The purpose of the thesis is to investigate the improvement of single-crystal Si solar cell efficiency using porous Indium tin oxide (ITO)/ITO double layer antireflection(AR) coating. The resistivity, transmittance and refraction index of the porous ITO films prepared by supercritical CO2 treatment were investigated. At a 2000 psi pressure and 60¡CC, the resistivity of porous ITO films is 15 £[-cm, the average transmittance is better than 95 %, and the refraction index is 1.54. In addition, the resistivity of ITO thin films fabricated by reactive ratio-frequency magnetron sputtering is 7¡Ñ10-4 £[-cm, the average transmittance are 85 %, and the refraction index is 2.0. For the single crystal-Si solar cell with porous ITO/ITO double layer AR coating, the open circuit voltage, short circuit current, fill factor and efficiency are measured.

Since the discovery of the photovoltaic effect in bulk heterojunction devices¡Mthe considerable publications in PSCs have been reported¡OPSCs based on the concept of bulk heterojunction (BHJ) configuration where active layer comprises of a p-type donor (conjugated polymer) and a n-type acceptor (fullerene derivative) materials¡Mrepresents the most useful strategy to maximize the internal donor-acceptor interface area allowing for efficient charge separation¡OTo further enhance the power conversion efficiency from solar cells made of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester (P3HT/PCBM) ¡M a new conducting polymer with optimized band energy levels are demonstrated to be one of the key properties¡OIn this study¡MI synthesized a soluble and strongly visible-light absorbing alternating conducting polymer using Suzuki coupling polymerization method¡OThe UV-Vis absorption spectra of copolymer contains an intramolecular charge transfer (ICT) transition band¡Mwhich leads to absorption extending to near-infrared region and optical band gaps is 1.55 eV¡OThe photo-electron spectroscopy in air(PESA) measurements show that the HOMO level of the polymer is ~5.0eV which is lower than P3HT¡O

The purpose of our research is growing the coupled InGaAs quantum dots on the n-type substrate by molecular beam epitaxy in laboratory, and we choose 5,10 and 15 nanometers to be the thicknesses of GaAs spacer between the quantum dots layer. Due to the couple effect, we hope to realize the theorem of intermediate band proved by Luque and Marti. We measure the characteristic of samples by electroluminescence spectra, photoelectric current spectra, electrical absorption spectra and electro reflectance spectra in laboratory; moreover, we acquire the basic parameters of solar cell by AM1.5G for analyzing. From the basic parameters of solar cell, we know that the quantum dots can enhance the photocurrent by absorbing additional photons , however, the strain caused by quantum dots would decay the open voltage seriously, so that the efficiency always under the baseline. Each efficiency of 9-stack QDs are 4.3%(c494),5.1%(c519),5.3% (c520),and each efficiency of 9-stack Dwells are 3.9%(c524),4.2%(c525),4.7%(c526), and 10-stack QDs(5nm) is 2.9%(c514),and 12-stack QDs(10nm) is 4.48%(c538),and 12-stack QDs(15nm) is 5.89%. The break through of this paper is that the efficiency of c529¡]VOC=0.64V,JSC=11.97mA/cm2,FF=67%,£b=5.89%¡^is higher than GaAs¡]VOC =0.87 V, JSC =7.4 mA/cm2,FF=72.3%,£b=5.6%¡^,and we attribute this performance to its good quality of miniband, because the current can be enhanced a lot, and it will make up for the lose of open voltage and filling factor, so that the efficiency can be higher than GaAs baseline.

The study proposed a high efficient dye sensitize solar cell (DSSC) by embedding liquid crystal in liquid electrolyte. When liquid crystal molecules was disperse in the liquid electrolyte, the light-scattering occur due to refractive index mismatching by randomly oriented liquid crystal droplets. The light-scattering allows solar light have longer optical path length within the solar cell and therefore enhances light-trapping efficiency of N719 dye. The experiment results reveal that the DSSC with the liquid crystal concentration of 20 wt% have best electric conversion efficiency. Moreover, the study also introduces chloseteric liquid crystal to the liquid electrolyte of a DSSC and compare with nematic liquid crystal embedded DSSC. The cholesteric liquid crystal with periodic helical structure in the liquid electrolyte provides not only light-scattering but also selective reflection. Compared with nematic liquid crystal embedded DSSC, the cholesteric liquid crystal embeded DSSC has a more large light-trapping efficiency due to combined effects of light scattering and selective reflection. Besides, when the reflective band (480~580nm) of cholesteric liquid crystal is matched to the absorption spectrum of N719 dye, the DSSC has better photoexcitation of dye and photovoltaic performance.

