A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together
with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical
sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing,
on a chip area of 0.25mm2. Direct charging of the target battery (e.g., NiMH microbattery) is achieved with end-to-end
efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the
voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells
show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, Voc, of 450-500mV. To match the
battery’s voltage the miniaturised solar cells (~1mm2 area) are connected in series via wire bonding. The chemical sensor
platform (mm2 area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature
range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both
temperature and H2 concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are
less than 350nW and 2.1 μW respectively. Low-power miniaturised chemical sensors of liquid analytes through
microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further
miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire
We report efficient organic bulk heterojunction solar cells, utilizing spray-patterned films of single-wall carbon nanotubes for the transparent electrode. High power conversion efficiencies of up to 3.6% were obtained using a blend of poly(3-hexylthiophene) and phenyl-C61 butyric acid methyl ester as the active layer, comparable to conventional devices utilizing indium tin oxide as the transparent electrode.
We studied hole injection from the conducting polymer blend poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) by optical spectroscopy and characterization of organic light-emitting diodes (OLEDs). Electroabsorption (EA) spectroscopy was used to measure the built-in potential of polyfluorene-based OLEDs with indium tin oxide (ITO) or poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) anodes. Although the work function of PEDOT:PSS is 5.1 eV, the inferred anode work function matches the ionization potential of the emitting polymer. We conclude that the Fermi level at the PEDOT:PSS/polyfluorene interface is pinned to the highest-occupied molecular orbital (HOMO) of the emitting polymer, permitting efficient hole injection. To test this hypothesis, we fabricated OLEDs using the archetypical molecular semiconductor, tris(8-hydroxyquinoline) aluminum (III) (Alq3). Although the anticipated hole injection barrier is 0.7 eV, OLEDs with Alq3 deposited onto PEDOT:PSS operate at a lower bias and higher power efficiency than OLEDs with a hole transport layer. The quantum efficiency of single layer Alq3 and rubrene-doped Alq3 devices is equal to that of multi-layer devices, showing that EL is not quenched by PEDOT:PSS.
We report that polymer light emitting diodes (pLEDs) and polymer photodetectors can be integrated on disposable polydimethylsiloxane [PDMS] microfluidic flowcells to form hybrid microchips for bioluminescence applications. PLEDs were successfully employed as excitation light sources for microchip based fluorescence detection of microalbuminuria (MAU), an increased urinary albumin excretion indicative of renal disease. To circumvent the use of optical filters, fluorescence was detected perpendicular to the biolabel flow direction using a CCD spectrophotometer. Prior to investigating the suitability of polymer photodiodes as integrated detectors for fluorescence detection, their sensitivity was tested with on-chip chemiluminescence. The polymer photodetector was integrated with a PDMS microfluidic flowcell to monitor peroxyoxalate based chemiluminescence (CL) reactions on the chip. This work demonstrates that our polymer photodetectors exhibit sensitivities comparable to inorganic photodiodes. Here we prove the concept that thin film solution-processed polymer light sources and photodetectors can be integrated with PDMS microfluidic channel structures to form a hybrid microchip enabling the development of disposable low-cost diagnostic devices for point-of-care analysis.
The properties of electrically pumped organic laser devices are investigated by the self consistent numerical solution of the spatially inhomogeneous laser rate equations coupled to a drift-diffusion model for the electrons, holes and singlet excitons. By fully taking into account the effect of stimulated emission on the exciton population, we determine the spatial and temporal evolution of the photon density in organic multilayer structures. We apply the model to calculate laser threshold current densities and investigate transient phenomena like the delay of radiation onset. By performing systematic parameter variations, we derive design rules for potential organic laser diode structures.
We report a low cost device for performing chemiluminescent (CL) assays in a miniaturised format. The device comprises a poly(dimethylesiloxane) microfluidic chip for performing the CL assay coupled to a polymer photodiode based on a 1:1 blend by weight of poly(3-hexylthiophene) [P3HT] and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 [PCBM]. The integration of organic photodiodes with microfluidic chips offers a promising route to low cost fully integrated diagnostic devices for point-of-care applications.
Electromodulation (EM) spectroscopy has been used to probe the electric field distribution in polymer light-emitting diodes. Below the turn-on bias, the EM spectrum is dominated by electroabsorption of the emissive layer. The electroabsorption signal vanishes at the turn-on bias. Under operation, the EM spectrum is due to by excited state absorption from injected charge and bleaching of the ground state absorption of the emissive layer. We conclude that the internal electric field is effectively screened by accumulation of trapped electrons at the anode.
We use electromodulation (EM) spectroscopy to probe the electric field distribution in polymer light-emitting diodes. The EM spectrum below the turn-on bias is dominated by electroabsorption of the emissive layer but vanishes completely above the turn-on bias. The EM spectrum above turn-on is due entirely to absorption and bleaching effects arising from injected charge. The total elimination of the electroabsorption signal indicates that the internal electric field is effectively screened by the injected charge, and this effect is attributed to accumulation of trapped electrons close to the anode.
Electromodulation (EM) spectroscopy has been used to probe the electric field distribution in polymer light-emitting diodes. Below the turn-on bias, the EM spectrum is dominated by electroabsorption of the emissive layer. The electroabsorption signal vanishes at the turn-on bias. Under operation, the EM spectrum is due to excited state absorption from injected charge and bleaching of the ground state absorption of the emissive layer. We conclude that the internal electric field is effectively screened by accumulation of electrons at the anode.
The synthesis and luminescent properties of the homopolymers (4,5) and copolymers (9,10) carrying ion-transporting side chains are reported. When fabricated as alight emitting electrochemical cell the copolymer 10 exhibited a significant reduction in turn-on voltage and improved luminous efficiency compared with a conventionally fabricated polymer light emitting device. Similar results were observed with the pyridine copolymer 13. The model meta-linked trifluoromethyl substituted distyrylbenzene derivative 16 has been synthesized and its crystal structure has been determined with a view to evaluating the related polymers as charge transporting materials.