In this thesis I study the impact of electrification using solar photovoltaic panels in the rural Ecuadorian community of Las Balsas. Many large-scale development organizations like the World Bank promote small-scale renewable energy technologies like solar photovoltaics as being crucial in helping poor rural communities generate more income. My research however, both in the field and in the literature, shows income generation from these projects tends to be minimal. I find that the introduction of solar electrification is most important for social applications like music, movies, cell phones, and lighting. FEDETA, the NGO that installed the solar photovoltaics, promotes the development project not as a neoliberal market-based income-generation project, but rather as a humanistic improvement in the “quality of life” of local residents. I analyze this goal of the project in light of the development theories developed over the past few decades. I question how well solar photovoltaics fits into the “small is beautiful” appropriate technology sector. While solar photovoltaic systems have the potential to build small-scale islands of autonomous electricity production in a more environmentally sustainable manner than grid electricity based on fossil fuels, I caution that this is not necessarily the most equitable way to provide electricity to the rural poor in developing countries. While solar home systems have much potential to provide (often minimal amounts of) electricity to extremely rural areas, the service provided is in many cases inferior to grid electricity. While solar photovoltaic technology does provide many potential benefits in areas not reached by grid electricity, NGOs and policy makers should be wary of seeing the technology as a panacea for sustainable development. Solar photovoltaics as a technology has a long way to go to provide energy services comparable to that offered by most grid systems. As with any technology its actual use is not predetermined, but rather is influenced by the local social and cultural contexts. / text

While solar photovoltaic (PV) panels can offset fuel, emissions, and water use at the power plant, high levels of installed rooftop PV capacity can have negative impacts on the stability and efficiency of the local grid because of power factor (PF) degradation. Specifically, electric utilities have noted voltage fluctuations from solar PV that occur more dynamically than legacy, electromechanical voltage regulation solutions like capacitor banks are designed to correct. At the same time, distributed power electronics devices like inverters can provide the type of dynamic voltage support that utilities seek to maintain reliability while juggling load growth and a greening grid. Using data from Pecan Street Inc. Smart Grid Demonstration Project in Austin, Texas and Austin Water Utility (AWU), this research examines the potential for a three-phase, four quadrant variable speed drive (VSD) in the water sector to provide PF correction to a load pocket of 63 homes experiencing varying levels of PV penetration. In the analysis, the VSD is not reserved for voltage support; instead it is predominantly used to drive a 30 kilowatt (kW) centrifugal sewage pump. The simulation determines the degree to which the VSD can restore PF to a threshold of 0.95, slightly below the targeted value for Austin's electric utility. Further, the economic viability of using the VSD as a grid device is explored by comparing the per unit cost of the PF correction it provides to a current utility solution for dynamic voltage regulation. / text

The role of the oxide/organic and organic/organic interfaces in small-molecule planar-Heterojunction (PHJ) photovoltaics was investigated with three interrelated projects: i) indium-tin oxide (ITO) bottom contact electrodes were modified with gold nanoparticles (Au-NPs) to improve rates of charge-transfer at the donor/oxide interface, ii) donor layers in OPVs were textured to increase charge generation at the organic/organic' interface, and iii) the effect of co-facial overlap on device performance via tuning of the electron acceptor orientation at the organic/organic interface. The modification of ITO with Au-NPs showed increased performance in small-molecule OPVs when compared to non-processed ITO devices due to the interactions between the Au-NPs and the donor material. Textured TiOPc increased overall device performance by a factor of 2X via the increased surface area, near-IR absorption, and increased mobilities. Modified and un-modified PTCDA acceptors showed that co-facial overlap at the organic/organic' interface is a large determinant in device performance, while the performance in small-molecule planar-heterojunction photovoltaics were severely affected by the pre-treatment process, most likely due to the particular interactions between the oxide and the donor material.

Support for electricity generation from renewable energy sources is one of measures aimed at switch of European economies from fossil fuels to renewables. In the past a lot of attention was paid to the theoretical assessment of different support schemes, however, analysis of the empirical data on those schemes is somewhat lacking. This thesis analyses assessment of two types of support schemes in three countries on empirical data. The main contribution of this work is (i) expansion of previously used methodology that analyses relationship between investments into electricity generation from renewable energy and the net present value of such investments, and (ii) inclusion of the Czech Republic into the list of observed countries. JEL Classification E61, O31, O33, O38, Q28, Q42 Keywords renewables, RES-E, photovoltaics Author's e-mail jbizek@gmail.com Supervisor's e-mail milan.scasny@czp.cuni.cz

