Date of Award
Doctor of Philosophy (PhD)
This thesis is dedicated to the development of novel and efficient polymer photodetectors based on MEH-PPV conjugated polymers. The polymer-based photodetectors have the advantages of easy processing, low weight, and low cost, and thus are promising candidates for future generations of photodetectors. At present, the quantum efficiency of polymer photodetectors is still low and not comparable to inorganic photodetectors. Therefore, in this thesis we explore ways to enhance the quantum efficiency of polymer photodetectors by using different electron donors, configurations, and implementation of the diffraction optical grating into photodetector structure. We designed, fabricated, and characterized several original types of devices: Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV)/ethyl viologen dibromide (EVD) blended photodetectors, MEH-PPV/PbSe quantum dots (QD) blended photodetectors, MEH-PPV/PCBM blended photodetectors, and MEH-PPV/PCBM blended photodetectors integrated with grating structure.
MEH-PPV/EVD blended photodetectors show a double increase in the external quantum efficiency (EQE) as compared to pure MEH-PPV devices due to ultra fast charge transfer by EVD dication. MEH-PPV/PbSe blended photodetectors demonstrate gain (EQE > 1) for electric fields E ∼ 7 × 10 5 V/cm, which are comparable to inorganic photodetectors. To the best of our knowledge, we were the first to report the gain observed in polymer/nanocrystal photodetectors. The observed photocurrent gain could be attributed to the carrier multiplication in PbSe nanocrystal quantum dots via multiple exciton generation. We also designed a novel MEH-PPV/PCBM photodetector with two blended layers to enhance carrier-transport path. Such a photodetector shows a double increase in the external quantum efficiency compared to the device with only a single blended layer. Lifetime and degradation measurements have shown that the estimated lifetime of devices is from 19–23 days.
Furthermore, we introduce the diffraction grating into the polymer photodetectors to improve light absorption of the devices. Unfortunately, we did not observe any significant enhancement of the external quantum efficiency in MEH-PPV/PCBM photodetectors with grating structures compared to devices without the grating. However, we have laid the initial background for future work, such as thereotical investigation, grating structure optimization, and nano-size patterning on polymer with soft lithography. (Abstract shortened by UMI.)
Qi, Difei, "" (2005). Dissertation. 578.