The effects of morphology on electronic and optical properties in solution processable photovoltaic (PV) materials have been studied through two different approaches. One approach, scanning photocurrent (PC) and photoluminescence (PL) microscopy, involved mapping PC generation and PL in functional PV devices on the length scale of around 250-500 nm. Additionally, local diode characteristics were studied from regions of interest in the PV through local voltage-dependent photocurrent (LVPC) measurements. In a PV made from a Copper Indium Gallium Selenide (CIGS) nanocrystal (NC) "ink", two morphological features were found to cause the spatial heterogeneity in PC generation. Cadmium Sulfide (CdS) aggregates lowered PC generation by blocking incident light to the photoactive layer, and cracks in the CIGS-NC film enhanced PC generation through improved charge carrier extraction. LVPC measurements showed all regions to have similar diode characteristics with the main difference being the PC generated at zero bias voltage. For another PV made from a donor/acceptor blend of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,Nphenyl- 1,4-phenylenediamine (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT), two incident laser wavelengths were used to selectively illuminate only one or both polymers. The results showed that when F8BT is illuminated, the PFB-rich regions produced the most PC and when both polymers are illuminated (but mostly PFB), the F8BT-rich regions produce the most PC; showing PC generation is more affective when less absorber material is present in the morphology. The other approach to study morphological effects on PV properties was to fabricate particles that mimicked morphological variations known to occur in solution-processable PVs. Through solution processing of an oligothiophene molecule, a range of weakly coupled H-aggregate particles were made. These particles, identifiable by shape, were shown to have a varying degree of energetic disorder (as gauged by the 0-0 vibronic band intensity in the emission spectrum), despite all particles showing a similarly high degree of molecular order from fluorescence dichroism (FD) measurements. A trend was observed correlating a decrease in energetic disorder with an increase in the local contact potential (LCP) difference as measured with Kelvin probe force microscopy (KPFM). The LCP difference was found to range by 70 mV between particles of moderate to low energetic disorder.

In this thesis CIGS absorber layers have been deposited by gas flow sputtering with an extra supply of selenium, a method that displays promise for large scale production because of its one-step sputtering route which deposits low energy particles in a high deposition rate. In this thesis a method was developed where selenium was added to the sputtering process inside the sputter chamber in a controllable manner and in larger amount than done in previous projects. A total of five samples were manufactured with altered evaporation temperatures and an extra supply of selenium which then were finalized to solar cells using the standard baseline process of the Ångström solar center. The characteristics of the CIGS layer and solar cells were analyzed by XRF, IV- and QE measurements. A cell with a conversion efficiency of 11.6 %, Jsc of 27.9 mA/cm2, Voc of 0.63 V and fill factor of 66.2 % was obtained on a 0.5 cm2 cell area without an antireflective coating. All samples contained cells with obtained efficiencies above 10 %, but over the whole samples the efficiencies varied considerably. The samples that were deposited with moderately large selenium evaporation provided the highest efficiencies with a relatively good homogeneity over the substrate. Results show a deficiency of copper in the CIGS films compared to the target composition. The copper content was lower than 70 % expressed in Cu/(Ga+In), which probably resulted in a low diffusion length for electrons, leading to limited cell efficiencies.  Through the duration of the thesis issues that concerned the power supply- and the controls to the substrate heaters as well as the control of the evaporation temperature during the depositions arose that required problem solving and needs to be resolved for the future progression of this work. The conclusions drawn from this thesis are that it is possible to vary the temperature of the selenium source and thereby control the amount of selenium that evaporates during the deposition process even though there is a lot of additional heating in the sputter chamber from both the substrate heaters and the sputter source which could affect the ability to control the amount of selenium being evaporated. That the most likely reason for the limited efficiencies is due to the low copper content in the CIGS films and that a larger amount of evaporated selenium compared to previous work did not result in higher obtained efficiencies.

Detta arbete syftade till att svara dels på vilka solcellstyper som finns på den svenska marknaden och vad som skiljer dem åt, dels hur förutsättningarna ekonomiskt ser ut för solceller i Sverige. Arbetets metod bestod av en litteraturstudie och en marknadssammanställning. Resultatet visade på att solceller finns etablerade på den svenska marknaden och att det är monokristallina och polykristallina kiselsolceller som dominerar utbudet. Kiselceller har fördelen att grundämnet finns i stor koncentration på jorden men de kräver en energikrävande process för tillverkningen. Vidare visade resultatet att en mindre del av marknaden utgörs av tunnfilmssolceller av CIGS och CdTe. Tunnfilmerna har en tjocklek ned till en mikrometer och har en tillverkningsprocess som är enklare och mindre energikrävande. Förutsättningarna för solceller i Sverige är betydligt sämre än för sydligare länder och även inom Sverige varierar förutsättningarna stort. Endast med hjälp av flera subventioner kan solceller i mindre skala göras ekonomiskt hållbara idag. / The purpose of this paper was to examine which types of solar cells are available on the Swedish market, their technical properties and the economic conditions for photovoltaics in Sweden. The method consisted of a literature study and a market survey. The result showed that photovoltaics are well established on the Swedish market and that it is monocrystalline and polycrystalline silicon solar cells which dominate. Silicon cells have the advantage of an unlimited supply of the chemical element. However the manufacturing process is an energy consuming. Furthermore, the results showed that a small part of the market is made up of thin film solar cells of CIGS and CdTe. Thin films have a thickness down to a micrometer and the manufacturing process is easier and less energy consuming. The condition for photovoltaics in Sweden is less favorable than in countries situated further south. The prerequisite also varies largely in Sweden. Only with the help of subsidies may photovoltaic on a smaller scale be made economically viable today.

