Study of inkjet printed photosensitizer for printed metal oxide thin film transistors as photosensors

No Thumbnail Available
Journal Title
Journal ISSN
Volume Title
Kemian tekniikan korkeakoulu | Master's thesis
Date
2020-10-20
Department
Major/Subject
Functional Materials
Mcode
CHEM3025
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Language
en
Pages
84
Series
Abstract
Currently, the thin-film transistor (TFT) is widely used in the field of displays, integrated circuits and X-ray detectors as a key electronic component due to its various advantages. The inkjet-printing method based on the metal salt sol-gel precursors as a potential solution-processed route allows the fabrication of cost-effective, low material waste and eco-friendly semiconductor films. Besides, comparing to the conventional vacuum-based fabrication method which typically requires high processing temperature (generally exceeds 350 °C), the inkjet-printing method can limit the temperature below 300 °C during the whole processing steps. The main advantages for inkjet-printing are additive process, low-material consumption, scalability and potentially lower capital costs etc. Nowadays, some publications have reported novel flexible X-ray detectors on plastic that are based on indium-gallium-zinc oxide (IGZO) TFTs combined with organic photodiodes or amorphous silicon p-i-n photodiodes. However, the flexible and scalable X-ray detector with inkjet-printed TFTs has not been reported yet. Therefore, in this work, we aim to optimize the sensitivity of inkjet-printed metal oxide phototransistors with printed dyes to be usable as the photosensor element for such applications. In this work, two batches of In2O3 based phototransistor samples were fabricated. The first batch studied four different dyes (Rhodamine 6G, Rhodamine B, Phloxine B and Poly-(3-hexylthiophene) (P3HT)) that were printed on top of In2O3 TFTs respectively. The second batch contains two samples printed with Rhodamine 6G and Phloxine B, which were found to be the most promising candidates according to the characterization analysis of the first-batch samples. In addition, the encapsulation of the dye layer with printable polymer (SU-8) was also investigated. The final fabricated sample with Phloxine B from the second batch without SU-8 encapsulation shows higher photosensitivity (PS), responsivity (R), external quantum efficiency (EQE) and detectivity (D) than the sample with Rhodamine 6G from the same batch in the small range of green light (wavelength ~ 565 nm) intensity (0 to 0.18 W/cm2). In the large scale of green light intensity (> 0.18 W/cm2), the situation reverses. To conclude, the inkjet-printed dye-sensitized In2O3 photo-TFT in low processing temperature was fabricated successfully. Although there still exists some challenges such as very low thickness of the inkjet-printed dye layer and unstable electrical properties due to the ambient environment affecting the devices without protective SU-8 encapsulation, the work still shows that it is possible to print the photoactive medium directly on the TFT. Such devices could be applied in flexible, printed X-ray detectors in the future.
Description
Supervisor
Vapaavuori, Jaana
Thesis advisor
Leppäniemi, Jaakko
Keywords
thin film transistor, phototransistor, inkjet printing, indium oxide, dye
Other note
Citation