This thesis describes the development and characterisation of dye sensitised Inorganic:Organic (10) heterojunction photovoltaic (PV) cells of the form Au/MPc/TiO2/InSnO2 or F-SnO2 (where MPc= copper phthalocyanine, chloroaluminium phthalocyanine or lead phthalocyanine). The transparent TiO2 films were prepared by Sol-Gel techniques and characterised optically, structurally and electrically. The effects of and interactions between Sol-Gel process parameters have shown that the parameters undergo significant interaction with particular effects on the TiO2 film thickness and thickness related properties obtained during dip coating. The film refractive index n was in the range 2.73-1.81 and wavelength dependent. The conductivity of the films derived from Au/TiO2/InSnO2 structure was 4.26x10[-6]S/cm. E[0] varied from 3.4-3.35eV where delta=2 indicting an indirect allowed transition in 1 layer thick films to E[0] ~3.2eV where delta=3 indicating indirect forbidden transition as the number of coating layers increased. The spectral response, dark and illuminated J(V) and dark C(V) characteristics of the dye sensitised 10 PV cells have been determined. Spectral response indicates that all of the organic dyes studied can be used to sensitise Sol-Gel derived TiO2 into the visible region Corresponding photovoltaic and junction parameters were derived. Photovoltaic effects were observed in all devices studied, however cell efficiencies were poor, in the range (eta~0.0001-0.046%). The low quantum efficiencies were anticipated to be a consequence of the presence of recombination centres at the TiO2/MPc heterointerfaces and the high observed series resistance due to the low conductivity of the MPc films. The MPc/TiO2 junction formed a rectifying contact. C(V) analysis indicated that the junction was electrically abrupt. The dark J(V) characteristics were divided into three regimes, (i) A reverse bias regime in which the device acts as a p-n heterojunction, (ii) an intermediate forward voltage regime, where the derived values of m > 2 indicating the presence of a high density of interface states (iii) High forward regime. All devices deviate from the standard diode equation as a consequence of space charge effects in the organic layer, the ideality factors m"2. Temperature dependence measurements of PbPc/TiO2 heterojunctions show that the junction currents are a composite of tunnelling and recombination. PV cell parameters were influenced by changes in ambient conditions, the thickness of organic layers and variations in incident intensity. The J[sc] and V[oc] were proportionally and logarithmically dependent on the incident intensity respectively. The high R[s] is believed to be responsible for the poor cell efficiencies reducing FF, J[sc] and eta. A 30 fold increase in eta was observed when the organic film thickness was reduced from 500nm to 100nm. Exposure to atmosphere reduced eta and is likely to be a consequence of O2 trapping centres. The work has demonstrated the feasibility of a low cost solid state 10 heterojunction photovolatic cell. However improvements in efficiency are required to produce a commercially viable device.

Fully conjugated coil-like polymer poly-(3-hexylthiophene) (P3HT) and aromatic heterocyclic copolymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b¡¬]- dithiophene)-alt-4,7-(2,1,3-benzothiadiazole] (PCPDTBT) were applied separately as donors mixed with derivatized carbon fullerence [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) serving as an acceptor. Single layer photovoltaic cells of ITO/ PEDOT:PSS/polymer:PC61BM/LiF/Al were fabricated to study photovoltaic effect of layer thickness, thermal annealing, composition variance, and processing solvent. At a P3HT:PC61BM weight ratio of 1:1, the thermally annealed photovoltaic cells achieved a conversion efficiency (£bp) of 4.58 % from enhanced contact between cathode and active layer. At a PCPDTBT:PC61BM weight ratio of 1:1.25, the best £bp was 2.62 %. The efficiency difference was due to PCPDTBT:PC61BM was highly phase separated preventing the formation of conductive interpenetrating network to facilitate charge transport. Its device fill factor was limited to be 38 %. Under the same spin coating speed, solutions of different PC61BM concentration would yield different spun film thickness leading to large change in conversion efficiency (£bp). At a constant active layer thickness, £bp tended to be stable indicating that £bp was affected more by the layer thickness than by PC61BM concentration. A layer of mixing P3HT: PCPDTBT: PC61BM would expand the absorption range from visible to near infrared. However, an increased PCPDTBT concentration did not help £bp. This is due to charge transport imbalance between P3HT and PCPDTBT leading to an £bp less than those of individual blends with PC61BM. Device £bp was consistently higher for using a solvent with a boiling point higher than polymer glass transition temperature (Tg).

