The sun provides us with a surplus of energy convertible to electricity using solar cells. This thesis focuses on solar cells based on chalcopyrite (CIGSe) as well as kesterite (CZTS(e)) absorber layers. These materials yield record efficiencies of 20.4 % and 11.1 %, respectively. Especially for CZTS(e), the absorber layers often do not consist of one single desired phase but can exhibit areas with deviating material properties, referred to as secondary phases. Furthermore, several material layers are required for a working solar cell, each exhibiting interfaces. Even though secondary phases and interfaces represent a very small fraction of the solar cell they can have a profound influence on the over-all electrical solar cell characteristics. As such, it is crucial to understand how secondary phases and interfaces influence the local electrical characteristics. Characterising secondary phases and interfaces is challenging due to their small sample volume and relatively small differences in composition amongst others. This is where electronmicroscopy, especially transmission electron microscopy, offers valuable insight to material properties on the microscopic scale. The main challenge is, however, to link these material properties to the corresponding electrical characteristics of a solar cell. This thesis uses electron beam induced current imaging and introduces a new method for JV characterisation of solar cells on the micron scale. Combining microscopic structural and electrical characterisation techniques allowed identifying and characterising local defects found in the absorber layer of CIGS solar cells after thermal treatment. Furthermore, CZTSe solar cells in this thesis exhibited a low photo-current density which is traced to the formation of a current blocking ZnSe secondary phase at the front contact interface. The electron microscopy work has contributed to an understanding of the chemical stability of CZTS and has shown the need for an optimised back contact interface in order to avoid chemical decomposition reactions and formation of detrimental secondary phases. With this additional knowledge, a comprehensive picture of the material properties from the macroscopic down to the microscopic level can be attained throughout all required material layers.

För att undersöka skillnad i prestationsförmåga mellan celler sensiterade med växtextraktsbaserad färg, och celler sensiterademed ruteniumkomplex-baserad färg, samt huruvida presskraften påverkar en cells prestationsförmåga, tillverkades icke-slutna fotoelektrokemiska färg-sensiterade solceller med tunnfilmsfotoelektroder av pressad, nanoporös titandioxid. Cellerna pressades med tre olika presskrafter och sensiterades med växtextraktsfärg från rödkål, rödbeta, viol och henna, samt en ruteniumkomplex-baserad färg som fick utgöra kontrollbetingelse. För varje cell uppmättes IPCE- och iV-värde och motsvarande fyllnadsgrad (fill factor) och dessa jämfördes. Ingen signifikant skillnad kunde fastställas mellan celler pressade med olika presstryck. Bland cellerna sensiterade med växtextraktbaserad färg presterade rödbeta bäst. Cellen med högst effektivitet hade fyllnadsgraden 70%. Emellertid uppvisade de växtfärgade cellerna genomgående sämre effektivitet än de rutenium-sensiterade och fotoströmmarna var mycket låga. IPCE-värdena var allmännt låga: den bäst presterande cellen hade ett IPCE-värde på något över 0,06 i våglängdsintervallet 440-470 nm. En förklaring till detta är de övriga ämnen som förutom pigment återfinns i de växtbaserade färgerna. Dessa hindrar pigmentmättnad och förhindrar att växtfärgen når ruteniumfärgens intensitet. En annan anledning består i svårigheten att passa ihop energinivåerna i cellens elektrolyt-halvledarsystem med energinivåerna hos pigmentet i växtfärgen. / Non-sealed photoelectrochemical dye sensitised solar cells (DSSC) with pressed nanoporous TiO2 thin film photoelectrodes were manufactured for the purposes of finding out whether plant extractbased dye sensitised cells can perform as well as ruthenium complex-based dye sensitised cells and whether the pressing force affects the cell performance. The cells were pressed with three different pressing forces and sensitised with plant extracts from red cabbage, beetroot, violet and henna, as well as with a ruthenium complex-based dye for comparison. The IPCE and iV values and the corresponding fill factors of the cells were evaluated and compared. No significant difference between the cells pressed with different pressing forces could be established. Among the plant extract-based dye sensitised cells the ones sensitised with beetroot extract performed best. The cell that achieved the highest efficiency had a fill factor of 70%. Compared to the ruthenium-sensitised cells the overall performance of the plant dye sensitised cells were very poor and the produced photocurrents very low. The IPCE values were generally low: one of the best-performing cells had an IPCE value of slightly over 0.06 in the 440-470 nm wavelength ranges. One reason for this is that it is difficult to obtain a plant extract dye as intense and deep in colour as ruthenium complex-based dyes, since pigment saturation is obstructed by the presence of other chemical compounds in the plant extracts. Another is that it is a delicate and difficult matter to match the energy levels in the electrolyte-semiconductor system with the energy levels of the pigments in the plant extract dye.

