Organic-inorganic nanocomposites for photovoltaic and other optoelectronic applications

Novel nanocomposite organic-inorganic compounds have been synthesised with several layered inorganic hosts (V2O5, MoO3 and ZnPS3). Three synthetic methods were used; direct intercalation taking advantage of any redox chemistry between the host and guest, an ion-exchange route in which pre-intercalated alkali metal cations were exchanged for organic guest cations and recrystallization of the dissolved host around the organic guest species. All methods afforded the intercalation of conducting polymers into the interlayer space of the inorganic hosts. Full characterisation of the composites was carried out as well as the determination of their (opto)electronic properties. The direct method was used to intercalate polyaniline (AnAn+) and 3,4-ethylenedioxythiophene (EDOT) into V2O5 2-amino-5-phenylpyridine (2A5PhPyr) used an acid-base direct intercalation method. AnAn+ and 2A5PhPyr exhibited bilayer structures with AnAn+ parallel to the inorganic layers. EDOT, however, produced a monolayer intercalate and all three products exhibited similar room temperature conductivities (~10-2 – 10-3 Sm-1 ). 2A5PhPyr and 5-aminoquinoline (5AQ) were intercalated into V2O5 and MoO3 using the ion-exchange method. A copolymer of 1,4-phenylenediamine and hydroquinone (1,4PDA-HQ) was also intercalated into V2O5 and 1,2-phenylenediamine (PDA) was intercalated into V2O5, MoO3 and ZnPS3 by this method. 2-Aminothiazole (2AmThia) was intercalated into MoO3 using ion-exchange. PDA and 5AQ exhibited bilayer conformation upon intercalation while PDA was a monolayer intercalant in ZnPS3. PDA intercalated V2O5 and MoO3 exhibited the highest conductivities (~10-1 Sm-1 ) whereas 2AmThia intercalated MoO3 exhibited the lowest conductivity (~10-4 Sm-1 ). Aniline (An) was intercalated into MoO3 via a novel recrystallization method resulting in room temperature conductivity similar to that of the 2AmThia intercalated MoO3 (~10-4 Sm-1 ). The novel ion-exchange of ZnPS3 with Mg2+ yielded MgxZnyPS3 which exhibited substantial interlayer expansion suspected to be due to hydration of intercalated Mg2+. The Mg2+ cations were present in the interlayer spacing and did not occupy the vacant Zn2+ sites. The intercalated materials exhibited p-type properties, unlike their n-type hosts. Using aluminium, copper, tin, zinc and FePS3 as blocking contacts, Schottky devices of the composite materials exhibited improved semiconductor properties over their host materials. Prototype photosensitive devices using V2O5/AnAn+ , V2O5/EDOT, V2O5/2A5PhPyr, MoO3/PDA and ZnPS3/PDA were constructed by spin coating the active material onto ntype silicon and p-type FePS3 and are reported for the first time. The devices exhibited increased photocurrents under ambient light or an incandescent lamp illumination. Maximum efficiencies were 0.71% and 0.26% under ambient light and incandescent lamp respectively. The devices exhibited low charge mobilities of ~8 x 10-10 m 2V -1 s -1 and ~3 x 10-11 m 2V -1 s -1 under ambient sunlight and incandescent light respectively. It was noted that the polymer guests in their most conductive forms produced the best semiconducting and photoactive devices. Overall, this work provided a proof-of-concept that the low-cost organic-inorganic nanocomposite materials synthesised exhibited promising novel optoelectronic properties when incorporated into junction devices

Inkjet printing of resistive-type humidity sensor for harsh environments

A flexible resistive-type humidity sensor for harsh environments is successfully designed and fabricated by an inkjet printing method using a Dimatix materials printer (DMP-2800 series from Fujifilm). Construction of the sensors is based on inkjet printed interdigitated silver electrodes on a polyimide flexible substrate along with an inkjet printable polyaniline (PANi) as humidity sensitive material. A copolymer of ethylene and vinyl alcohol (EVOH) is used as sensor protective coating. Double strand water- soluble PANi ink is synthesized by polymerization of aniline monomers with poly(4- styrenesulfonic acid) (PSSA) as a template. Manufactured devices showed high sensitivity (/% @ 45%RH) to humidity with good linearity (R-squared correlation value of 0.99) and fast absorption and desorption responses over a broad range of humidity (/5-95%RH). The response time for the sensors without EVOH coating on top is around 5 and /5 seconds for absorption and desorption, respectively. The response time for the coated sensors is about 40 and //0 seconds for absorption and desorption, respectively. Sensors showed small hysteresis (about 3%) while a protective polymer coating provided a barrier to damage or false signals due to solvents and chemicals. Fabricated sensors are characterized in order to investigate the structure and morphology of the thin films. UV-Visible spectroscopy is used to obtain information on PANi in solution form and to confirm that PANi in the form of emeraldine salt is obtained. FT-IR spectroscopy is used to verify the incorporation of the PSSA into PANi. SEM microscopy method is used to characterize the PANi-PSSA in powder form and the AFM method is used to show the morphology of the thin films

