With scarce the energy source and the worsened environment pollution, how to create and use a clean and never exhausted energy is becoming very important day by day. This thesis we proposed the research and development of a solar energy storage system with fuzzy logic control. This solar energy storage system is composed of the solar cell, charger, batteries, buck converter and digital a signal processor. The solar energy storage charging system charger is based on buck circuit control with battery cycle pulse charging. with the fuzzy control theory combined in the tactics of charging , it¡¦s can improve the efficiency of charging, suppress the abnormally battery temperature rise, lengthen the battery¡¦s life, and reduce the waste used. In the experiment, four different charging methods, with the same starting voltage, are compared in terms of temperature control. Among the four methods, the fuzzy logic control proposed in this thesis is able to control the battery temperature at a good 30 Celsius Degree. Experimental and simulation results demonstrate the effectiveness and validity of the system.

For organic solar cells: exciton generation, exciton diffusion, charge transfer, and charge transport of a photoactive layer are the important factors in photocurrent generation. In this thesis, we blend small molecular material tris(8-hydroxyquinoline)aluminum (Alq3) into poly [ 2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene ]:short-length carbon nanotubes (MEH-PPV:SLCNTs) films to increase the light absorption, in the range of 300 to 450 nm, and hence increase the exciton generation. The comparison of the photoluminescence (PL) of a donor with that of the Donor-Acceptor composite provides an important and simple method to detect the charge transfer phenomenon. Furthermore, the degree of photoluminescence quenching may be representative of the efficiency of charge transfer. [1-6] Using this concept and method, we obtain that at the mix ratio of 1:0.5 (MEH-PPV:SLCNTs) by weight, 33 wt.% SLCNTs, probably have the maximum of charge transfer efficiency. To further check that at this concentration might have the maximum efficiency of the charge transfer, we also used time-resolved fluorescence spectrometer to measure the fluorescence lifetime of MEH-PPV. The shortest MEH-PPV fluorescence lifetime of 0.15 ns at 33 wt.% SLCNTs corresponds with our conjecture. For simplicity to discuss next experiment results, we make two assumptions at this mix ratio: (1) The efficiency of the charge transfer process is very high, so the competing processes can be neglected. Because of the forward electron transfer process occurs in the sub-picosecond time domain; (2) The exciton diffusion efficiency is approximately unity in the bulk heterojunction photoactive layer. Based on this assumption, the higher degree of photoluminescence quenching of MEH-PPV:Alq3 and MEH-PPV:Alq3:SLCNTs system demonstrates blending alq3 into MEH-PPV:SLCNTs films maybe can increase the charge photogeneration. The PL and UV/VIS absorption spectra are employed to examine the energy transfer process between Alq3 and MEH-PPV. When MEH-PPV:Alq3 films are excited at the wavelength of 380 nm which is in the main absorption region of Alq3, the increase in PL intensity of MEH-PPV at 577nm and the absent emission spectra of Alq3 illustrates Alq3 transfer its energy to MEH-PPV. By scanning electron microscopy, we observed that the surface pinholes became less than that of MEH-PPV films. This result suggests the devices utilizing the MEH-PPV:Alq3 composites as electron donor materials may have smaller electrode contact resistance. From all above the experiment data, we believe using MEH-PPV:Alq3:SLCNT as a photoactive layer perhaps can enhance the device performance.

A simple and high efficient wet etching technique for fabricating pyramid textures on (100) Si wafer is proposed. Conventionally, pyramid textures were formed on Si wafers to reduce reflections using KOH anisotropic etching. Isopropyl Alcohol (IPA) is often added to the solution to abate the bubbling effect caused by hydrogen released form the Si surfaces during reaction. In this study, a metal net with proper opening dimension was used as a shelter to trap the hydrogen from leaving the surfaces of Si, and therefore turns the hydrogen gas into a gas-type etching mask during the anisotropic etching. In this way, pyramid textures with dimensions range from 3µm to 8µm were successfully fabricated. The measured average reflectivity of the texture for incident optical wave length from 400nm to 1000nm is less than 18%.

