It is well known that the cadmium chloride annealing treatment is an essential step in the manufacture of efficient thin film cadmium telluride solar cells. It has been recognized that the combination of annealing at ∼4000C together with the addition of cadmium chloride at the surface induces re-crystallisation of the cadmium telluride layer and also affects the n-type cadmium sulfide. We have applied advanced micro-structural characterization techniques to distinguish the effect of the annealing and the cadmium chloride treatments on the properties of the cadmium telluride deposited via close space sublimation (CSS) and relate these observations to device performance. Transmission electron microscopy (TEM) has shown a variation in stacking fault density with annealing temperature and annealing time. Stacking faults observed within the cadmium telluride grains in TEM were partially removed post annealing; these findings show that temperature alone has a role in the reduction of stacking faults. However, since we have previously observed almost complete removal of stacking faults with annealing in combination with cadmium chloride, the cadmium chloride is essential to defect removal and high efficiency cells.

Cu(InGa)Se2 solar cells modeling is challenging due to their complex electronic structure, to the presence of interface states between layer and grains and to the microcrystalline structure of the absorber. Here we present a ISE-TCAD based realistic absorber 3D model, with the specific objective to take into account, among several effects, these challenging aspects. The CdS/Cu(InGa)Se2 solar cell is modeled as an array of columnar microcells, connected in parallel, mimicking the polycrystalline nature of the absorber. The model optical and electrical parameters are optimized based on a review of available experimental material characterization and realization results. Simulation outcomes are compared with experimental data in order to validate the model.

For CdTe there is no real distinction between defects and impurities exists when non-shallow dopants are used. These dopants act as beneficial impurities or detrimental carrier trapping centers. Unlike Si, the common assumption that the trap energy level Et is around the middle of the band-gap Ei, is not valid for thin film CdTe. Trap energy levels in CdTe band-gap can distributed with wide range of energy levels above EF. To identify the real role of traps and dopants that limit the solar cell efficiency, a series of samples were investigated in thin film n+-CdS/p-CdTe solar cell, made with evaporated Cu as a primary back contact. It is well known that process temperatures and defect distribution are highly related. This work investigates these shallow level impurities by using temperature dependent current-voltage (I-V-T) and temperature dependent capacitance-voltage (C-V-T) measurements. I-V-T and C-V-T measurements indicate that a large concentration of defects is located in the depletion region. It further suggests that while modest amounts of Cu enhance the cell performance by improving the back contact to CdTe, the high temperature (greater than ∼100°C) process condition degrade device quality and reduce the solar cell efficiency. This is possibly because of the well-established Cu diffusion from the back contact into CdTe. Hence, measurements were performed at lower temperatures (T = 150K to 350K). The observed traps are due to the thermal ionization of impurity centers located in the depletion region of p-CdTe/n+-CdS junction. For our n+-CdS/p-CdTe thin film solar cells, hole traps were observed that are verified by both the measurement techniques. These levels are identical to the observed trap levels by other characterization techniques.

In this paper, we report new phase of crystalline silicon, quasicrystalline silicon thin-film on glass substrate. The surface topography of these films reveal simultaneous existence of sixfold and fivefold symmetry. We found an array of quasi-unit cell in 2-D that formed quasicrystalline solid. This is first time demonstration of quasicrystalline for single element, silicon (Si). Raman spectra suggests that we found crystalline silicon structure on glass substrate that is not single-crystal silicon (c-Si) but very close to c-Si.

InGaN epilayers have been investigated for use in photovoltaic solar cells for the past years. At present, almost all photovoltaic device structures reported have exhibited very low short circuit currents and thus very low solar conversion efficiency. This phenomenon has been attributed to point and extended defect chemistry in InGaN epilayers (e.g. vacancies, misfit dislocations, and V-defects), as well as to spinodal decomposition of the strained InGaN wurtzite lattice system. These defects become more dominant for higher indium concentration InGaN epilayers needed for multijunction photovoltaic device structures. In this work, we will report on the growth and characterization of indium-rich InGaN epilayers that have been grown by novel MOCVD growth technology, including the growth at superatmospheric reactor pressures.

In this work, we study CdTe thin films used in CdTe/CdS solar cells with a substrate configuration, which allows for better control in forming the junction, and the possibility for using flexible non-transparent substrates. We studied the properties of CdTe films grown at 450° and 550°C, with and without a CuxTe layer, and before and after CdCl2 treatment. We analyzed the structural and electro-optical properties using electron backscatter diffraction (EBSD), cathodoluminescence (CL) and X-ray diffraction (XRD), and investigated how the film structure, stress, and defect structure changes with the different growth conditions.

High-quality (010)-oriented epitaxial β-FeSi2 films were grown on Si(110) substrates by coating silver thin layer. The full width at half maximum of the rocking curve of β-FeSi2040 was 0.14o for the film deposited at 800°C on Si(110) substrates with 95 nm-thick silver layer. Moreover, this epitaxial β-FeSi2 film was constructed with single domain structure, and the lattice parameter of a-axis was extended by 0.7%. The photoluminescence spectrum from this epitaxial β-FeSi2 indicated that the band-gap was modulated by lattice strain of a-axis.

