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A study is carried out in which synchrotron-based x-ray absorption microspectroscopy (mu-XAS) is applied to identify the chemical states of copper-rich clusters within a variety of silicon materials. The results show the effectiveness of aluminum gettering for the removal of copper from bulk silicon that is quantified via x-ray fluorescence microscopy and a segregation coefficient is determined from experimental data to be at least (1-2)*1000.

Cu([In.sub.1-x][Ga.sub.x])[Se.sub.2] (CIGS)-based thin film solar cells fabricated using transparent conducting oxide (TCO) front and back contacts were investigated. The cell performance of substrate-type CIGS devices using TCO back contacts was almost the same as that of conventional CIGS solar cells with metallic Mo back contacts when the CIGS deposition temperatures were below 500[degrees]C for Sn[O.sub.2]:F and 520[degrees]C for ITO. CIGS thin film solar cells fabricated with ITO back contacts had ah efficiency of 15.2% without anti-reflection coatings. However, the cell performance deteriorated at deposition temperatures above 520[degrees]C. This is attributed to the increased resistivity of the TCO's due to the removal of fluorine from Sn[O.sub.2] or undesirable formation of a [Ga.sub.2][O.sub.3] thin layer at the CIGS/ITO interface. The formation of [Ga.sub.2][O.sub.3] was eliminated by inserting an intermediate layer such as Mo between ITO and CIGS. Furthermore, bifacial CIGS thin film solar cells were demonstrated as being one of the applications of semi-transparent CIGS devices. The cell performance of bifacial devices was improved by controlling the thickness of the CIGS absorber layer. Superstrate-type CIGS thin film solar cells with ah efficiency of 12.8% were fabricated using a ZnO:Al front contact. Key techniques include the use of a graded band gap Cu[(In,Ga).sub.3][Se.sub.5] phase absorber layer and a ZnO buffer layer along with the inclusion of [Na.sub.2]S during CIGS deposition. Keywords: Cu(In,Ga)[Se.sub.2]; Bifacial solar cells; Transparent conducting oxides; Superstrate solar cells

A study was conducted to examine the influence of three different fullerene derivatives on the charge generation and recombination dynamics of polymer/fullerene bulk heterojunction (BHJ) solar cell blends. The internal electric field in combination with polarization effects and the dynamic nature of polarons in the BHJ solar sell are the key features to overcome electron-hole interaction to form free extractable charges.

The rear contact formation of the passivated emitter and rear cell device structure is studied. The analysis has application in Al-Si processes and advanced solar cells concepts like back-contact and rear passivated solar cells.

Si Nanohole arrays are shown as a superior sunlight-absorbing nanostructure for photovoltaic solar cell applications. The nanohole array geometry has presented a novel and viable method for cost-efficient solar energy conversion.

A core phthalocyanine platform has allowed engineering of the solubility properties of the band gap, shifting the maximum absorption toward the end. A simple method is described for increasing the efficiency of heterojunction solar cells by using a self-organized blend of phthalocyanine chromophores prepared by solution processing.

The deposition of a stack of amorphous (a-Si:H) and microcrystalline ([mu]c-Si:H) tandem thin film silicon solar cells (micromorph) which requires at least twice the time used for a single junction a-Si:H cell is described. The asymmetric intermediate reflector presented in the study separates the growth and light scattering issues of the tandem micromorph solar cells.

A comprehensive optoelectronic device model developed for organic bulk-heterojunction solar cells is presented. The measurement analysis of the short-circuit current dependence on the active layer thickness and current-voltage curves in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester based solar cells which identified a set of parameter values including dissociation parameters that describe the experimental data is also presented.

The case of corrugated thin-film solar cells structures and the optimization of these structures are studied by considering photonics. The simulations on the typical pyramid sizes have demonstrated the optimization of the global light energy intake by using corrugations of increasing complexity.

The band structure of a two-dimensional GaAs/AlGaAs superlattice is calculated and the ultimate efficiency of solar cells is estimated by using this type of structure for solar energy conversion. The ultimate efficiency is determined versus structural parameters including the filling fraction, where the efficiency of the superlattice has exceeded the efficiency of each component material in the monolithic state in a wide range of parameter values.

The optics of microcrystalline silicon thin-film solar cells with integrated light trapping structures is examined. The effect of the grating period and the grating height on the short circuit and the quantum efficiency is examined and the enhanced quantum efficiencies are seen for the red and infrared parts of the optical spectrum.

A series of donor-acceptor (D-A) co-oligomers with oligo(fluorene-alt-bithiophene) and perylene diimide as donor and acceptor segments are designed and prepared. They can self-assembly into alternating D-A lamellar nanostructured films with the periods depending on the molecular length and these films are used in fabrication of high-performance single-molecular solar cells with power conversion efficiency up to 1.50%.

