We report the synthesis of ZnO aggregates in the presence of lithium salt and the enhancement on the energy conversion efficiency of dye sensitized solar cells when the photoelectrode films consist of as-synthesized ZnO aggregates. The conversion efficiency for ZnO film consisting of aggregates synthesized with lithium involvement is significantly improved up to 5.8%, which is 32% higher than that of 4.4% obtained for pure ZnO film. Such an enhancement can be attributed to the effect of lithium-induced changes on the morphology and crystallinity of aggregates, the optical absorption of films, and the surface chemistry of ZnO, which provides the film with decreased electron trapping and increased refractive index, and enhances the electronic coupling between the dye molecules and ZnO.

One-way to improve organic solar cell efficiency is blending conjugated polymer with a second nanocomposite. We report on blending of freestanding boron- and phosphorous-doped environmental friendly silicon nanocrystals (Si-ncs) with two conjugated polymers i.e. (poly(3-hexylthiophene) (P3HT) and poly[methoxy-ethylexyloxy-phenylenevinilene] (MEH PPV)). The electrochemical etching and pulverization of doped porous silicon films are used for fabrication of photesensitive Si-ncs/polymers blends. Processing of Si-ncs dispersed in polymers allows simple tuning of the Si-ncs concentrations in the blends. The blends with high Si-ncs concentrations are prepared and opto-electric properties are compared and discussed. Both types of polymers containing doped Si-ncs showed a photoconductivity response under illumination AM1.5 at ambient temperature and atmosphere.

Highly conductive (> 103 Ω-1cm-1) and transparent (∼ 90%) In4Sn3O12 films have been deposited using pulsed laser deposition (PLD) on glass substrates held at a temperature of 500°C under varying pressures of oxygen (2.5 mTorr ≤ PO2 ≤ 15 mTorr). The crystallinity and the roughness of the films were found to increase with the pressure of oxygen used during deposition. Electron concentrations of the order of 5×1020 cm-3 and mobilities as high as 30 cm2V-1s-1 were derived from the measurement of Hall coefficients. Both the electronic transport and optical properties of the films were found to be strongly sensitive to the pressure of oxygen used during deposition.

We report dye-sensitized solar cells using low cost carbon nanoparticles as an alternative to platinum as a counter-electrode catalyst for triiodide reduction. The counter carbon-electrode was deposited onto fluorine-doped tin oxide (FTO) by spin coating from an aqueous colloidal suspension of the blend of carbon nanoparticles and TiO2 nanocrystals. DSSC devices were fabricated using a stable Ru complex dye (Z-907) as the sensitizer. The cells based on carbon-nanoparticle counter electrode were made and then compared with those cells from platinum counter electrode at similar fabrication conditions. The results have shown that the device performance in terms of short circuit current density (Jsc), open circuit voltage (Voc) and energy conversion efficiency (η) from the cells based on carbon nanoparticle counter electrode were comparable to those from platinum counter-electrode devices. The carbon nanoparticle based cells have achieved an overall energy conversion efficiency of 5.55% under one sun AM 1.5 illumination (100 mW/cm2). The carbon nanoparticles showed significant potential as a low cost alternative to the current widely-used platinum.

Promising nanostructured device concepts with staggering theoretical efficiencies where quantum confined states are embedded in the intrinsic region of conventional p-i-n solar cells have been proposed. However, practical realizations remain inefficient as these devices suffer from an inherent difficulty in the extraction of photo-generated carriers from the confined states. Within the framework of a “single particle in the box” theory, such shortcomings could be addressed by the use of resonant quantum tunneling designs that can expedite carrier escape. Nonetheless, in material systems studied thus far, the implementation of such design becomes elusive as band offsets between the nanostructure and the host material are distributed between the conduction and valence band leading to the confinement of both holes and electrons (i.e. two particle problem). Our studies of such p-i-n Multi-Quantum Well (MQW) solar cells, only differing by their MQW region composition and geometry, have shown a strong dependence of device performance on quantum wells composition and thickness. Leveraging on the special property of dilute nitrides and using a carefully chosen material system and device design we show the possibility of circumventing this problem by separating the optimization of the valence and conduction band and reducing the issue to a single particle problem. Band structure calculations including strain effects, band anti-crossing models and transfer matrix methods are used to theoretically demonstrate optimum conditions for enhanced vertical transport. High electron tunneling escape probability, together with a free movement of quasi-3 D holes, is predicted to result in enhanced PV device performance. Furthermore, the increase in electron effective mass due to the incorporation of N translates in enhanced absorptive properties, ideal for PV application.

In the study, semiconductor quantum dots (QDs) of CdSe nanocrystals have been demonstrated effective as the light energy harvesting assemblies in solar cells. Colloidal CdSe QDs were synthesized by the one-pot approach and linked through a surface modifier onto titania (TiO2) nanoparticles. The TiO2-CdSe composite, while employed as the photoanode in a photoelectrochemical apparatus, exhibited a higher photon-to-electron conversion efficiency (3-fold) than the TiO2 alone, and also a higher stability for photocurrent generation, according to photocurrent transient responses. The optical absorbance and photoluminescence of the CdSe colloid showed a blue shift in the absorption edge with decreasing the particle size (band energy gap shifts from 2.0 to 2.19 eV), suggesting a quantum size effect. The CdSe particle size was determined up to 5 nm by a transmission electron microscopy. A scheme describing the charge carrier rectification for the coupled semiconductor system is proposed.