Gas sensing using an organic/silicon hybrid field-effect transistor

This thesis describes the fabrication and properties of novel organic/silicon hybrid field-effect transistor gas sensors. Whilst most of the work used the emeraldine base form of the conductive polymer polyaniline, the response of a device incorporating a metal-free phthalocyanine is also reported. Arrays of p-type transistors in which the gate electrodes were replaced by 'charge-flow' capacitors were fabricated using standard semiconductor processing techniques. Each array consisted of four devices in which the width of metallisation removed from the gate electrode (total width 72 µm) varied from 0 µm (i.e. the control device) to 35 µm. Thin films of the gas-sensitive organic materials were deposited by spin-coating, and chemically patterned within the holes in the gate metallisation. A delay, referred to as the 'turn-on' response, was observed in the drain current on application of a gate voltage. This was shown to depend on the temperature, level of humidity and the presence of certain gases. The electrical operating characteristics of the hybrid device with and without the polyaniline were examined. These included capacitance-voltage measurements, the 'turn-on' response at different temperatures and the variation of threshold voltage with temperature. From these results an understanding of the effect of integrating polyaniline within a p-channel transistor structure was obtained. The 35 µm gate-hole sensor incorporating polyaniline was found to be sensitive to NO(_x) and SO(_2) at room temperature at concentrations as low as 1 or 2 ppm. Decreasing the gate-hole area, and therefore the surface area of polyaniline, reduced the sensitivity of the device. The reactions were found to be reversible, although complete recovery required approximately eight hours. A similar sensor incorporating a metal-free phthalocyanine compound was reversibly sensitive to 2 ppm NO(_x) with a more rapid recovery of five hours. There was no observable response to SO(_2) or H(_2)S up to 30 ppm

Request for Graduate Travel Support to Attend the Nanoelectronic Devices for Defense $ Security (NANO-DDS) Conference 2009. To be Held Sept 28-Oct. 2, 2009 in Ft. Lauderdale FL

The objective of this proposal is to support graduate student attendance to the Nanoelectronic Devices for Defense & Security (NANO-DDS) will be held at the Bahia Mar Beach Resort in Fort Lauderdale, FL during the weeks of September 28 to October 2, 2009. The approach is to recruit students in the science and engineering areas related to nanoelectronic devices research and development with the aim that their attendance will broaden the impact of the meeting to the education experiences and education of future scientists and engineers. There will be a formal reporting procedure that includes a narrative that explains their estimation of the benefit in attending the conference that all student attendees will be required to complete. Intellectual Merit: The conference has been organized as a formal bi-annual meeting for the purpose of reviewing research and development (R&D) activities in the arena of nanoelectronic devices that have direct relevance to critical capability needs for national Defense & Security in the future. The charter of this special conference is to unify and focus the very broad array of nanoelectronic and supporting nanotechnology activities that are currently engaged in reaching the long expected applications payoffs in core defense and security related areas such as sensing, data processing, computation and communications. Broader Impacts: The scientific and technological information and the resulting nanoscale devices and systems Roadmap will be widely disseminated throughout academia/universities, government and industrial institutions and the public at-large (including the entire international community). The conference has made diligent effort to recruit student attendees from underrepresented groups from the nanoscience, nanomaterials, nanofabrication and nanoengineering communities

Solar Cells

The second book of the four-volume edition of "Solar cells" is devoted to dye-sensitized solar cells (DSSCs), which are considered to be extremely promising because they are made of low-cost materials with simple inexpensive manufacturing procedures and can be engineered into flexible sheets. DSSCs are emerged as a truly new class of energy conversion devices, which are representatives of the third generation solar technology. Mechanism of conversion of solar energy into electricity in these devices is quite peculiar. The achieved energy conversion efficiency in DSSCs is low, however, it has improved quickly in the last years. It is believed that DSSCs are still at the start of their development stage and will take a worthy place in the large-scale production for the future

Fabrication and Characterization of Hybrid Metal-Oxide/Polymer Light-Emitting Diodes

Hybrid metal-oxide/polymer light-emitting diodes (HyLEDs) are a novel class of electronic devices based on a combination of electroluminescent organic and charge-injecting metal-oxide components. These devices employ air-stable electrodes, such as ITO and Au, and are therefore well suited for fabrication of encapsulation-free light-emitting devices. The current work is intended to provide an insight into operating mechanisms and limitations of the HyLEDs, and, on the basis of this knowledge, aims at modifying the device architecture in order to improve the performance. The choice of optically transparent metal-oxide charge-injection layers appears to be critical in this respect in order to optimize the electron-hole balance within the polymer layer. Starting from the original device architecture, ITO/TiO2/F8BT/MoO3/Au, which uses ITO as a cathode and Au as an anode, we follow different approaches, such as the use of dipolar self-assembled monolayers and nanoscale structuring of the electron-injecting interface, pursuing the goal of enhancing electron injection into the emissive layer. However, substitution of the electron-injecting layer of TiO2 with ZrO2 is demonstrated to be the most efficient of the approaches employed herein. Further, optimization of the device utilizing the latter metal oxide is demonstrated in terms of deposition and post-deposition treatment of the electron-injecting and electroluminescent layers. Substrate temperature during spray pyrolysis deposition of the electron-injecting layer is found to have a strong influence on the HyLED performance, as well as the precursor solution spraying rate and the layer thickness. On the other hand, post-deposition annealing of the polymer layer is shown to improve the device efficiency and brightness significantly, possible explanations lying in enhancement in polymer luminescence efficiency and formation of a more intimate contact between the electron-injecting and the active polymer layers. Combining electron-transporting (TiO2 and ZnO) and hole-blocking (Al2O3 and ZrO2) materials into a single electron-injecting layer is demonstrated to be an effective strategy of enhancing efficiency in the HyLEDs. The search for a hole-injecting electrode alternative to the conventionally used MoO3/Au leads to the device employing the PEDOT:PSS/VPP-PEDOT system, which though resulting in a poorer device efficiency, provides route for fabrication of vacuum deposition-free organic light-emitting devices. Finally, the HyLED architecture is demonstrated to offer better stability than the conventional architecture using LiF/Al as a cathode. It is hoped that the current work provides a better understanding of the requirements for fabrication of encapsulation-free organic light-emitting devices