The material [alpha]-[omega]-bis-(dicyanovinylen)-sexithiophen (DCV6T) is described as donor material in organic solar cells. The solar cell using the hybrid-planar-mixed heterojunction has achieved the best combination of parameters and the mixed heterojunction solar cells have improved currents.

The performance of organic solar cells based on pentacene/[C.sub.60] heterojunctions as a function of active area is described and the degradation of the performance with increased area is analyzed in terms of the power loss density concept. The metal grids are prepared onto indium-tin-oxide (ITO) and passivated with an insulator to prevent electrical shorts during the deposition of the top Al electrode and the series resistance is reduced to improve the performance by integrating metal grids onto ITO.

Photocurrent transients in all-polymer bulk-heterojunction solar cells based on poly(3-hexylthiophene) and poly(9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2',2'-diyl) are studied. The transient photocurrent features are reproduced by using a time-dependent drift-diffusion model by incorporating the trapping and detrapping of electrons.

The polycrystalline silicon (pc-Si) layers with variable grain sizes were constructed by changing the crystallization temperature of the AIC process and determine if larger grains resulted in better solar cells. The crucial impact of seed layer on the intragrain defect formation for the pc-Si layers based on AIC and epitaxial growth suggested that in addition to increased grain size, the intragrain quality of the material should also be considered in order to improve material quality and achieve high device performance.

Laser irradiation at 157 nm was used to chemically modify thin films of ethyl polyhedral oligomeric silsesquioxane (ethyl-POSS) containing polymers at different composition. The chemically modified layers which act as a shield against photodissociation and degradation of the deeper portion of the POSS polymer by VUV radiation could find applicaiton as the protection of solar cells on low orbit satellites from solar VUV photons.

The electroluminescence spectra fitted by electron hole plasma recombination model was used to observe at room temperature the band edge emission with the peak at 1.15 [mu]m from monocrystalline silicon solar cell at forward bias. The characterization of minority carrier lifetime by fitting the time evolution of radiative recombination was found to be almost constant for excess carrier density lower than 4*[10.sup.15] [cm.sup.-3] and then decreased at higher concentration.

Current-voltage (J-V) characteristics of an organic bulk heterojunction solar cell was modeled and compared with the measured characteristics of solar cell based on the blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] [C.sub.61] butyric acid methyl ester (PCBM). The results determined for the effect of the constant electric field on the charge carrier transport was utilized to solve the drift and diffusion equations to model the J-V characteristics.

The first-principles calculations combined with device simulations was used to determine the efficiency limits of solar cells made from Si[O.sub.2]/Si superlattices and from coaxial ZnO/ZnS nanowires and determine the applicability of new photovoltaic absorber materials. The studies helped to identify the critical values for mobility and lifetime that are required for efficient single junction as well as tandem solar cells.

The diode currents caused by Schotkey-Read-Hall recombination treated at the interface of pn heterojunctions to understand the activation energy of the saturation current. The results obtained serve to discriminate different cases of interface recombination and to give information about the heterojunction energy band diagram.

The application of doped hydrogenated amorphous silicon (a-Si:H) films of only a few nanometer thin for a-Si:H/crystalline silicon heterojunction solar cells is described. The phenomenon caused by Fermi energy dependent Si-H bond rupture in the a-Si:H films which results in the creation of Si dangling bonds, counteracting intentional doping of the a-Si:H matrix, and lowered passivation quality is also described.

Temperature dependent Suns-[V.sub.oc] measurements are performed on four types of polycrystalline silicon thin-film solar cells on glass substrates obtained by solid phase crystallization/epitaxy of amorphous silicon from plasma enhanced chemical vapor deposition or e-beam evaporation. The physical origin of the lowered activation energy observed for polycrystalline silicon thin-film solar cells are attributed to subgap levels acting either as minority carrier traps or shallow recombination centers.

The formation of solution-processed spherical surface textures with a monolayer of silica microspheres by convective coating, followed by a spin-on-glass film on commercial amorphous silicon solar cells is demonstrated. The improved efficiency of the omnidirectional surface texture provides an attractive solution for antireflection in both polycrystalline silicon and thin-film solar cells.

Poly(3-hexylthiophene):[6, 6]-phenyl-[C.sub.61]-butyric acid methyl ester is used as a model polymer system and different device structures are examined by using ultraviolet photoelectron spectroscopy as primary tool to investigate the reason for the S-shaped kink in the I-V curves in polymer solar cells. The anomalous feature is attributed to the presence of strong interface dipoles.

The effect of textured back reflectors on light trapping in [micro]c-Si:H cells is examined with self-orderly patterned Al substrates obtained by anodic oxidation. The optimized patterned substrate has enhanced light trapping effect in a wide range of cell thicknesses and the natural surface texturing during [micro]cSi:H film growth has improved light scattering for flat substrates, but has deteriorated the superior light scattering property of the well-designed substrates.