Alternative energy sources such as solar energy have attracted an extensive interest in the petroleum shortage era. Among solar cells, dye-sensitized solar cell (DSSC) attracts the attention of widespread research teams because of the easy-production process, low cost, and good photon-to-electron conversion efficiency. In this study, both UV and acid solution such as HCl are used to improve the efficiency of DSSC. The UV illumination can eliminate organic contaminates on TiO2 by photocatalysis and enhance the adsorption of dye molecules. Meanwhile, the coordination mode between TiO2 and dye could be changed and lower the electron transportation. If the HCl solution is used after UV illumination, the coordination mode can be preserved. Moreover, H+ from HCl can attract the COO¡Ð anchoring group of dye by electrostatic force. It further increases the adsorption of dye and improves the DSSC efficiency. The coordination mode was measured by Fourier-transform infrared spectrometer (FTIR). The internal resistance was measured by electrical impedance spectroscopy (EIS). The chemical properties were characterized by X-ray photoelectron spectroscopy (XPS). The light absorbance was measured by ultraviolet-visible spectroscopy (UV-Vis). The morphology was observed by field emission scanning electron microscope (FE-SEM). The performance of the cells was measured by a semiconductor device analyzer. In our results, the conversion efficiency was improved from 6.29% of untreated one to 6.71 and 7.39% for UV and UV + HCl treated ones.

In this thesis, we have reported the MBE growth, design, and fabrication of the InGaAs quantum dots (QDs) laser/semiconductor optical amplifier, broadband QDs structure, coupled double cavity structure for terahertz emission on GaAs substrate. The emission wavelengths of the strain-induced S-K growth mode QDs structures are adjusted through the composition of QDs and strain-compensated capping layer. Also, the technique of growing high quality InGaAs QDs with solid source molecular beam epitaxy has been established and characterized by double crystal X-ray diffraction, transmission electron microscopy, photoluminescence, electroluminescence measurements. For 1.3£gm QDs laser samples, ridge waveguide lasers of the Fabry-Perot (FP) type are fabricated by wet-etching process. From the QDs laser L-I curve, the e2-hh2 transition at £f =1160nm have larger optical gain than e1-hh1 transition at £f =1220nm. The FP laser with 0.6£gm cavity length shows a lasing peak of 1160nm at threshold. As the cavity length increase to 2£gm, the lasing peak red shift to 1220nm (closed to ground state emission wavelength). This energy band gap transition phenomenon is obvious especially in the QDs laser with quantum well (QW) structure. When the injection current increase, two lasing peaks at £f= 1160 and 1175nm are observed sequentially. This unique lasing behavior is shown to be consistent with carriers localized in noninteracting dots. For the application of 1.3£gm light source, we optimum the growth condition for different needs in optical coherent tomography (OCT) light source, tandem solar cell, terahertz emission light source, etc. For the super luminescence diode (SLED) in OCT, we design multi-stacked asymmetric QDs structure (AMQD), QDs in the well structure (DWell), Dwell with p-doping in well structure to investigate the carrier recombination condition and bandwidth. Comparing with 5 structures in this study, the Dwell with p-doping in well structure has a maximum EL bandwidth exceed 198nm. The large bandwidth is attributed to the QW which increases the carrier capture rate and the p-doping which provide the efficient holes in valance band. This structure provides an excellent SLED light source solution to replace the existing program. For the tandem solar cell, we use the multi-stack QDs to compose broadband absorption in 1eV range. In order to avoid the degradation in the open circuit voltage, we use InGaAs QW to reduce the QDs strain. We observed the doping effect on the built in field through the photo-reflectance measurements. For the better photocurrent collection, we use p-doping in the QW to increase the built-in field intensity to obtain higher efficiency. For the terahertz emission, the QDs embedded in coupled double-cavity structures with an AlAs/GaAs intermediate distributed Bragg reflector (DBR) are grown on GaAs substrates. Two emission peaks at 1180, 1206 nm from the QDs corresponding to the coupled double-cavity resonant modes are observed in the high reflection band. The frequency differences for the two resonant coupled modes are of 5.5 terahertz, and have been successfully controlled by changing the pair numbers for the intermediate DBR. In addition, we have grown the InGa(Al)As nanostructures on InP substrate. The lattice constant difference between InGaAs and InP is relatively smaller compare with GaAs substrate, and it will be more challenge in epitaxial growth. After we investigate the strain, surface morphologies, optical properties for the nanostructures, we find the group III elements play an important role in the morphologies. Wire formation is attributed by the enhanced adatom diffusion length in the stepped surface front along [0-11] direction for the presence of Ga both in the nanostructure and buffer layer. Finally, we established QDs, Qwires database for the valuable new possibilities for designing new and original structures.

