Kang-Shyang Liao

Electrochemically crosslinked surface-grafted PVK polymer brushes as a hole transport layer for organic photovoltaics

Electrochemically crosslinked surface-grafted poly(N-vinylcarbazole) (PVK) brushes as hole transport layers (HTLs) on a photovoltaic device have been demonstrated using SI-RAFT polymerization. Comparable performance to PEDOT:PSS/P3HT:PCBM based devices was achieved. A main advantage is strong adhesion to ITO with a possible long-term stability against acid dopants and oxygen.

Stable organic photovoltaics using Ag thin film anodes

The interaction at the interface between a metal electrode and photoactive polymer is crucial for overall performance and stability of organic photovoltaics (OPVs). In this article, we report a comparative study of the stability of thin film Ag and indium tin oxide (ITO) as electrodes when used in conjunction with an interfacial PEDOT:PSS layer for P3HT:PCBM blend OPV devices. XPS measurements were taken for Ag and ITO/PEDOT:PSS layered samples with different exposure times to ambient conditions (∼25 °C, ∼50% relative humidity) to investigate the migration of Ag and In into the PEDOT:PSS layer. The change in efficiency of OPVs with a longer exposure time and degree of migration is explained by the analysis of XPS results. We propose the mechanism behind the interactions occurring at the interfaces. The efficiency of the ITO electrode OPVs continuously decreased to below 10% of the initial efficiency. However, the Ag devices displayed a slower degradation and maintained 50% of the initial efficiency for the same period of time.

Formation of highly conductive composite coatings and their applications to broadband antennas and mechanical transducers

Tight networks of interwoven carbon nanotube bundles are formed in our highly conductive composite. The composite possesses propertiessuggesting a two-dimensional percolative network rather than other reported dispersions displaying three-dimensional networks. Binding nanotubes into large but tight bundles dramatically alters the morphology and electronic transport dynamics of the composite. This enables itto carry higher levels of charge in the macroscale leading to conductivities as high as 1600 S/cm. We now discuss in further detail, the electronic and physical properties of the nanotube composites through Raman spectroscopy and transmission electron microscopy analysis. When controlled and usedappropriately, the interesting properties of these composites reveal their potential for practical device applications. For instance, we used this composite to fabricate coatings, whic improve the properties of an electromagnetic antenna/amplifier transducer. The resulting transducer possesses a broadband range up to GHz frequencies. A strain gauge transducer was also fabricated using changes in conductivity to monitor structural deformations in the composite coatings.

Fabrication, characterization, and optical modeling of a new architecture for organic photovoltaics: The vertically orientated stack device

We introduce a new architecture for organic photovoltaics based on vertically orientated devices. The fabrication, device characteristics, and an optical model of the stack organic photovoltaic (OPV) device are presented. This new architecture gives rise to an alternative to the common flat-panel structure, which was originally conceived for the first silicon devices. The OPV stack device has an increased short circuit current density, fill factor, and power-conversion efficiency, as opposed to the standard flat-panel device.

Investigation of recombination dynamics for indium tin oxide-free organic photovoltaics by illumination dependence study

Highly conductive poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used as an anode material to construct flexible organic photovoltaics on plastic, poly(ethylene naphthalate) (PEN) substrates with a device structure of PEN/modified PEDOT:PSS/poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Al. The indium tin oxide (ITO)-free flexible device exhibits a 20% increase in power conversion efficiency under 1 sun with a higher open circuit voltage (0.67 V) compared to that of the reference device having an ITO anode on a glass substrate (0.54 V). A study of the different recombination mechanisms within these two device structures is carried out by comparing the illumination responses of open circuit voltage as well as short circuit current. The results explain the varying trend of fill factor and power conversion efficiency with respect to the light intensity and suggest that a bimolecular recombination mechanism is dominant in the ITO-free devices.