题 目：Charge transport and interfacial engineering for solution-processed organic optoelectronics
报告人：Yuan Zhang 博士（Center for Polymers and Organic Solids，University of California, Santa Barbara）
Conjugated polymers (CPs) are attractive materials which promise applications in energy conversion devices, large-area displays, and plastic electronics with low-cost fabrication. The functionalities and efficiencies of organic optoelectronics based on CPs are primarily dictated by the charge transport properties. Molecular doping is a powerful strategy in mediating the charge transport in solution-processed CPs. By virtue of p-type doping, the hole mobility of CPs is enhanced with the background hole density controllable by doping levels, allowing for a precise control over the charge injection barrier to the semiconductor. By using the carrier-density dependent mobility model, one obtains a thorough description of the hole transport and temperature dependence in CPs upon doping. In contrast to the hole transport, electron transport in CPs is often trap-limited, giving rise to severe problems in practical device applications. With molecular n-type doping, traps can be deactivated, leading to trap-free and balanced electron and hole transport in diodes. The strategy of doping has been applied for polymer bulk heterojunction photovoltaics (BHJ-PVs), bilayer light-emitting diodes and transistors, showing universal application in realizing improved device performance. In the second part of the talk, charge transport and recombination in organic solar cells based on solution-processed CPs and small molecules (SM) will be briefly discussed. The recombination rate coefficient in SM BHJ-PVs exhibits stronger carrier density dependency than in polymer cells. These results enable in-depth understandings of the carrier losses and the irradiation intensity dependence for BHJ-PVs. In the final part, strategies using DNA layers to tackle charge injection barriers will be discussed. The key functionalities and mechanisms of the DNA layer are related to an interfacial dipole interaction. Latest results in applications of interfacial engineering using DNA layers in organic BHJ-PVs will be discussed.
I was born in Xi’an, China. I received my bachelor and master degree in condensed matter physics at Fudan University, Shanghai. I was awarded my Ph.D. in Physics/Materials Science at the Zernike Institute for Advanced Materials, University of Groningen, The Netherlands in 2010. Since then I came to the Center for Polymers and Organic Solids (CPOS) at the University of California, Santa Barbara in the group of Prof. Thuc-Quyen Nguyen. My current research interest focuses on molecular semiconductors and relevant optoelectronic and energy conversion devices. I am particularly interested in fundamental physical properties of charge carrier transport, injection, recombination and interfaces in these emerging materials and devices, including organic solar cells, thin film transistors and light-detectors. I have also worked on molecular doping of semiconductive polymers and polymeric light-emitting diodes. Before this I had worked on X-ray diffraction imaging technologies using synchrotron radiation for medical applications.