The features of hot carrier solar cells, from which photogenerated carriers are extracted before they are completely thermalized, are examined. A smaller effective electron mass and a higher carrier temperature are required for suppressing the heat flux to improve conversion efficiency and when the effective electron mass is much smaller than that of holes, the thermalization of holes has little impact on lowering the conversion efficiency.

Two dyes with only a two-atom change in the structure of the dye-sensitized solar cells (DSSCs) are studied. The structure of the dyes and the values for iodine binding of similar compounds have shown that the change in [V.sub.oc] is because of the difference in iodine binding at the site of the two-atom change.

The study has helped in understanding the role of hydrogen and ion bombardment during the plasma deposition as well as the effect of an epitaxial layer. The results have shown that hydrogen has played a major role in preparing high efficiency heterojunction solar cells and also the effects of the [H.sub.2] plasma has depended on the resistivity of the c-Si wafer.

The morphology of the metal multilayer films consisting of aluminum and silver in different combinations serving as semitransparent top contacts for organic solar cells is described. Multilayer metal contacts are used for preparing top-illuminated small-molecule organic solar cells (SM-OSCs) reaching efficiencies comparable to conventional SM-OSCs that use tin-doped indium oxide as electrode.

The studies have shown that the damage to the solar cell during the sputtering process is caused by a reverse bias applied to the n-i-p junctions. This reverse bias is related to the characteristics of plasma discharge and the damage mechanism might affect the solar cell process.

The finite element method and the transfer matrix method are used for performing the optical simulations of the folded tandem solar cells and four types of stacked tandem cells in order to assess their performance at upper limits. The findings showed that the folded cells are comparable to stacked tandem cells in terms of currents and power conversion efficiencies.

A study related to p-type Czochralski-grown Si ingot that is grown by using 10% solar grade silicon (SoG-Si) is presented. The results showed that the impurities could be mostly gettered by a P-diffusion step and hence are not harmful for the finished solar cell.

A study is conducted to examine the influence of the substrate surface morphology on the performance of microcrystalline silicon solar cells in the substrate or n-i-p (nip) configuration. The results demonstrated that the gain in efficiency is linked with the diminution of cracks density in the growth of the [mu]c-Si:H material and the efficiency of thin microcrystalline cells could be improved by suitable substrate and processing.

Scanning Kelvin probe force microscopy (SKPFM) method is used to perform two-dimensional study of the p-n junction in multicrystalline silicon solar cells. The results from the two-dimensional electric-field images showed that the shape of the junction follows the surface topography of the device.

A model is described for charge separation in bulk heterojunction solar cells that has combined exciton transport to the interface between donor and acceptor phases with the dissociation of the bound electron/hole pair. The effect of mobilities of the free excitons as well as the mobilities of the free charge carriers on the performance of bulk heterojunction solar cells is examined.

The synthesis of a high molar extinction coefficient organic sensitizer for high performance dye-sensitized solar cells (DSC) is described. The studies have proved that enhancing the optical absorption length of stained mesoscopic Ti[O.sub.2] film is a feasible strategy to realize a high efficiency DSC with a solvent-free ionic liquid electrolyte.

An emissivity correction method is described for lock-in thermography measurements on industrial silicon solar cells that are correctly implemented into the calibration procedure. This procedure has improved the informative value of lock-in thermography images and the reliability of the results drawn from these images.

The first approach to find the effects of lattice strain on the optical and structural properties of polycrystalline CuIn[S.sub.2] solar cell material is presented.

Hydrogenated microcrystalline silicon thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under working pressure. The influence of deposition parameters on the deposition rate and the solar cell performance were comprehensively studied as well as the structural, optical and electrical properties of the resulting solar cells.

A systematic multielement study of impurities in CdS window layers by dynamic and quantitative secondary-ion-mass spectrometry (SIMS) with high depth resolution is reported. The study was carried out on CdTe/CdS solar cell structures, with the glass substrate removed.

A systematic multielement study of impurities in CdS window layers by dynamic and quantitative secondary-ion-mass spectrometry (SIMS) with high depth resolution is reported. The study was carried out on CdTe/CdS solar cell structures, with the glass substrate removed.

An efficient air-stable p-n heterojunction organic solar cell with a structure consisting of an n-type insoluble perylene pigment penetrated by a p-type-conjugated polymer, where the interfacial area for photocurrent generation increases, is reported. The solar cells are produced by infiltrating a soluble-conjugated polymer intentionally into an opening among insoluble microcrystalline perylene layer under a saturated chloroform vapor.

The study investigates the physical origin of the electron diffusion coefficient Dn and electron lifetime Tn obtained by perturbation kinetic techniques, dependent on steady-state Fermi level or on carrier concentration. However, the model suggested in ref 56 needs further studies to determine the relationship of macroscopic steady-state time constants to microscopic models