Due to entropy and Van der Waals¡¦ interaction, carbon nanotubes tend to aggregate degrading their excellent opto-electronic properties and limiting their applications. Chemical derivatizations were applied to the multi-wall carbon nanotube (MWCNT) by esterificating with different lengths of aliphatic pendants (COOC4H9, COOC10H21, and COOC18H37) to decrease the MWCNT aspect ratio to facilitate its dispersion, and to observe its percolation behavior. FTIR analysis revealed the more relevant absorption peaks of C-H at 2917 cm-1, 2846 cm-1 and C=O at 1733 cm-1 from the derivatization. H1-NMR showed that the aliphatic pendant functionalized MWCNT from the signals of OCH2 at £_ = 3.64 ppm, CH2 at £_ = 1.25 ppm, and CH3 at £_ = 0.88 ppm. Raman scattering indicated that esterification caused the ID/IG absorption peak area ratio to decrease. In applications, the electric conductivity was measured on thin-films of MWCNT:Poly-(3-hexylthiophene) (P3HT) as a function of nanotube content. Accompanied with nanotube doping concentration increased, the electric conductivity parallel to film surface (£m||) could range from an undoped value 1.4¡Ñ10-6 S/cm up to 1.2¡Ñ10-2 S/cm. The conductivity percolation threshold concentration decreased as the MWCNT aspect ratio increased due to the average distance between the nanotubes becoming sufficiently small for charges to hopping through P3HT. By incorporating [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), bulk heterojunction photovoltaic (PV) cells of ITO/PEDOT:PSS/MWCNT:[PC61BM:P3HT]/LiF/Al were fabricated. By varying the ratio of MWCNT to the PC61BM:P3HT (0.8:1) mixtures, the PV cells showed the maximum power conversion efficiency (£bp) close to 4 % with MWCNT-COOC4H9 at a doping concentration of 0.01 wt. %.

Fully conjugated heterocyclic aromatic rod-like polymer poly-p-phenylene- benzobisoxazole (PBO) and coil-like poly-(3-hexylthiophene) (P3HT) were applied as opto-electronically active layer. The two polymers mixed with nano-carbon particles, having excellent optical absorption and electric conductivity, of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) or esterified multi-wall carbon nano-tube (MWNT-COOC10H21) as well as a hole transporting layer of PEDOT:PSS. Photovoltaic (PV) cells of indium-tin-oxide (ITO)/PEDOT:PSS/nano-carbon particle:fully conjugated polymer/Al were fabricated for optical and electrical characterizations. Tri-layered structure of ITO/PEDOT:PSS/PBO/PCBM/Al produced a straight current-voltage relation showing no PV effects. Upon changing the active layer into PCBM doped P3HT layer (PCBM:P3HT), it produced good PV effects suggesting that the doped layer had a penetrating network to facilitate the PV effects. When PCBM or MWNT-COOC10H21 was doped into P3HT, the device PV effects were increased significantly with nano-carbon particle concentration. The direct-current electric conductivity parallel to the film surface (£m¡ü)was increased with the nano-carbon particle concentration. By changing the thickness of hole transporting PEDOT:PSS and of opto-electronically active layers, it was found that when the PEDOT:PSS layer was decreased from 90 nm to 32 nm, there was a slight increase of PV cell efficiency. The active layer of PCBM:P3HT with a thickness of 99 nm had the best optical absorption and charge transport leading to an increase of PV cell efficiency.

Today, there is an ever-growing demand for compact, and energy autonomous, implantable biomedical sensors. These devices, which continuously collect in vivo physiological data, are imperative in the next generation patient monitoring systems. One of the fundamental challenges in their implementation, besides the obvious size constraints and the tissue-to-electronics biocompatibility impediments, is the efficient means to wirelessly deliver power to them. This work addresses this challenge by demonstrating an energy-autonomous and fully-integrated implantable sensor chip which takes advantage of the existing on-chip photodiodes of a standard CMOS process as photovoltaic (PV) energy-harvesting cells. This 2.5 mm × 2.5 mm chip is capable of harvesting [mu]W’s of power from the ambient light passing through the tissue and performing real-time sensing. This system is also MRI compatible as it includes no magnetic material and requires no RF coil or antennae. In this dissertation, the optical properties of tissue and the capabilities of the CMOS integrated PV cells are studied first. Next, the implementation of an implantable sensor using such PV devices is discussed. The sensor characterizing and the in vitro measurement results using this system, demonstrate the feasibility of monolithically integrated CMOS PV-driven implantable sensors. In addition, they offer an alternative method to create low-cost and mass-deployable energy autonomous ICs in biomedical applications and beyond. / text

