Guangyong Li Assistant Professor, Electrical and Computer Engineering


Fax: 412-624-8003
506 Benedum hall
Pittsburgh, PA


Development of High-Resolution Scanning Kelvin Probe Force Microscopy

The most efficient organic photovoltaic cells (OPVCs) today are made from blending conjugated polymers (donors) and fullerene molecules (acceptors) together to form bulk heterojunctions (BHJs) at nanoscale.  The nanoscale morphology of the blend, largely affected by processing conditions, determines the charge generation and transport, and hence dictates the device performance. LiDespite the importance of morphology, the exact correlations among morphology and performance and processing conditions are still not completely clear due to the lack of in situ characterization tools. Scanning probe microscopes (SPMs) are versatile tools to characterize organic photovoltaic cells in ambient.  However, several problems limit the application of SPMs in characterization of organic photovoltaics such as unable to differentiate the donor and acceptor domains in nanoscale and unable to observe the in situ morphological changes during annealing. Therefore, to better understand the physics of organic photovoltaic devices and to find out how the processing conditions affect the nanoscale morphology and hence the device performance, there is a pressing need to develop in situ characterization tools, with which the morphological changes can be monitored in real time with high resolution.  The objective of this research is to find the quantitative correlation among nanoscale morphology and device performance and processing conditions by developing an in situ characterization system that can perform highly sensitive kelvin probe force microscopic study on BHJs to differentiate phase-separated donor and acceptor domains with nanometer scale resolution.

Departmental Webpage

(a) Topography of SWCNTs on top of P3HT/PCBM in the dark. (b) KFFM image in the dark. (c) KFFM image under illumination. (d) KFFM values of the cross section. (e) Band schematic diagram of type I heterojunction between P3HT/PCBM and SWCNTs.