We deposited CuInSe2 or CuIn1-xGaxSe2 on the substrate of bi-layer Mo by electrodeposition. Besides, we deposited bi-layer Mo by RF sputtering on soda-lime glass. First, we discussed the characteristic of Mo metal, and how can we have a good adhesion and a low resistivity simultaneously. Then, we deposited CuInSe2 and CuIn1-xGaxSe2 thin film by electrodeposition, and discussed the effect of depositing time, pH value in depositing solution, depositing current and different concentration ions respectively.

The purpose of the thesis is enhancing efficiency of asymmetric quantum dots (AMQD) solar cells. The AMQD structures are grown on the n-type GaAs substrate by (MBE). In order to enhance the photovoltaic characteristics, we introduce InGaAs quantum well (QW) and modulation doping in the well to investigate effect of the strain relief and built-in electric field in the active layer. In our experiment, we analyze the optical property of AMQD structures by photoluminescence measurement system, and then decompose emission wavelength by Gaussian fitting to find optical characteristics of each single layer quantum dots. Besides, we also measure photocurrent spectra, external quantum efficiency, electrical absorption, and electro reflectance spectra to discuss carrier transition inside AMQD structure . Finally, we acquire the photovoltaic basic parameter under one sun. The results show that QDs provide additional photocurrent via absorbing extra photons, but the open circuit voltage decrease seriously due to the accumulated strains. So as to relieve the strains and enhance carriers extraction, we introduce QW layers with different growth temperatures and change the modulation doping concentrations . From the results, the higher growth temperature for QW diminishes accumulated strains, and the higher p-type modulation doping concentration indicates an extraction enhancement due to the stronger built-in electric field. By optimizing QW growth conditions, the efficiency has overtaken GaAs baseline cells. In addition, we improve the photon-excited current collection by using matrix pattern and wet etching on the device surface, the best photovoltaic characteristic shows V OC = 0.74 V, J SC = 18.82 mA/cm2, FF = 0.78, £b= 10.86%.

This thesis studied on the research of how conducting polymer polyaniline can be used in the buffer layer of organic solar cell. There are two methods used.¡]1¡^Using spin-coating to make film of polyaniline solution.¡]2¡^Polymerizing aniline on the substrate directly by electrochemical polymerization. The electrochemical method is separated into cyclic voltammetry and potentiostatic method respectively. The latter method which improved the disadvantage of infractable thick film and low electric conductivity of polyaniline for spin-coating is chosen as the preparation method for polyaniline films. We discuss of the photoelectric characteristics and surface morphologies of polyaniline film and to make a solar cell base on Poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester measured with AM 1.5G 100 mW/cm2 solar light simulation. This research combine above-mentioned results to use potentiostatic method to polymerize polyaniline on the PEDOT¡GPSS into a compound electrode and to replace currently popular ITO positive pole in a organic solar component. The structure is PEDOT¡GPSS/PANI/P3HT¡GPCBM/Al. By electroplating polyaniline, it can enhance the electric conductivity of the film of PEDOT¡GPSS from 1 S/cm to 154 S/cm, furthermore, to reach 1.06% of photoelectric conversion efficiency and creates a new possibility of preparing a flexible organic solar cell.

The aim of this study was to modify the platinum particle size to observe the effects on the efficiency of a Dye Sensitized Solar Cell (DSCC). DSSC was prepared as follows: On the anode side, TiO2 was annealed on the transparent conducting oxide (TCO) which is SnO2:F coated and a cis-bis (isothiocyanato) bis (2,2&#039 / -bipyridyl-4,4&#039 / -dicarboxylato)&ndash / ruthenium(II) dye was adsorbed on the TiO2. On the cathode side, platinum was coated on TCO from an alcohol based solution of platinum (plasitol) by thermal decomposition method. Potassium iodide and iodine were dissolved in ethylene glycol to prepare the electrolyte. Four cathode surfaces were prepared by thermal decomposition method at 400 oC and 5 min. Cathode surface morphology was changed by changing the annealing conditions. Current-voltage measurements were performed for determining the cell efficiency. One cathode glass was used as such giving a cell efficiency of 2.36%. Three glasses were further thermally treated at 450 oC, 500 oC and 550 oC for 30 min. highest efficiency was measured with the counter electrode annealed at 550 oC for 30 min as 2.89%. SEM micrographs of the substrate which was SnO2:F coated TCO revealed a decrease in average surface particle size with an increase in annealing temperature. EDX mappings showed that as the annealing temperature increased, Pt particles segregated together to form porous patches. In this study, it was demonstrated that as the annealing temperature of cathode increased, DSSC efficiency increased. These results can be used to design cheaper DSSCs with higher efficiencies.