>Magister Scientiae - MSc / As the demand for energy is constantly increasing, researchers are looking at various methods of energy production. Following the rise of solar energy becoming a major player, researchers are looking at kesterite materials, Cu2ZnSn(S,Se)4 (CZTS) for photovoltaic applications as they demonstrate many excellent characteristics making them highly suitable for use in thin-film solar cells. Consequently, there are major drawbacks of using kesterite materials for photovoltaic applications such as their point defects and secondary phases. Cerium and iron oxyselenides (Ce2O2Fe2OSe2) are a member of the chalcogenide family and by introducing this chalcogenide into the kesterite structure there would be an improvement in the semiconducting property of the kesterite material. The focus of this research is to dope the kesterite material with nanoscopic cerium and iron oxyselenides in order to reduce the band gap of the kesterite material, thereby improving its light absorption, thus, resulting in a more efficient photovoltaic effect.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20582号 / 工博第4362号 / 新制||工||1678(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 陰山 洋, 教授 安部 武志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The aim of the diploma work is to introduce analytical methods concerning solar panels and systems. Firstly, the attention is drawn to a principle of photovoltaic conversion including an explanation of photoelectric phenomenon as well as the issue of P-N junction considered to be the fundamental building block of a solar cell. With respect to the fact that the diploma work is to be focused on testing of solar panels and the identification of defects in solar cells, the work describes individual solar cells, solar panels as well as individual methods of defect identification. Secondly, the work includes sections dealing with the assessment of the measurement performed by using electroluminescence method as well as the measurement method of volt-ampere parameters. The last section of the work includes the assessment of solar panel aging after one-year performance using the electroluminescence measurement method.

Fabrication of molecular spin devices with ferromagnetic electrodes coupled with a high spin molecule is an important challenge. This doctoral study concentrated on realizing a novel molecular spin device by the bridging of magnetic molecules between two ferromagnetic metal layers of a ferromagnetic-insulator-ferromagnetic tunnel junction on its exposed pattern edges. At the exposed sides, distance between the two metal electrodes is equal to the insulator film thickness; insulator film thickness can be precisely controlled to match the length of a target molecule. Photolithography and thin-film deposition were utilized to produce a series of tunnel junctions based on molecular electrodes of multilayer edge molecular electrodes (MEME) for the first time. In order to make a microscopic tunnel junction with low leakage current to observe the effect of ~10,000 molecules bridged on the exposed edge of a MEME tunnel barrier, growth conditions were optimized; stability of a ~2nm alumina insulator depended on its ability to withstand process-induced mechanical stresses. The conduction mechanism was primarily 1) tunneling from metal electrode to oranometalic core by tunneling through alkane tether that acts as a tunnel barrier 2) rapid electron transfer within the oranometalic Ni-CN-Fe cube and 3) tunneling through alkane tether to the other electrode. Well defined spin-states in the oranometalic Ni-CN-Fe cube would determine electron spin-conduction and possibly provide a mechanism for coupling. MEME with Co/NiFe/AlOx/NiFe configurations exhibited dramatic changes in the transport and magnetic properties after the bridging of oranometalic molecular clusters with S=6 spin state. The molecular cluster produced a strong antiferromagnetic coupling between two ferromagnetic electrodes to the extent, with a lower bound of 20 erg/cm,2 that properties of individual magnetic layers changed significantly at RT. Magnetization, ferromagnetic resonance and magnetic force microscopy studies were performed. Transport studies of this configuration of MEME exhibited molecule-induced current suppression by ~6 orders by blocking both molecular channels and tunneling between metal leads in the planar 25μm2 tunnel junction area. A variety of control experiments were performed to validate the current suppression observation, especially critical due to observed corrosion in electrochemical functionalization step. The spin devices were found to be sensitive to light radiation, temperature and magnetic fields. Along with the study of molecular spin devices, several interesting ideas such as ~9% energy efficient ultrathin TaOx based photocell, simplified version of MEME fabrication, and chemical switching were realized. This doctoral study heralds a novel molecular spin device fabrication scheme; these molecular electrodes allow the reliable study of molecular components in molecular transport.

La texturisation de matériaux par irradiation laser ultracourt est un procédé permettant de modifier les propriétés optiques et électriques de la matière en formant des nano et microstructures en surface, apparaissant au cours des irradiations successives. Le contrôle du procédé et le développement des applications nécessitent une compréhension des mécanismes mis en jeu. Les processus intervenant sont étudiés à l'aide de simulations numériques, et sont comparés à des résultats expérimentaux. L'étude est menée dans le cadre de l'augmentation du rendement des cellules photovoltaïques basées sur du silicium massif. / Ultrashort laser pulsed texturing is a process which allows to modify optical and electrical properties of matter, through formation of nano and micro structures on surface, appearing from pulse to pulse. Control of the process and developments of the potential applications need a good knowledge of the formation mechanisms. Processes occuring during the interaction are studied using numerical simulations and are compared to experimental results. The study aims to increase the efficiency of solar cells based on bulk silicon.