Mechanical & Materials Engineering, Department of


Date of this Version

Spring 5-25-2014


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering, Under the Supervision of Professor Jinsong Huang. Lincoln, Nebraska: May, 2014

Copyright (c) 2014 Fawen Guo


Organic photodetectors (OPDs) are potentially useful in many applications because of their light weight, flexibility and good form factors. Despite the high detectivities that have been frequently reported for OPDs recently, the application of these OPDs for weak light detection has been rarely demonstrated.

In this thesis, low noise, high gain photodetectors based on organic and ZnO nanoparticles were proposed and demonstrated for highly sensitive UV light detection. The nanocomposite photodetector works in a hybrid mode of photodiode and photoconductor with the transition controlled by the UV light illumination. The nanocomposite detector shows two orders of magnitude higher sensitivity than silicon detectors in the UV range, which is the first time an organic, solution-processed detector has been shown to significantly outperform the inorganic photonic devices.

In the fullerene-based photodetector, the dark-current has been successfully reduced by a cross-linked TPD (C-TPD) buffer layer. The high detectivity of 3.6 × 1011 (Jones) at 370 nm and the wide Linear dynamic range (LDR) of 90 dB, along with a response speed faster than 20 kHz, suggests that the fullerene-based organic photodetectors proposed here can open the way for many potential applications.

The ZnO nanoparticles have been introduced into the C-TPD buffer layer of the fullerene-based photodetector to increase the photoconductive gain and reduce the noise current. The peak external quantum efficiency (EQE) value of approximately 400% and the peak specific detectivity of 6.5 × 1012 Jones at the wavelength of 390 nm, along with the record high LDR of 120 dB, enable the photodetector to be used in wide range of applications such as imaging, communication, and defense. The extremely high sensitivity of the photodetector also makes it particularly attractive for very weak light detection.

Advisor: Jinsong Huang