The principles of dye-sensitized solar cells were studied and are outlined in this thesis. An overview of the basic steps needed to create a DSC isfollowed by detailed experimental information on how to assemble the solar cells that were fabricated in this project. They were based on synthesizednanocrystalline ZnO thin films sensitized by chlorophyll a as well as isolated photopigments from spinach leaves. The nanocrystals werestudied using XRD, and it was confirmed that three different methods of synthesis resulted in ZnO crystals of a few nanometers. The solar cellswere assembled with Au electrodes in a sandwich configuration and their photovoltaic properties were measured. Overall light-to-electricity conversionwas low with the highest efficiency being 0.21 %. An astonishingly low efficiency of 0.0003 % was noted for a thin film which was not thermallytreated, and it is suggested that heat-treatment is of great importance. It was also found that photopigments from spinach can be extractedeasily and used as molecular sensitizer without any demanding purification steps.

Based on the solar cell¡¦s four characteristic parameter open-circuit voltage (Voc) makes the discussion.The study of the relation VOC¡¦s paper uses empirical formula. VOC¡¦s formula is ¡§VOC=(1/e)(¡UEDonorHOMO¡W-¡UEAcceptorLUMO¡W)-0.3V¡¨. We can know that VOC related to donor material¡¦s HOMO and acceptor material¡¦s LUMO, if we need a high VOC, it can change the structure of donor material to have higher HOMO value, as well as the acceptor material have lower LUMO value. Our active layer except poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-Butyric acid methyl ester (PCBM), the third material was blended to discuss their effect on the VOC. Two kind of different bromined-P3HT (Br-P3HT) were used 40% and 100% bromined-P3HT to blend in active layer. Their Three materials blended under the different weight percent and the basic device configurations in this study was ITO / PEDOT : PSS / P3HT : Br-P3HT : PCBM / Al , efficiency was measured under AM 1.5G 100mW/cm2 illumination. When blended Br-P3HT(100%) in the active layer, VOC increased from 0.6V to 0.68V and the surface roughness makes short-circuit current and fill factor, increased make lower power conversion efficiency. When blended Br-P3HT(40%) into the active layer, not only can increase VOC to 0.66V, but influence the short-circuit current and the fill factor. The power conversion efficiency changed from 2.20% to 2.46%.

Dye-sensitized solar cells (DSSCs), based on use of a black counter electrode (BCE) and thin TiO2 electrode (photoelectrode), have been developed to reduce related manufacturing costs. Despite their effectiveness in lowering manufacturing cost, the above DSSCs have a low photovoltaic performance, owing to their insufficient light harvesting efficiency. This work presents a novel metal-based light scattering layer (MLSL), which can be formed either on a black counter electrode or on a thin TiO2 electrode, to reflect the light passing through the latter. The proposed MLSL increases the light harvesting efficiency from the interior of the cell, thus enhancing the photovoltaic performance of DSSC. Experimental results indicate that the proposed MLSL also reduces the internal resistance, as well as increases the electron collection efficiency of DSSC, subsequently increasing the power conversion efficiency by 116%. This work also designs a low-cost external lightguide (EL), which is disposed on the exterior of photoelectrode of DSSC, to direct light towards the dye-covered nanoporous TiO2 film (D-NTF) of the photoelectrode. Incorporating EL can increase the light harvesting efficiency from the exterior of the cell, thus enhancing the photovoltaic performance of DSSC. Furthermore, in addition to increasing the light harvesting efficiency by 30.69%, the proposed EL increases the photocurrent density by 38.12% and power conversion efficiency by 25.09%.

Transition metal oxides having high dielectric constants and wide band gaps find very important and interesting technological applications in surface physics. In particular, titania is the most commonly used material in heterogeneous catalysis because of its stable and flat surfaces. Having Ti cations at different charge states within the system brings about various novel electronic properties which are mainly surface related. Adsorption of catalytically important or chemically useful molecules on titania surfaces are investigated, electronic energy bands and charge densities are calculated from first principles using the density functional theory in the GGA scheme. The comparisons with the leading theories and existing experimental data are maid.

