No description available.

No description available.

Semiconductor colloidal quantum dots have an interesting potential to increase solar cell efficiency, with strong absorption in the infrared region and a tunable band gap. In this work an attempt was made to adopt a manufacturing process for PbS quantum dot solar cells, proven successful at Uppsala University. Two optimizations were investigated and the stability of the quantum dot films was analyzed with regards to three storage conditions, varying oxygen accessibility and light exposure, and measured with UV-Vis spectroscopy and X-ray photoelectron spectroscopy. Functioning solar cells were obtained but with lower performance than the results from Uppsala. Optimizations were partly successful with regards to improved spreading of the EDT solution on the PbS quantum dot film using ethanol and methanol as solvents. No improved cell performance was observed by applying both QD films inside argon atmosphere, as opposed to only the first one. Clear differences in oxidization of the films and loss of iodine ligand could be identified for the different storage conditions, with best stability exhibited by films stored under argon atmosphere. / Kvantprickar av halvledande material har en intressant potential att förbättra solcellers verkningsgrad genom en stark absorption inom de infraröda spektrat och ett justerbart bandgap. I detta arbete gjordes ett försök att återskapa en tillverkningsprocess av kvantprickssolceller av PbS, som visat sig framgångsrik vid Uppsala universitet. Två optimeringar undersöktes och stabiliteten av kvantpricksfilmerna analyserades med avseende på tre förvaringsmiljöer med olika exponering för ljus och syre, och mättes med UV-visspektroskopi samt röntgenfotoelektronspektroskopi. Fullt fungerande solceller framställdes men med en lägre prestanda jämfört med resultaten i Uppsala. Optimeringarna var delvis lyckade gällande spridning av EDTlösningen på kvantpricksfilmen av PbS genom att använda etanol och metanol som lösningsmedel. Ingen förbättrad prestanda observerades hos cellerna genom att applicera båda kvantpricksfilmerna i argonatmosfär, jämfört med endast den första. Tydliga skillnader i oxidation för filmerna samt förluster av jodligand kunde identifieras för de olika förvaringsmiljöerna, med bäst stabilitet uppvisad av filmerna som förvarades i argonatmosfär.

This thesis addresses barriers to the widespread adoption of high-efficiency photovoltaic devices through the use of innovative semiconductor materials and device design. The feasibility of various strategies is explored through experimental characterization and modeling of semiconductor materials and devices. High-efficiency photovoltaic devices are made from epitaxially grown III-V semiconductor materials. Epitaxial devices are highly sensitive to lattice mismatch between the epi-layers and the substrate, requiring sophisticated substrate engineering or growth strategies to access materials outside of the lattice-matched regime. One promising strategy involves the electrochemical porosification of germanium on a lattice-mismatched silicon substrate to create a compliant interface for high-quality epitaxial growth of Ge, GaAs, and other equivalent-bandgap III-V semiconductors on silicon. This results in a threading dislocation density of ~10^4 cm^-2, a reduction of 4 to 6 orders of magnitude compared to direct epitaxy of germanium on silicon. This technology could enable the development of highly efficient III-V multi-junction photovoltaic devices on cost-effective silicon substrates that benefit from well-established commercial supply chains. In the first part, I present characterization of the electrical properties of porous germanium. Experimental measurements revealed conductivities ranging from 0.6 to 33 (x10^-3) Ohm^-1 cm^-1, depending on the morphology. The relationship between the electrical properties and the morphology is described using an electrostatic model that can be generalized to other porous semiconductors including silicon. For a compliant interface designed to integrate a standard triple-junction solar cell onto a silicon substrate, the porous Ge/Si layers are predicted to introduce < 0.01 Ohm cm^2 of series resistance to the device, which is sufficiently low for concentrated photovoltaic applications. Optoelectronic device modelling of the triple-junction solar cell on silicon demonstrates that III-V triple-junction solar cells fabricated on silicon using this compliant Ge/Si porous interface could achieve 93% of the efficiency of a comparable defect-free device. The remainder of this thesis is concerned with the design and characterization of photovoltaic devices optimized for monochromatic illumination, known as photonic power converters. Most commercially available photonic power converters are based on GaAs and are suitable for short-range photonic power transmission through optical fiber (< 1 km). Extended reach power-over-fiber systems require the use of photonic power converters that are compatible with longer-wavelength light, which travels further in optical fiber. One candidate material for this application is the semiconductor quaternary alloy InAlGaAs lattice-matched to InP for photonic power converter operation in the telecommunications O-band, near 1310 nm. I describe the design and characterization of multi-junction InAlGaAs/InP photonic power converters grown by molecular beam epitaxy, including the analysis of material properties and characterization of single- and dual-junction devices under 1319-nm laser illumination. Optically thick devices are found to be diffusion-limited and device simulations suggest that non-radiative recombination is significant. The performance of InAlGaAs tunnel diodes, which act as interconnections for the absorbing junctions within a multi-junction device, is demonstrated to be highly dependent on the growth temperature, with peak tunneling current densities exceeding 1200 A/cm^2 in the best measured devices. In addition to molecular beam epitaxy-grown InAlGaAs/InP devices, I also characterize single-junction O-band photonic power converters grown by metal-organic vapour phase epitaxy with two alternative absorber materials. A lattice-matched InGaAsP/InP device is compared to a more cost-effective lattice-mismatched GaInAs device grown on GaAs using a metamorphic buffer layer. Both devices are measured under 1319-nm laser illumination with a variety of beam sizes and peak efficiencies of 52.9% and 48.8% were measured for the InGaAsP/InP and the metamorphic-GaInAs/GaAs devices respectively. At illumination powers exceeding 100 mW, the performance begins to degrade with increasingly non-uniform illumination, indicating that illumination profiles should be as uniform as possible to maximize device performance.