We attempted to fabricate the CuInSe2:Sb thin-film solar cells with a Al/ZnO:Al(AZO)/ ZnSe /CuInSe2:Sb /Mo/soda-lime glass(SLG) structure. The growth of CuInSe2 film in the presence of Sb can effectively improve the surface morphology and benefit the growth of the device. A ZnSe buffer layer has been applied as an attractive alternative to a CdS buffer layer, thus eliminating environment from pollution. By varying the Ar pressure during the deposition, the Mo bilayer has been fabricated with both low resistivity and good adhesion. Currently the tensile stress was maintained below 100MPa, and the lowest sheet resistance achieved 0.205(£[/¡¼). The fabrication condition with a 5-cm sputtering distance could provide the lowest resistivity of 1.73¡Ñ10-3 (£[-cm) in the AZO thin-film that shows a transmittance of above 80¢Min the visible range. Applying the technology of optical lithography to deposit the Al metal front grid, the Al/ AZO ohmic contact resistance was improved. The energy conversion efficiency of the CIS thin-film solar cell (Al/ AZO/ ZnSe /CuInSe2 /Mo/ SLG) was 4.4¢M(Voc =0.41 V¡AI sc = 3.9 mA ¡AFF = 69 ¢M) by applying the irradiation with a solar simulator under one-sun (AM1.5, 100mW/cm2) conditions. However, the efficiency of CIS:Sb solar cell (Al/ AZO/ ZnSe /CuInSe2 :Sb /Mo/ SLG) was improved to to 6.0¢M(Voc =0.43 V¡AI sc = 5.15 mA ¡AFF = 68 ¢M). This result indicates that the CIS film growth with Sb can increase the short-circuit current.

Silicon heterojunction solar cells, a-Si:H/c-Si, are promising technology for future photovoltaic systems. An a-Si:H/c-Si heterojunction solar cell combines the advantages of single crystalline silicon photovoltaic with thin-film technologies. This thesis reports a detailed survey of heterojunction silicon solar cells with p-type wafer fabricated by magnetron sputtering and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques at low processing temperature. In the first part of this study, magnetron sputtering method was employed to fabricate a-Si:H thin films and then a-Si:H/c-Si solar cells. Amorphous silicon (a-Si:H) films were grown on glass in order to perform electrical and optical characterizations. The J-V characteristics of the silicon heterojunction solar cells were analyzed as a function of a-Si:H properties. It was shown that a-Si thin films with well-behaved chemical and electronic properties could be fabricated by the magnetron sputtering. Hydrogenation of the grown film could be achieved by H2 introduction into the chamber during the sputtering. In spite of the good film properties, fabricated solar cells had poor photovoltaic parameters with a low rectification characteristic. This low device performance was caused by high resistivity and low doping concentration in the sputtered film. The second part of the thesis is dedicated to heterojunction solar cells fabricated by PECVD. In this part a systematic study of various PECVD processing parameters were carried out to optimize the a-Si:H(n) emitter properties for the a-Si:H(n)/c-Si(p) solar cell applications. In the next stage, a thin optimized a-Si:H(i) buffer layer was included on the emitter side and on the rear side of the c-Si(p) to improve the surface passivation. Insertion of an a-Si:H(i) buffer layer yielded higher high open circuit voltage (Voc) with lower fill factor. It was shown that high Voc is due to the efficient surface passivation by the front/rear intrinsic layer which was also confirmed by the measurement of high effective lifetime for photo-generated carriers. Low fill factor on the other hand is caused by increasing resistivity of the solar cells by inserting low conductivity a-Si:H(i) layers.