CIGS thin film solar cells usually include a thin layer of intrinsic zinc oxide (i-ZnO) deposited on a CdS buffer layer by sputtering. However an interest has grown in using chemical vapor deposition (CVD) instead. Hence, the aim of this thesis was to study how well CVD i-ZnO performs on a CdS buffer layer in a CIGS solar cell and how the properties of the layer can be controlled when using a hot-wall CVD reactor with diethylzinc and water as precursors. The process was characterized through depositions on glass substrates and was then successfully implemented in solar cell devices. The main influences of temperature, thickness and precursor flows on resistivity, optical band gap and film structure were mapped out. The analysis methods used included X-ray diffraction (XRD), X-ray fluorescence (XRF), four point probe resistivity measurements, mechanical profilometry and absorption spectrophotometry. In addition, the solar cell devices were characterized using external quantum efficiency (EQE) and current-voltage (IV) measurements. It was found that the CVD process was sensitive to the condition of the CdS surface, which resulted in a large distribution of shunted cells when grown on aged CdS. Unexpected trends in open-circuit voltage and fill factor were found. Both these factors increased when the growth temperature was decreased, resulting in higher conversion efficiencies. Compared to i-ZnO deposited by an in-house baseline sputtering process, the CVD process resulted in cells with higher short-circuit current due to higher EQE in the short-wavelength region. It was shown that the CVD process used is capable of producing solar cell devices whose performances contest those of cells manufactured with sputtered i-ZnO.

It is essential to make performance measurements of photovoltaics modules in order to quantify the power they will produce under operational conditions. Performance measurements are fundamental throughout the photovoltaic industry, from product development to quality control in manufacturing and installation in the field. Rapid and economic evaluation of photovoltaic performance requires measurements using pulsed illumination solar simulators. However some devices have characteristics which can cause difficulties making these measurements. The aim of this thesis is to overcome these measurement problems focusing particularly on two of the most prevalent and pressing of these problematic characteristics: high capacitance and metastability. A new method for measuring high capacitance modules in a pulsed simulator, based on tailor made voltage ramps, was developed. The voltage ramp is tailor made such that the measurement time is minimised while maintaining high accuracy (0.5 %), allowing the measurement of high capacitance modules in a single 10ms illumination pulse. The necessary inputs for this method are the capacitance and dark current as a function of voltage for each module. In order to make these measurements, at the high forward bias voltages required, a new system was developed. The tailored voltage ramp can be created individually for each module, since the process is rapid an automatic. This makes the method applicable to a production line or to test house measurements. In addition to their use as inputs for the voltage ramp design, the capacitance and dark current also contain other valuable information, including effective minority carrier lifetime. In several thin film technologies, such as CIGS, the efficiency is not a fixed value, rather the module is metastable and the efficiency changes depending on the previous exposure /preconditioning of the device. Preconditioning is normally applied to these devices before measurement in order to put them in a specific state that is repeatable and representative of outdoor operation. Improved preconditioning practices are vital for performance measurements in CIGS modules. Therefore the preconditioning behaviour of a variety of CIGS modules from different manufacturers was investigated. The effect of preconditioning varied for different modules, commonly the fill factor improved substantially, but often changes in open circuit voltage were also seen and in some cases also substantial changes in short circuit current. The rates of preconditioning and relaxation were found to follow stretched exponential behaviour, such that the changes occur linearly on a logarithmic timescale over several orders of magnitude in time. The total time for performance stabilisation was found to vary significantly between different types of module. Because of this stretched exponential behaviour, even though the module took days to fully relax to the dark state, there was significant relaxation within the tens of minutes that it would normally take a module to cool down after light soaking before it could be measured. The major implication of observed kinetics is that in order to achieve repeatable measurement the timing in each element of a preconditioning routine should be controlled such that the fractional error in the duration of each step is small. During the investigation an unexpectedly short timescale preconditioning effect was observed, which occurs on a millisecond timescale and relaxes in seconds. It was shown that the measurement artefacts introduced using this method can be eliminated by using electrical forward bias until immediately before the measurement. Another measurement system was developed to track the dark current and C-V characteristic of the modules during electrical bias preconditioning and subsequent relaxation. These measurements demonstrate that more than one process involved during preconditioning in CIGS. Changes occur both in the doping in the bulk of the absorber and also in charge accumulation occurring near to the absorber / buffer interface. The theoretical models for preconditioning in CIGS were reviewed and compared to the experimental results. A rate model was developed based on the theory of the metastable VSe-VCu defect. This model was shown to correspond well to the rates of preconditioning and relaxation in CIGS. The non-exponential behaviour was shown to be compatible with a distribution of activation energies for the transition between different defect states. The difference in the time taken for modules to stabilise is explained by differences in doping density and the density of VSe-VCu defects. The work presented facilitates more accurate, economical performance measurements for high capacitance devices and CIGS devices, thereby contributing to the large scale implementation of photovoltaics as power source.

Corduroy Jones is contacted by a local promoter to reunite his band Streetwise Preacher. Over a three week span, Corduroy and his bandmates Tony and Johnny go through a series of events leading up to their Halloween Night reunion show.

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