John Tumbleston, UNC
Photonic Crystal Organic Solar Cells
Incorporating photonic crystal (PC) geometries into the design of organic solar cells has resulted in both electrical and optical improvements in device performance. A PC structure can be readily fabricated over large areas using the Pattern Replication In Nonwetting Templates (P.R.I.N.T.) technique even with the demand of nanoscale material periodicity. Device performance will be discussed where the PC cells successfully target desired regions of the solar spectrum for averaged 3-fold absorption enhancements in part through multiple excitation resonances. We also show efficiency improvements of ~70% that result not only from greater absorption, but also from electrical enhancements.
Qing Peng, NC State
Surface Functionalization by Atomic Layer Deposition
Chemical modification of substrates with functional reactive molecular layers, especially the amino (-NH2) terminated layers, attract a lot of interests due to the wide range of applications in electronics, biology, catalyst, energy etc. Currently one of the major methods is to chemically assemble amino terminated silanes onto substrates, which are bearing -OH groups, for example metal oxides. As a well-known method, atomic layer deposition has been widely used to deposit highly conformal and uniform metal oxide films (Al2O3, ZnO, Fe2O3, SiO2, TiO2 etc) onto different substrates, including complex 3 dimensional nanostructures and inert surfaces at relative low temperatures. In this study, sequential low temperature atomic layer deposition of metal oxides and amino silane self-assembly monolayer (SAM), is demonstrated as a new method to modify inert surface with amino group. Specifically, the deposition behavior of ALD of aminosilane (specifically γ-aminopropyl triethoxysilane: APTES) with H2O on the in-situ generated Al2O3 ALD film is monitored by in-situ quartz crystal microbalance (QCM) at different deposition temperatures (120 and 150 ˚C). The in-situ QCM data shows that on Al-OH surface, the APTES&H2O ALD chemical adsorption is saturated after ~ 10 cycles. However, the 1st cycle of mass uptake of APTES counts about 80% of the total mass uptake of APTES SAM ALD at 120 ˚C and 60% at 150 ˚C. The ex-situ X-ray photoelectron spectroscopy measurement confirmed the N components on the surface, which is about 2 atomic percentages at reaction temperature of 120 ˚C. Moreover, in-situ QCM measurement also confirmed that APTES could react with Al-CH3 terminated Al2O3 ALD film surface. More detail analysis from in-situ Fourier transform infrared spectroscopy will be presented as well to illustrate the detail surface reaction chemistry. Moreover the APTES&H2O ALD cycles are also studied on ZnO ALD film by QCM and other techniques. Furthermore the application of this technique on modification of the inert three dimensional fiber system will be discussed.
Meredith J. Hampton, UNC
A PRINT approach to hybrid organic-inorganic PV devices
With global energy demands increasing yearly and current energy production dependent on a finite supply of fossil fuels, solar energy provides a sustainable energy alternative to traditional energy sources. Recent advances in solar energy research have shown organic-based photovoltaic cells, when configured into bulk heterojunction (BHJ) morphologies, exhibit high collection efficiencies if the morphology of phase separation is controlled to the extent that any point in the network is within the exciton diffusion length of a donor/acceptor junction and the network is bicontinuous. In this research effort, we use a PFPE stamp to control the morphology of the donor-acceptor interface within devices. The low-surface energy, chemically resistant, variable modulus, fluoropolymer based molds used in PRINT provide a route to patterning, with nanometer resolution, ?hard? inorganic oxide structures typically used as acceptor materials in hybrid organic solar cells such as TiO2 and CdSe. This ?top-down? approach allows for patterning over large areas and for the functionalization of the donor/acceptor interface.
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