Research Summary

My research interests are generally related to the fabrication and characterization of organic and organic-inorganic hybrid electronic devices. Devices that are of particular interest include solar cells, optical and x-ray image sensors, and field effect transistors.

The focus of my dissertation research is on the development of a bulk heterojunction (BHJ) solar cell with emphasis on morphological control at the nanoscale and correlating changes in solar cell morphology with performance so that we may ultimately improve device stability and efficiency. The effect of interactions between blend components in a three-phase polymer nanocomposite on thin film morphology, polymer crystallization, and device performance is currently under investigation.

Bulk Heterojunction Solar Cells The current state-of-the-art BHJ solar cell is formed by spin casting a polymer nanocomposite thin film comprising a conducting polymer functioning as the electron donor and a semiconducting nanoparticle as the electron acceptor in the device. An optimized quantity of polymer and nanoparticle along with appropriate post-fabrication thermal treatment is required to create bicontinous pathways for the transport of charge carriers to the electrodes. The device structure is presented in Fig. 1.

Figure 1. Bulk heterojunction solar cell structure

 

Photovoltaic power production occurs in the BHJ solar cell via the follow steps: 1) light is absorbed in the polymer producing an exciton (bound electron-hole pair), 2) excitons diffuse through the polymer phase to an interface with an electron acceptor where fast dissociation of the bound charges takes place, and 3) the separated charge carriers (electron and hole) travel to their respective electrodes thereby generating a voltage and current required to supply power to an external load. The band structure of a BHJ solar cell and charge transfer mechanism are depicted in Figs. 2 and 3, respectively.

Figure 2. Band structure for BHJ solar cell

Figure 3. Electron transfer from polymer to nanoparticle when light is absorbed by the polymer

 

Refereed Publications

JA Segui and W Zhao. (2006) Amorphous selenium flat panel detectors for digital mammography: Validation of a NPWE model observer with CDMAM observer performance experiments. Med. Phys. 33, 3711-3722 (2006).

Conference Publications and Abstracts

JA Segui, Y Wang, S Pack, Y Liu, IR Gearba, MH Rafailovich, CT Black. (2009) Nanoparticle confinement in polymer blend thin films for bulk heterojunction solar cell active layers. 2009 American Physical Society March Meeting, Pittsburgh, PA.

JA Segui, IR Gearba, MH Rafailovich, CT Black. (2008) High vacuum annealing of P3HT:PCBM bulk heterojunction solar cells. 2008 Advanced Energy Research Technology Conference, Hauppauge, NY. (2nd place poster)

MM Wronski, A Reznik, JA Rowlands, W Zhao, JA Segui (2008) Development of a flat panel detector with avalanche gain for low-dose x-ray imaging. 2008 54th Annual Meeting of the Canadian Organization of Medical Physicists, Quebec City, Quebec, Canada.

JA Segui and W Zhao. (2007) Development of a TLM to investigate the effect of a resistive interface in digital flat panel x-ray detectors. 2007 32nd Annual IEEE Northeast Bioengineering Conference, Stony Brook, NY, pp 88-89.

JA Segui and W Zhao. (2005) Comprehensive image quality analysis of amorphous selenium based flat panel x-ray detectors for digital mammography. 2005 91st Annual Meeting of the Radiological Society of North America, Chicago, IL.

JA Segui and W Zhao. (2004) Performance of direct and indirect detection methods for digital mammography. In: Pisano, E.D. (ed): IWDM 2004 7th International Workshop on Digital Mammography, Raleigh-Durham, NC.

JA Segui and W Zhao. (2003) An observer study: comparison of direct and indirect detection methods for digital mammography. 2003 Biomedical Engineering Society Annual Meeting. Nashville, TN.