No description available.

Software for simulating the expected power production of photovoltaic installations is an important tool for monitoring the system condition. The purpose of this paper is to investigate modeling parameters and long term condition of existing up-and-running installations by using the software PVcheck. An evaluation of the software will be made with the intent of providing feedback that can be used to improve its functions. Central results in this paper include the proof of concept that a degradation analysis of photovoltaic installations can be made using PVcheck as well as showing an unexplained seasonal periodicity in results when using the Ineichen/Perez clear sky model in Glava, Sweden.

Detta kandidatexamensarbete utvärderar och jämför en befintlig solcellsanläggning med installerat energilager samt en smart växelriktare i Farsta, Stockholm. Jämförelsen ställer denna anläggning mot ett konventionellt solcellssystem med enbart solceller. Studiens syfte är att identifiera mängden egenanvänd solenergi, ta fram optimeringsförslag samt belysa eventuella kostnadsbesparingar. Den smarta växelriktaren har möjliggjort datainsamling via en webbaserad användarportal, portalen loggar och sparar anläggningens energi- och effektdata.   Studien påvisar att systemet inte bidrar med en betydande ökning av egenanvändningen av solenergi, ty batteriets inställningar ofta medför att batteriet är fulladdat under dagens soltimmar. Det smarta systemets mest fördelaktiga funktion är att kapa fastighetens effekttoppar vilket skapar möjlighet till nedsäkring.   Hur stor del av effekttopparna som kan kapas är starkt beroende av batteriets inställningar. Under studien har två olika scenarier testats. Det mest essentiella är att batteriet alltid kan kapa de högsta effekttopparna samtidigt som det aldrig laddas ur helt. Nyttan maximeras när batteriet aktiveras vid förbrukningar över 24 kW. Säkringsanalyserna från studien visar att fastighetens minsta möjliga huvudsäkringar som kan brukas är 35 A, dock rekommenderas nyttjande av huvudsäkringar om 50 A då en säkerhetsmarginal är önskvärd. Den rekommenderade nedsäkringen ger möjlighet att teckna ett billigare elavtal. Slutsatsen är att säkringsabonnemanget TID relativt effektabonnemanget L0,4S ger en kostnadsbesparing om 33 547 kronor per år. / This bachelor thesis is evaluating and comparing an existing photovoltaic system including an energy storage and a smart bidirectional converter in Farsta, Stockholm. This smart system will be compared with a conventional PV plant. The aim of the report is to identify the amount of self-consumed solar energy, give optimizing suggestions and shed light on possible cost savings. The smart converter has given the possibility to collect data from a web-based portal. The portal logs and stores the energy and power data of the system.   The study proves that this smart system does not contribute with an increased amount of self-consumed solar energy, since the battery settings implies a fully charged battery during the day. The most advantageous benefit in the smart system is to cut power peaks, which gives opportunities to use smaller main fuses in the real estate.   The magnitude of the power peaks that can be reduced is depending on the settings of the battery. Two different scenarios have been examined in the study. The most essential is that the battery is always able to cut the highest power peaks without being fully discharged. The maximum utility occurs when the battery is activated when the consumption is higher than 24 kW. Fuse analysis proves that the lowest possible main fuses that could be used in the real estate is 35 A. Though, this study recommends main fuses of 50 A since a safety margin is desired. This gives opportunities to sign a more beneficial electricity contract. Conclusively, the fuse rating contract that can be used is 33 547 SEK cheaper per year than the power rating contract that is used in the real estate today.

