Title:  Organic Semiconductor Bulk Heterojunction Diodes with Low Dark Current for Photovoltaic Photodetection and Scintillator-free Ionizing Radiation Detection Applications

Committee:

Dr. Bernard Kippelen, ECE, Chair , Advisor

Dr. Linda Milor, ECE

Dr. Samuel Graham, ME

Dr. Azad Naeemi, ECE

Dr. Albert Frazier, ECE

Abstract: 

Solid-state organic semiconductor-based photovoltaics (OPV) are an emerging technology being developed to generate clean and sustainable electricity. This technology holds the promise of being inexpensive to be mass-produced and deployed in light weight, flexible and shatter-proof form factors.

In this dissertation, progress to enhance the environmental stability of OPV is presented. Novel OPV cell architectures are investigated in which the commonly used but particularly unstable calcium electrode is replaced by a polymeric substituent that leads to the formation of an efficient electron-collecting electrode in conjunction with various air stable metals including silver and gold. The performance of the novel calcium-free OPV is found to be comparable to the reference cells that contain calcium electrodes.

Secondly, OPV-inspired design rules for organic photodetectors are presented. The conventional approach in developing organic photodetectors focuses on the importance of so-called charge blocking layers at the electrodes that minimize recombination and reduce the dark leakage current that defines the sensitivity of the detector. This work highlights the significance of the interaction between the components of the photoactive layer in defining the limit of sensitivity of the photodetector, rather than the use of charge blocking layers. Thereafter, by optimizing the choice of semiconductor materials, the morphology and thickness of the photoactive layer, and the charge collecting-electrodes, organic semiconductor-based photodetectors that exhibited comparable performance to silicon photodetectors are demonstrated with high specific detectivity (D* >1014 Jones) at visible and near infrared wavelengths. Novel applications enabled by the detectors are also explored, such as scintillator-free detectors for ionizing radiation.