Advanced, direct thermal energy conversion technologies are receiving increased research attention in order to recover waste thermal energy in advanced vehicles and industrial processes. Advanced thermoelectric (TE) systems necessarily require integrated system-level analyses to establish accurate optimum system designs. Past system-level design and analysis has relied on well-defined deterministic input parameters even though many critically important environmental and system design parameters in the above mentioned applications are often randomly variable, sometimes according to complex relationships, rather than discrete, well-known deterministic variables. This work describes new research and development creating techniques and capabilities for probabilistic design and analysis of advanced TE power generation systems to quantify the effects of randomly uncertain design inputs in determining more robust optimum TE system designs and expected outputs. Selected case studies involving stochastic TE .material properties demonstrate key stochastic material impacts on power, optimum TE area, specific power, and power flux in the TE design optimization process. Magnitudes and directions of these design modifications are quantified for selected TE system design analysis cases.

Thermoelectric materials are being important due to their application in both thermoelectric power generation and microelectronic cooling. The thermoelectric power generations convert the heat change to electricity. The waste of heat could be useful if the thermoelectric power generation is applied. Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. A high thermal conductivity causes too much heat leakage through heat conduction. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. In this study, we prepared thermoelectric generator devices of SiGe at the thickness of 112 nm using the ion beam assisted deposition (IBAD) system. Rutherford Backscattering Spectrometry (RBS) analysis was used for the elemental analysis. The 5 MeV Si ion bombardment was performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the film to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardment we measured the cross plane Seebeck coefficient, electrical conductivity by Van der Pauw method, and thermal conductivity by 3w method for different fluences.

The electronic properties of an InN/anatse bilayer, proposed as a replacement for the dye/semi-conductor interface in Dye Sensitized Solar Cell[1, 2], are measured. RF sputtered thin films of anatase and InN are used as the “dye” replacement. . Two types of InN film are prepared: polycrystalline samples deposited at high temperature, with an optical band gap of < 1 eV, and as-deposited (at least partially amorphous) samples with an optical band gap >1 eV. Energy Dispersive X-ray fluorescence, X-ray Diffraction, and Raman spectroscopy are used to characterize the samples. The resistance in the dark and under illumination are measured. The samples deposited at high temperature are crystalline and have a sheet resistivity ≈ 4 Ω/⁐, and display no photoconductivity. The partially amorphous samples have sheet resistivity of ≈ 500Ω/⁐. Since both types of InN films, including high quality (based on band gap) polycrystalline InN, do not show increased conductivity with light, we conclude that a solar cell based on an InN/anatase bilayer is not feasible.

Single and multi junction hybrid devices comprising oligoacenes, PbS quantum dots (PbS-QD) and C60 are demonstrated. A greatly improved performance of the PbS-QD /C60 system was obtained in this work. Furthermore, a study of using acenes (pentacene, tetracene) as light absorbers and photoinduced electron donors to PbS-QD was carried out. Fabricated devices were characterized under 1 Sun simulated solar irradiation and external quantum efficiency (EQE) measurements. The initial hybrid devices demonstrated up to 0.14 % power conversion efficiency under AM1.5G illumination and up to 16 % EQE at 400 nm. The single junction (PbS-QD/C60) devices demonstrated greater than 1.2 % EQE at 1100 nm while multi junctional tetracene/PbS-QD/C60 devices exhibited up to 0.2 % EQE in the infrared region (1100 nm). Ultraviolet photoelectron spectroscopy was used to measure the molecular energy levels in the system under discussion to justify the photoinduced charge transfer. This work demonstrates new device systems which can be potentially be utilized to fabricate high efficient broad band absorbing hybrid photovoltaics.

We have developed a new thermoelectric power-generating module composed of 72 pieces of n-type Ba8Al18Si28 clathrate elements made by arc melting. The Seebeck coefficient, specific electric resistance and thermal conductivity of Ba8Al18Si28 clathrate were 250 μV/K, 1.9 mΩcm and 3.1 W/mK at 500 °C, respectively, and the thermoelectric figure of merit (ZT) was 0.8. The new thermoelectric module was constructed using only n-type thermoelectric elements connected in series with hook-shaped electrodes. The open-circuit voltage of the module increased with hot-side temperature up to 1.8 V at 500 °C and generated 0.24 W. The module was successfully used to charge lithium-ion batteries for mobile phones.

We have deposited 50 nano-layers of 710 nm of SiO2/SiO2+ZrNiSn with a periodic structure consisting of alternating layers where each layer is about 14 nm thick. The purpose of this research is to generate nanolayers of nanostructures of ZrNiSn with SiO2 as host and as buffer layer using a combination of co-deposition and MeV ion bombardment taking advantage of the energy deposited in the MeV ions track to nucleate nanostructures. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/ĸ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and ĸ is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing ĸ. The electrical and thermal properties of the layered structures were studied before and after bombardment by 5 MeV Si ions at seven different fluences ranging from 1014 to 1015 ions/cm2 in order to form nanostructures in layers of SiO2 containing few percent of ZrNiSn. Rutherford Backscattering Spectrometry (RBS) was used to monitor elemental analysis of the film.