This paper presents a segmented parabolic concentrator employing holographic spectral filters that provide focusing and spectral bandwidth separation capability to the system. Strips of low band gap silicon photovoltaic (PV) cells are formed into a parabolic surface as shown by Holman et. al. [1]. The surface of the PV segments is covered with holographic elements formed in dichromated gelatin. The holographic elements are designed to transmit longer wavelengths to silicon cells, and to reflect short wavelength light towards a secondary collector where high-bandgap PV cells are mounted. The system can be optimized for different combinations of diffuse and direct solar illumination conditions for particular geographical locations by controlling the concentration ratio and filtering properties of the holographic elements. In addition, the reflectivity of the back contact of the silicon cells is used to increase the optical path length and light trapping. This potentially allows the use of thin film silicon for the low bandgap PV cell material. The optical design combines the focusing properties of the parabolic concentrator and the holographic element to control the concentration ratio and uniformity of the spectral distribution at the high bandgap cell location. The presentation concludes with a comparison of different spectrum splitting holographic filter materials for this application.

Polymer photovoltaic systems whose photoactive layer is a blend of a semiconducting polymer with a fullerene derivative in a bulk heterojunction configuration are amongst the most successful organic photovoltaic devices nowadays. The three-dimensional organization in these layers (the morphology) plays a crucial role in the performance of the devices. Detailed characterization of this organization at the nanoscale would provide valuable information for improving future material and architectural design and for device optimization. In this thesis, the results of morphology studies of blends of several polyfluorene copolymers (APFOs) blended with a fullerene derivative are presented. Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy was combined with dynamic Secondary Ion Mass Spectrometry (dSIMS) for surface and in-depth characterization of the blend films. NEXAFS was performed using two different electron detection methods, partial (PEY) and total (TEY) electron yield, which provide information from different depth regimes. Quantitative compositional information was obtained by fitting the spectra of the blend films with a linear combination of the spectra of films of the pure components. In blends of APFO3 with PCBM in two different blend ratios (1:1 and 1:4 of polymer:fullerene) NEXAFS data show the existence of compositional gradients in the vertical direction for both blend ratios, with clear polymer enrichment of the free surface. A series of APFOs with systematic changes in the side-chains was studied and it was shown that those small modifications can affect polymer:fullerene interaction and induce vertical phase separation. Polymer-enrichment of the free surface was clearly identified, in accordance with surface energy minimization mechanisms, and a compositional gradient was revealed already in the first few nanometers of the surface of the blend films. dSIMS showed that this vertical phase separation propagates throughout the film. It was possible to determine that as the polar character of the polymer increases, and thus the polymer:fullerene miscibility is improved, the tendency for vertical phase separation becomes stronger. / <p>Paper II was not published at the time of the licentiate defence and had the title: NEXAFS spectroscopy study of the surface composition in APFO3:PCBM blend films</p>

Les cellules solaires comprenant comme matériau actif une pérovskite organométallique hydride sont apparues récemment comme une technologie de haute performance et bon marché pour la conversion de l’énergie solaire. Les efforts mobilisés pendant cette thèse se sont concentrés sur un composant clé des cellules solaires à pérovskite, le transporteur de trous, qui assure à la fois les performances et la stabilité des cellules. Les avantages des polymères semi-conducteurs pour cette fonction se retrouvent dans leur stabilité, leurs bonnes propriétés de transport de charge et leur caractère filmogène. Ainsi, la stabilité des cellules solaires à pérovskite planes a pu être améliorée en intégrant un polyvinylcarbazole fonctionnalisé, tout en conservant de bonnes efficacités. Le potentiel de polyélectrolytes à base de PEDOT a pu être évalué dans les cellules de type inverses. Et enfin, une nouvelle méthode de dopage par un polyélectrolyte à base d’imidazole a démontré des efficacités remarquables, supérieures à 20%. / Perovskite solar cells based on hybrid organometal perovskite recently appeared as a cost-effective and highly efficient technology for the conversion of sunlight. Efforts undertaken during this PhD thesis focused on one component of the perovskite solar cells, the hole transport material, which rules both, performance and stability of the devices. Advantages of semiconducting polymers result in their thermal and chemical stability, their good charge transport properties and their ability to form homogeneous thin films. Thereby, through synthesis of novel polyvinylcarbazole and incorporation into devices, stability of planar perovskite solar cells has been enhanced while conserving good efficiency. The potential of PEDOT-based polyelectrolytes has been investigated in inverted perovskite solar cells. Finally, a new strategy to efficiently dope hole transporting materials has been demonstrated through the introduction of N-heterocyclic imidazolium-based polyelectrolytes. Thereby, efficiency of solar cells has been promoted to over 20%.

