Characteristic of polymer photodetectors by using self-assembled monolayer treatment

Abstract

In this thesis we have investigated the characteristics of polymer photodetector fabricated on transparent electrode which is treated by self-assembled molecule (SAM) treatment and we also compared the characteristics of each the devices After the SAM attach on the surface of the transparent electrode the work function of transparent electrode can be modulated due to the molecular dipole moment By choosing different functional group of the SAM the direction and magnitude of the dipole moment can be changed We obtained the result that 1H 1H 2H 2H-Perfluorooctanephosphonic acid (FOPA) is useful for indium-tin oxide (ITO) from all of the SAMs used in this experiment In processing time investigation we obtained the same result between short time treatment and long time treatment (24hr) which is often seen in journal The device with FOPA short time treatment modified on ITO has incident photon to current conversion efficiency (IPCE) 50% and the dark current was 60% reduced compared to non-treatment device Furthermore the detectivity was enhanced by 1 7 times In the treatment of Poly (3 4-ethylendioxythiophene) dope with poly (4-styrenesulfonate) (PEDOT:PSS) which is often used as hole transport layer the dark current was increased by 122 times due to the erosion of the ITO Thus the PEDOT:PSS was not suitable for organic photodetector fabrication We also used the gallium-doped zinc oxide (GZO) substrate for device fabrication and found that the 2 3 4 5 6-Pentafluorobenzylphosphonic acid (FBPA) is useful for GZO The device with modified on GZO has IPCE 47% and dark current was 62% reduced compared to non-treatment device Furthermore the detectivity was enhanced by 1 78 times In the PEDOT:PSS based GZO devices the short circuit current was not increased as in ITO This might mainly due to the increase of the sheet resistance which was caused by hard erosion of the GZO In this thesis instead of PEDOT:PSS by using SAM the photocurrent could be increased and the dark current could be decreased at the same time which results in the improved photodetector detectivity

Date of Award	2015 Jan 26
Original language	English
Supervisor	Wei-Chou Hsu (Supervisor)