ETL layers. Our research proves that there is a significant influence of the deposition technique to the corresponding device performance. The results obtained in terms of figure of merit for OPDs (dark current density of 2.7×10−5 A/cm2, signal to noise ratio of 320, external quantum efficiency of 45% and fabrication yield of 30%-60%) from the developed inkjet printing process shows that further investigation on the ink formulation and optimizations can result into better performing OPDs.