Thesis advisor: Michael J. Naughton / Geometrically generalized analytical expressions for device transport are derived from first principles for a photovoltaic junction. Subsequently, conventional planar and unconventional coaxial and hemispherical photovoltaic architectures are applied to detail the device physics of the junction based on their respective geometry. For the conventional planar cell, the one-dimensional transport equations governing carrier dynamics are recovered. For the unconventional coaxial and hemispherical junction designs, new multi-dimensional transport equations are revealed. Physical effects such as carrier generation and recombination are compared for each cell architecture, providing insight as to how non-planar junctions may potentially enable greater energy conversion efficiencies. Numerical simulations are performed for arrays of vertically aligned, nanostructured coaxial and hemispherical amorphous silicon solar cells and results are compared to those from simulations performed for the standard planar junction. Results indicate that fundamental physical changes in the spatial dependence of the energy band profile across the intrinsic region of an amorphous silicon p-i-n junction manifest as an increase in recombination current for non-planar photovoltaic architectures. Despite an increase in recombination current, however, the coaxial architecture still appears to be able to surpass the efficiency predicted for the planar geometry, due to the geometry of the junction leading to a decoupling of optics and electronics. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Significant improvements in power conversion efficiency (>10%) of emerging thin-film photovoltaics have been achieved in the last 5 years. High efficiencies would not be possible without the development of new selective interfacial layers. However, a complete understanding of how interfacial layers function to improve the selectivity of charge extracting contacts in thin-film photovoltaics is still being sought. The goal of this work is to contribute to the understanding of the operation of selective interfacial layers based on the study of ionically functionalized fullerenes. Just as other ionically functionalized materials have shown promise as electron-selective interfacial layers in organic photovoltaics and mixed organic-inorganic halide perovskites, Chapter II demonstrates the utility of ionically functionalized fullerenes. High performing solar cells necessitate the use of conductive interfacial layers; anomalously high conductivity in ionically functionalized materials, which have been used as interfacial layers, has been ascribed to self-doping. This work demonstrates that less than 1% of an ionically functionalized fullerene is reduced in its highly conductive pristine state and is concurrent with the presence of distinct chemical species. These studies describe how the chemical origin of the high conductivity of ionically functionalized fullerenes does not require the invocation of direct anion reduction or significant chemical transformations such as Hofmann-like elimination reactions occurring to a stoichiometric degree. This work also addresses the question of how the selectivity of a charge extracting contact is improved by the presence of an interfacial layer. The quantification of energy barrier reduction, which is often discussed in terms of work function modification or energy-level alignment, is demonstrated using metal|semiconductor junctions modified with an ionically functionalized fullerene. The barrier height of high work function electrodes was reduced significantly, by as much as 0.45 V, and was correlated to thin (2–5 nm) portions of the film rather than fullerene aggregates. The studies that comprise this work form a coherent model for understanding the key factors that have resulted in the continued use of ionically functionalized interfacial layers, their high conductivity, and energy barrier modification of the charge extracting electrodes. This dissertation contains coauthored, previously published, and unpublished work. / 10000-01-01

Cu2ZnSnS4 (CZTS), being related to the highly successful Cu(In,Ga)(S,Se)2, and CuInS2 materials, is a promising candidate for thin film photovoltaic devices. It has the advantage that it contains no rare or expensive elements, and therefore has cost-reduction potential for commercial systems. A two-stage process for fabrication of CZTS films is presented, which consists of sequential electrodeposition of Cu, Sn and Zn layers followed by a heat treatment in the presence of S vapour (‘sulfurisation’). Electrodeposition conditions are developed to give uniform Cu|Sn|Cu|Zn precursors of controlled morphology and composition, by the use of a rotating disc electrode system. Precursors are converted to CZTS by sulfurisation in the presence of elemental S, using a rapid thermal processing system (RTP). The sulfurisation reaction is studied by XRD and Raman spectroscopy as a function of temperature and at short time intervals, and a sequence of reactions is derived for the formation of CZTS. It is shown that the sulfurisation reaction occurs within minutes above 500°C. A model is presented for film formation when rapid heating rates are employed. The effects of sulfurisation time, background pressure and precursor composition on the morphological and structural properties of the CZTS films are investigated. Observations of grain size changes and compositional modification are made and explained in terms of the likely secondary phases present. The opto-electronic properties of the CZTS films are measured using a photoelectrochemical technique. Changes in the external quantum efficiency and band gap are studied as a function of sulfurisation parameters and precursor composition. After crystallisation of the CZTS phase during sulfurisation, the photocurrent obtained from the films continued to rise upon heating in the absence of S, which is explained by changes in acceptor concentration. Large shifts in the band gap are seen, and some proposals are made to explain the behaviour. The observations are discussed in the context of the particular compositions and sulfurisation conditions routinely used in the CZTS literature, and recommendations are made for further work.