Measurements with the CELLO (solar cell local characterization) technique in the LBIC (laser beam induced current) mode under dark conditions with various constant bias voltages are used to analyze the lateral distribution, and mean values, of photocurrent response maps. Local solar cell defects such as local shunts were found to have a characteristic bias voltage dependence: At negative and small positive voltages a local shunt resistance gives less current response than the adjacent area. Upon applying higher positive voltages, a transition of the mean value to lower current response and an inversion of the local defect characteristics are found. These results were modeled by a newly introduced three dimensional (3D) equivalent circuit model of a solar cell divided into subcells.

Measurements and simulations of solar cells with various local defects show our method to be a new powerful tool for the quantitative analysis of local solar cell defects.

Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising absorber material for photovoltaic applications. Nanoscale electrical conductivity and overall electronic quality of this material are significantly affected by film microstructure, specifically the density and dimension of grains and grain-boundaries (GB). Local charge distribution at grains and grain/GB interfaces of nc-Si:H was studied by Electrostatic Force Microscopy (EFM) in constant force mode under illumination of white LED. Bias voltage from -3V to +3V was applied on the tip. Scanning Kelvin Force (KFM) images were taken before and after illumination to study the change in surface photovoltage (SP). EFM and KFM analysis were combined with film topography to draw a correlation between surface morphology and nanoscale charge distribution in this material. After illumination, small blister like structures were observed whose size and density increase with time. Raman spectroscopy confirmed these new structures as nanocrystalline silicon. This change was assumed due to relaxation of strained Si-Si bonds as an effect of photo response. Nanocrystalline grain interiors were at lower potential and amorphous grain boundaries were at higher potential for negative bias; it was opposite for positive bias. Change in polarity in bias voltage reversed the polarity of the potential in grains and GBs indicating the dominance of negative type of defects. Further study with current sensing AFM in dark and illumination with variable bias voltages will be able to identify the type and density of defects in grains and grain/GB interfaces.

Thin-film silicon solar cells have been attracted a lot of intention as low-cost solar cells. One of the most important technologies for improving their performances is light trapping. We have demonstrated the high potential of double-textured zinc oxide (ZnO) thin films used as front transparent conductive oxide (TCO) films due to further enhancement of their light-trapping effects. Although the laser scribing method has already been well established for low-cost thin-film silicon solar cell module manufacturing, laser scribing technique on double-textured ZnO is new and still a challenging issue. In this study, we firstly demonstrated the availability of laser scribing for amorphous silicon (a-Si) solar cells fabricated on double-textured ZnO substrates. It is general to utilize lasers with wavelength of 1.06 μm and 532 nm for scribing of TCO and silicon layer, respectively. Here we attempted to scribe both of TCO and silicon layers using a 532 nm wavelength laser (green laser) for process simplifying.

In this paper we present systematic investigations on the growth of SnS van der Waals epitaxies (vdWEs) on different substrates, including crystalline and layered substrates, by molecular beam epitaxy (MBE). Experimental growth of SnS on conventional 3D substrates, such as GaAs, indicates strong interaction between the SnS layer and the substrate resulting in poor crystallinity in general. Substantial improvement in the film crystallinity can be obtained when the deposition is made on layered substrates, with saturated surface bonds, as observed in SnS films deposited on mica and crystalline substrates with a graphene buffer layer. Crystal size as large as one micron and rocking curve FWHM of 0.118° was observed despite the large lattice mismatches. This represents significant improvement over the reported value of ∼3°. Several symmetric growth orientations are observed for films grown on mica substrates. The results indicate that weak vdW interactions between the saturated bonds of the substrate surface and the SnS unit layer which is an important factor for achieving high quality epitaxy layered materials.

We report for the first time the a-Si:H/μc-Si:H/μc-Si:H triple-junction solar cells fabricated on W-textured ZnO having a very high haze value which can improve light scattering effect. For further enhancement of light confinement effects, p-type a-SiOx:H and μc-SiOx:H as wide-gap window-layers, n-type μc-SiOx:H as intermediate layers and a back reflector were employed in these solar cells too. From theoretical analysis, we have found an advantage of a-Si:H/μc-Si:H/μc-Si:H structure for an application to low-concentration photovoltaics. For the fabricated solar cells, a conversion efficiency of 8.86% at 1 sun and and 9.86% under 7.2 suns, and a total photocurrent from each subcell of 24.1 mA/cm2 were achieved although there was still a current mismatch among component subcells.