Direct conversion of solar energy, which is the most powerful and unlimited one among the renewable energy sources / into the electrical energy by the photovoltaic devices, is a promising way of meeting the energy needs of future. Thin film semiconductor materials show great promise for the production of efficient, low-cost solar cell devices. Recently advanced research on thin film photovoltaics in all aspects, has attracted intense attention. Thin film semiconductors for the photovoltaic applications are deposited in large areas by different methods. In this study, deposition and characterization of CuIn1-x GaxSe2 ( CIGS ) semiconductor thin films by thermal evaporation and e-beam evaporation methods were investigated. Material properties and deposition parameters of the thin films are aimed to be optimized for solar cell applications. Structural properties of the deposited CIGS thin films were examined through X-ray diffraction and Energy Dispersive X-ray Analysis. The temperature dependent electrical conductivity, Hall effect and photoconductivity of these samples have been measured between 100 and 400 K. For the optical characterization of CIGS thin films, the transmission measurements have been carried out in the wavelength region of 325-900 nm. The changes in the structural, electrical and optical properties of samples through post-depositional annealing effect were also analyzed.

Aim of this work is to construct dye sensitized solar cells employing core shell type nanocrystalline FTO/TiO2 photoanodes. Fluorine doped tin dioxide (FTO) nanoparticles were synthesized under hydrothermal conditions. Homogeneously precipitated SnO2 nanoparticles were dispersed in aqueous solutions containing NH4F as fluorine source and heat treated at 180oC for 24 hours. X-Ray analysis revealed that particles show rutile type cassiterite structure. Particles had 50 m2/g specific surface area measured by BET. Particle size was around 15-20 nm verified by XRD, BET and SEM analysis. Electrical resistivity of the powders measured with four point probe technique was around 770 ohm.cm for an F/Sn atomic ratio of 5, which showed no further decrease upon increasing the fluorine content of solutions. Thick films were deposited by screen printing technique and SEM studies revealed that agglomeration was present in the films which decreased the visible light transmission measured by UV-Visible spectrophotometry. TiO2 shell coating was deposited by hydrolysis of ammonium hexafluorotitanate and TiCl4 aqueous solutions. Efficiency of FTO nanoparticles was enhanced upon surface treatment where best result was 4.61 % for cells treated with TiCl4. Obtained photocurrent of 22.8 mA/cm2 was considered to be very promising for the future work. Enhancement v in efficiency was mostly attributed to suppressed recombination of photoelectrons and it is concluded that improved efficiencies can be obtained after successful synthesis of FTO nanoparticles having lower resistivity values and deposition of homogeneous shell coatings.

Solar cell production has served as the most important link in solar photovoltaic¡]PV¡^ supply chain from upstream silicon raw material and wafer supply to downstream module and system installation. The PV industry enjoyed a miraculously rapid growth in recent years with Taiwan ranking No. 4 in global solar cell production in 2008. However, in the wake of the financial storm, the industry has gone through some unprecedented changes in the market due to the severe global demand shrinkage. Looking ahead, challenges also lie in product assimilation and profit erosion. Difficulty will increase with market concentration and global operation; while the low yield of capital investment in R & D in the new industry adds on the pressure, too. This thesis proposes a four-step global development strategy for Taiwan solar cell industry after a SWOT analysis. Producers are advised to exert current strengths in developing tolling business in the short term for elevating uptime and capacity, while, in the long run, they should coordinate more efforts in brand-building and innovation for differentiation. Efforts should also be persisted to strengthen linkage within the supply chain and to extend ties with the government, end market, or other industries to create better synergy. Meanwhile, the government is expected to provide incentives for strategic research, to assist in cross-business alliance with Taiwan leading IT technologies and to bridge between the two sides of the Taiwan Straits for enhanced cooperation in solar PV industry, to ensure Taiwan¡¦s firm grip in the rising industry of global alternative energy.

The overall goal of this research is to improve fundamental understanding of the hydrogen passivation of defects in low-cost silicon and the fabrication of high-efficiency solar cells on thin crystalline silicon through low-cost technology development. A novel method was developed to estimate the flux of hydrogen, released from amorphous silicon nitride film, into the silicon. Rapid-firing-induced higher flux of hydrogen was found to be important for higher defect passivation. This was followed by the fabrication of solar cell efficiencies of ~ 17% on low-cost, planar cast multicrystalline silicon. Solar cell efficiencies and lifetime enhancement in the top, middle, and bottom regions of cast multicrystalline silicon ingots were explained on the basis of impurities and defects generally found in those regions. In an attempt to further reduce the cost, high-efficiency solar cells were fabricated on thin crystalline silicon wafers with full area aluminum-back surface field. In spite of loss in efficiency, wafer thinning reduced the module cost. Device modeling was performed to establish a roadmap towards high-efficiency thin cells and back surface recombination velocity and back surface reflectance were identified as critical parameters for high-efficiency thin cells. Screen-printed solar cells on float zone material, with efficiencies > 19% on 300 μm and > 18% on 140 μm were fabricated using a novel low-cost fabrication sequence that involved dielectric rear passivation along with local contacts and back surface field.