Functional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without increasing parasitic absorption within the anti-reflection coating(s); (2) to maximize internal back reflectance of rear passivated cells, thereby increasing optical absorption of weakly absorbed long wavelength photons (? > 900 nm); (3) to minimize recombination losses by providing excellent surface passivation; and (4) to improve doping processes during cell manufacturing (e.g., emitter and surface field formation) by functioning as highly controllable dopant sources compatible with in-line diffusion processes. The oxide materials deposited by APCVD include amorphous and polycrystalline titanium oxide, aluminum oxide, boron-doped aluminum oxide, silicon oxide, phosphosilicate glass, and borosilicate glass. The microstructure, optical properties, and electronic properties of these films are characterized for different deposition conditions. Additionally, the impact of these materials on the performance of different types of c-Si solar cells is presented using both simulated and experimental current-voltage curves.

This dissertation presents simulation tools developed specifically for the design of solar array power systems. Contributions are made in several aspects of the system design phases, including solar source modeling, system simulation, and controller verification. A tool to automate the study of solar array configurations using general purpose circuit simulators has been developed based on the modeling of individual solar cells. Hierarchical structure of solar cell elements, including semiconductor properties, allows simulation of electrical properties as well as the evaluation of the impact of environmental conditions. A second developed tool provides a co-simulation platform with the capability to verify the performance of an actual digital controller implemented in programmable hardware such as a DSP processor, while the entire solar array including the DC-DC power converter is modeled in software algorithms running on a computer. This "virtual plant" allows developing and debugging code for the digital controller, and also to improve the control algorithm. One important task in solar arrays is to track the maximum power point on the array in order to maximize the power that can be delivered. Digital controllers implemented with programmable processors are particularly attractive for this task because sophisticated tracking algorithms can be implemented and revised when needed to optimize their performance. The proposed co-simulation tools are thus very valuable in developing and optimizing the control algorithm, before the system is built. Examples that demonstrate the effectiveness of the proposed methodologies are presented. The proposed simulation tools are also valuable in the design of multi-channel arrays. In the specific system that we have designed and tested, the control algorithm is implemented on a single digital signal processor. In each of the channels the maximum power point is tracked individually. In the prototype we built, off-the-shelf commercial DC-DC converters were utilized. At the end, the overall performance of the entire system was evaluated using solar array simulators capable of simulating various I-V characteristics, and also by using an electronic load. Experimental results are presented.

The development of devices with high efficiencies can only be attained by tandem structures which are important to the advancement of thin-film photoelectrochemical (PEC) and photovoltaic (PV) technologies. FSEC PV Materials Lab has developed a PEC cell using multiple bandgap tandem of thin film PV cells and a photocatalyst for hydrogen production by water splitting. CdS/CdTe solar cell, a promising candidate for low-cost, thin-film PV cell is used as one of the thin film solar cells in a PEC cell. This research work focuses on developing various back contacts with good transparency in the infrared region (~750 - 1150 nm) for a CdS/CdTe solar cell. CdS/CdTe solar cells were prepared with three different configurations, Glass/SnO2:F/CdS/CdTe/ZnTe:Cu/ITO/Ni-Al (series 1), Glass/SnO2:F/CdS/CdTe/Cu2Te/ITO/Ni-Al (series 2), Glass/SnO2:F/CdS/CdTe/Br-Me etching/Cu/ITO/Ni-Al (series 3). The back contact preparation process for a CdS/CdTe solar cell involves the deposition of a primary p-type back contact interface layer followed by the deposition of transparent and conducting ITO and a Ni-Al outer metallization layer. Back contact interface layers were initially optimized on glass substrates. A ZnTe:Cu layer for a series 1 cell was deposited using hot wall vacuum evaporation (HWVE). Cu2Te and Cu thin films for series 2 and series 3 cells were deposited by vacuum evaporation. HWVE technique produced highly stoichiometric ZnTe:Cu thin films with cubic phase having {111} texture orientation. All the back contact interface layers demonstrated better transparency in the infrared region on glass substrate. Formation of crystalline phase and texture orientation were studied using X-ray diffraction (XRD). The composition was analyzed by electron probe microanalysis (EPMA). Transparency measurements were carried out by optical transmission spectroscopy. Thickness measurements were carried out using a DEKTAK surface profile measuring system. Finally, completed solar cells for all the series were characterized for current-voltage (I-V) measurements using the I-V measurement setup developed at the FSEC PV Materials Lab. The PV parameters for the best series 1 cell measured at an irradiance of 1000 W/m2 were: open circuit voltage, Voc = 630 mV, short circuit current, Isc = 7.68 mA/ cm2, fill factor, FF = 37.91 %, efficiency, ç = 3.06 %. The PV parameters for the best series 2 cell measured were: Voc = 690 mV, Isc = 8.7 mA/ cm2, FF = 45.19 %, ç = 4.8 %. The PV parameters for the best series 3 cell measured were: Voc = 550 mV, Isc = 9.70 mA/ cm2, FF = 42.25 %, ç = 5.63 %. The loss in efficiency was attributed to the possible formation of a non-ohmic contact at the interface of CdTe and back contact interface layer. Decrease in the fill factor was attributed to high series resistance in the device.