This study provides a recipe of a 2-step selenization and sulfurization method for high strain point (HSP) glass to improve the quality of Cu(In, Ga)(S, Se)2 (CIGSSe). The recipe is distinguished by slow selenization growth before sulfurization growth at the high temperature of 580 °C. We used proto-type HSP glass instead of standard soda lime glass (SLG) to tolerate this higher temperature process. The provided slow selenization recipe improved an averaged relative efficiency by 14 percent compared to a rapid selenization recipe. We confirmed the improvement of the quality of CIGSSe which was characterized by the high crystal quality, the smooth surface, the uniform depletion layer and reduced defects as measured by XRD, SEM, EBIC and Admittance spectroscopy.

The solid oxide membrane (SOM) electrolysis process has been successfully tested on a laboratory scale to produce silicon directly from silica in a cost-effective and eco-friendly way. A one-end-closed yttria-stabilized zirconia (YSZ) tube was employed to separate a molten salt containing dissolved silica from a liquid metal anode placed inside the YSZ tube. When an applied electric potential between a liquid tin cathode in the molten salt and the anode exceeds the dissociation potential of silica, oxygen ions are transported out of the molten salt through the YSZ membrane and oxidized at the anode while the silicon cations in the flux are reduced to silicon on the surface of the liquid tin cathode. A potentiodynamic scan (PDS) was performed to determine the dissociation potential of silica in the molten salt system. Electrolysis was performed at 1.05 V for 8 hours. The presence of high-purity silicon crystals on the surface of liquid tin cathode was confirmed by scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS).

The semiconductor ZnGeN2 was grown by a vapor-liquid-solid mechanism. Ordering of the Zn-Ge sublattice with growth temperature and Zn partial pressure was investigated by powder x-ray diffraction and was found to be sensitive to the growth temperature and insensitive, over the range explored, to the Zn and NH3 partial pressures. The degree of disorder on the cation sublattice was observed to correlate with the suppression of predicted Raman peaks and the emergence of phonon density-of-states features.

Multi-junction III-V solar cells are based on a triple-junction design that employs a 1eV bottom junction grown on the GaAs substrate with a GaAs middle junction and a lattice-matched InGaP top junction. There are two possible approaches implementing the triple-junction design. The first approach is to utilize lattice-matched dilute nitride materials such as InGaAsN(Sb) and the second approach is to utilize lattice-mismatched InGaAs employing a metamorphic buffer layer (MBL). Both approaches have a potential to achieve high performance triple-junction solar cells. A record efficiency of 43.5% was achieved from multi-junction solar cells using the first approach [1] and the solar cells using the second approach yielded an efficiency of 41.1% [2]. We studied carrier dynamics and defects in bulk 1eV InGaAsNSb materials and InGaAs layers with MBL grown by MOVPE for multi-junction solar cells.

Wire array solar cells benefit from enhanced coupling of light into the active area of the device, significantly decreased collection lengths due to radial charge separation and collection, and easier access to grain boundaries for passivation which may enable future deposition on non-wafer substrates. We report on an analysis of the junction operation of wire array based GaAs solar cells through temperature and light intensity dependent current-voltage analysis and compare these data to matched planar devices. We see evidence of non-ideal recombination pathways indicated by activation energies for generation-recombination that are significantly less than the band gap of GaAs. We observe voltage shifts in the wire array devices at low temperature and high light intensity that we posit can be explained by electron accumulation in the window layers of the devices.

We present electrogenerated chemiluminescence (ECL) and fluorescence lifetime mapping of MEH-PPV/PCBM thin films. The ECL results show that the oxidation peak of MEH-PPV near 0.7 V (vs. SCE) and ECL response of films shifted positively towards 1.2 V in the presence of PCBM. At the same time, the oxidation current density of MEH-PPV increases along with the decrease of ECL intensity in the presence of PCBM. The fluorescence lifetime images clearly show that the lifetime spatial heterogeneities are affected by different substrates and MEH-PPV/PCBM ratios. Meanwhile, the lifetime of MEH-PPV decreases with the increasing of film thickness. The lifetimes of MEH-PPV films on TiO2 substrate are lower than films on glass.

The open-circuit voltage of an organic solar cell is increasing with decreasing temperature and with increasing illumination intensity. These dependencies are quantitatively investigated for two types of organic solar cells, one with a flat donor-acceptor heterojunction and one with a mixed layer bulk heterojunction. Zinc-phthalocyanine and C60 are used as donor and acceptor, respectively. A qualitative difference is found for the two geometries. We find that a logarithmic illumination intensity dependence with temperature as a linear pre-factor of the logarithm, which is commonly reported and observed, is applicable for the bulk heterojunction. The flat heterojunction, in contrast, shows a constant illumination intensity pre-factor which is independent of the temperature, and the temperature can be modeled as additional linear summand.

We present normal and inverted solution processed bi-layer solar cells using cationic cyanine dyes as the electron donor and a fullerene as the electron acceptor. The cells exhibit high open circuit voltages up to 1 volt showing the optimal alignment of donor and acceptor energy levels. We demonstrate the large effect that cyanine dye counter ions can have on the energetics of the solar cells and how the S-shaped current density vs. voltage (J-V) curves can be avoided.