Polymers are with low carrier mobility. If polymer solar cells are to exhibit high power conversion efficiencies, their carrier mobilities must be improved. Metallic NPs are promising materials for use in polymer solar cells because of their high conductivities. In this work, we studied the carrier transport characteristic of metallic nanoparticle blending into polymers. We blended Pt nanoparticles (Pt NPs) and Pd nanoparticles (Pd NPs) into polymers to improve carrier mobility, and enhance the power conversion efficiency of the polymer solar cell. P3HT was used as a donor material because of its high stability and with high absorption in visible light. PCBM was used as a acceptor material because of its high stability and with high electron transportation. We blended modified Pt NPs and Pd NPs into the P3HT:PCBM active layer, with the device configurations of ITO/PEDOT:PSS/P3HT:PCBM: Pt NPs/Al and ITO/PEDOT:PSS/P3HT:PCBM:Pd NPs/Al, respectively polymer solar cells measured was under AM 1.5G 100mW/cm2 illumination. When we blended Pt NPs into the active layer, the open-circuit remained 0.64V, the short-circuit current increased from 6.67mA/cm2 to 9mA/cm2, the power conversion efficiency increased from 1.96% to 3.08%. When we blended Pd NPs into the active layer, the open-circuit remained 0.62V, the short-circuit current increased from 6.33mA/cm2 to 7.33mA/cm2, the power conversion efficiency increased from 1.7% to 2.48%. The enhanced efficiency originated from the increased carrier mobility of the active layer when the Pt NPs or Pd NPs were present.

P3DDT (3-dodecylthiophene-2,5-diyl) and PCBM( [6,6]-phenyl C61-butyric acid methyl ester) were fabricated to the active layer of Bulk Heterojunction Organic Solar Cells .We obtained the device efficiency was 0.64 % by evaporating solvent at room temperature. We measured Thermal decomposition Temperature (Td) of P3DDT was 487¢J. But operational temperature was over 90¢J, it could affect the roughness of thin film and make efficiency to be 4¡Ñ10-3(%). For results of experiments, we know that roughness changed by the crystallization of side chain and exciton dissociation modified by the morphology between P3DDT and PCBM. Thin film solar cell has a large effect on the formation of active layer, such as heat treatment, choices of solvents, composition ratio, and speed of spin coating. The efficiency of solar cell has been shown to be highly sensitive to the size, composition and crystallization of the formed domains. We studied two kinds of conjugated polythiophenes with the same main chain but different side chain. When the number of carbon atoms of alkyl side chains is more than 10, some orderly arrangements will occur for side chains between the layers. We tried to explain the crystallization caused by long alkyl side chains determined which intrinsic phenomena are the most evident for altering the PCE of solar cell. After recrystallization, the layered structures of P3DDT can be improved, but those orderly degrees of the arrangements with PCBM are further aggregated. The main point for low PEC and Jsc by heat treatment is the unfavorable and roughened morphology. Charge transfer only occurs at the boundary ,which is interfacial area between donor and acceptor materials, hence, the low Jsc could be caused by poor charge transfer between P3DDT and PCBM. The redistributed arrangement of P3DDT domains exclude PCBM from original space, and it makes PCBM to aggregate large particles, from nanophase to mesophase scales, which reduce mutual solubility to be the source of PCE and Jsc reduction.

In this study, we deposit titanium dioxide (TiO2) on the indium tin oxide (ITO/glass) substrate by a liquid phase deposition (LPD) method as a buffer layer and coat TiO¬2 particles on LPD-TiO2 films by spin-coating method as anode of dye-sensitize solar cell (DSSC). In order to adjust the optical absorption edge of titanium dioxide to the visible light, we co-dope fluorine and nitrogen into TiO2 by LPD method and Ammonium Fluoride (NH4F). In our experiment, the morphology and thickness was characterized by scanning electron microscopy (SEM), structure was characterized by X-ray diffraction (XRD), chemical properties was characterized by electron spectroscope chemical analysis (ESCA), structural and spectral properties were characterized by ultraviolet-visible spectroscopy (UV-Vis) spectroscopy and current-voltage (I-V) characterization of solar cells was measured by B1500A. In our results, we enhance the performance of TiO2 as a DSSC`s anode, the open circuit voltage can reach to 0.71 V, the short circuit current can reach to 5.14 mA, the conversion efficiency can reach to 1.91 % and the fill factor can reach to 52.5 %.

Photovoltaic (PV) conversion of solar energy appears to be one of the most promising ways of meeting the increasing energy demand. In space, photovoltaic power source is the only safe alternative. Conventional silicon solar cell technologies have seen several improvements and off late GaAs/Ge and multijunction solar cells are developed to improve conversion efficiency. Demand for higher power, smaller size, lesser weight and higher efficiency has necessitated the use of high frequency switching power conditioners, which requires a better understanding of the AC characteristics of the solar cell, especially its capacitance. Solar cell is large p-n junction diode, whose AC parameters (capacitance and resistance) varies nonlinearly with its operating voltage, temperature and depend on the method (frequency or time domain) of measurement.Hence, studies on AC parameters of solar cells is taken up involving development of instrumentation, measurements on various types of solar cells and applications of AC parameters on switching shunt regulators. In the present research work a measurement set-up to measure the solar cell AC parameters using impedance spectroscopy technique is established first with the commercial instruments. Here a small AC voltage (<VT) is applied about the operating voltage (DC bias) and its complex impedance is measured from the resultant current over a wide range of frequencies. Cell capacitance, parallel resistance, series resistance and inductance are estimated from the impedance spectrum, which is plot of the cell impedance in a complex plane. The principle of measurement, details of measurement set-up with calibration, testing and limitations observed when applied to solar cells, are presented. To over come the limitations in the measurement set-up, a dedicated userfriendly instrument called Solar Cell Impedance Analyser is developed to measure solar cell AC parameters. It is a personal computer based virtual instrument, which has a power amplifier, a high-speed data acquisition card and an arbitrary function generator card with a custom built micro controller based hardware with an application specific software developed using graphical programming language. A novel concept of software range extender is introduced, which virtually increases the dynamic range of the power amplifier.

Photovoltaic (PV) conversion of solar energy appears to be one of the most promising ways of meeting the increasing future energy demand. In space, photovoltaic power source is the only alternative. The demand for higher power has necessitated the use of high speed switching charge controller and power conditioner. To design an efficient and reliable switching charge controller, the static (I-V) and dynamic (AC) characteristics of a solar cell need to be understood. The AC parameters of a solar cell can be measured either by Frequency Domain technique or by Time Domain technique. In frequency domain technique, a small signal is applied about the operating point and the AC parameters are measured. Hence, in the frequency domain technique the steady state values of AC parameters at a particular operating condition are measured. In time domain technique, a transient measurement is made where the cell voltage varies from short-circuit to open circuit or vice versa. Hence, this technique gives only the time constant of a solar cell. The impedance spectroscopy is a frequency domain technique widely used in electro chemistry to study battery characteristics. In the present investigation, the impedance spectroscopy is proposed for measuring the AC parameters of solar cells. An experimental set-up has been developed to measure the solar cell AC parameters. The AC parameters of Silicon (BSR and BSFR) solar cells and GaAs/Ge solar cells are measured using impedance spectroscopy (IS). The cell capacitance, the parallel resistance and the series resistance are measured and compared. GaAs/Ge solar cell has shown only transition Capacitance throughout its operating range while silicon (BSR and BSFR) solar cells exhibited both transition and diffusion capacitances. Theoretical and experimental values of the cell parallel resistance are compared and are in good agreement. While the diode factor in silicon solar cell varies from 2 to 1, where as in GaAs/Ge solar cell it varies from 4 to 2 to 1. Measurements conducted using open circuit voltage buildup (time domain technique) on silicon BSR solar cell shows that the collected data can be used for the restricted purpose of measuring cell transient response. The dime domain technique could not estimate the solar cell. It may be noted that the impedance spectroscopy assumes piece-wise linearity of the solar cell characteristics, lending itself for easy measurement and modeling. This assumption is valid as the signal amplitude is less than thermal voltage (VT). Since, the parameters are measured under steady state, the values are more stable and accurate. An attempt has also been made to correlate the measured AC parameters with the requirements of switching charge controllers. These correlations can be used to design the switching controllers for device rating, circuit stability and other aspects.