Search

Spread spectrum time domain reflectometry (SSTDR) has proven to be effective in the detection and localization of intermittent faults on live electrical wiring. The location, shape, and magnitude of the peaks from the SSTDR signal give information about the location and type of wiring fault. To locate these faults, baseline subtraction is typically used. Unfortunately, varying weather conditions alter the SSTDR signal significantly and make baseline subtraction methods unreliable. Specifically, moisture from rain changes the relative permittivity of the cable and consequently leads to a change in the velocity of propagation (VOP) of the SSTDR signal. This change of VOP stretches the SSTDR signal and therefore shifts the peaks out of place, leading to inaccurate fault localization. Figure 1 (below) shows the described stretching effect rain has on SSTDR signals.

We report on the anisotropy of the terahertz permittivity of β-Ga 2 O 3 through terahertz transmission measurements in single crystals of (010) and (-201) orientation. The electromagnetic wave propagation in this anisotropic crystal is best described with an orthogonal set of eigenmodes, i.e., polarization eigenvectors, wherein each eigenmode possess a distinct refractive index. Polarization-dependent transmission measurements were carried out to ascertain the nature of the eigenmodes and their directions with respect to the crystal axes.

Spread spectrum time domain reflectometry (SSTDR) can be used to measure complex impedances in live electrical systems by evaluating the shape and magnitude of the reflected signature. A range of capacitors or inductors can be identified, but above and below this range, they cannot be distinguished from open or short circuits. This range depends on the frequency band of the reflectometry system and characteristic impedance of the transmission line. This can be used to characterize changes in complex impedance for the purpose of fault detection in complex loads, such as PV panels and systems.

The process for growing very large CdTe grains on MZO has been explored with the CdCl2 treatment performed for 1-30 minutes for varying film thicknesses and deposition methods.. Large grain growth occurred for thick films after 15 min. at 450°C. The minority lifetime also increased according to room temperature photoluminescence. The activation of the grain growth during the CdCl2 treatment is explained using the CdTe-CdCl2 phase diagram with preferential grain growth for Te rich grain boundaries explained by the Cd-Te-Cl Ternary phase diagram

Spread spectrum time domain reflectometry (SSTDR) has previously been used for detection and location of intermittent faults on live electrical wiring. These intermittent faults can be open circuits, short circuits, or resistive changes, all of which preserve the original shape of the SSTDR correlated waveform. But things are very different when SSTDR encounters a complex impedance discontinuity such as a capacitor or inductor. In this case, the reflection is a function of frequency, changing the shape of the SSTDR signature. In this paper, we will show the SSTDR response to single capacitors and inductors. We will also explore how SSTDR responds to arrays of PV panels (which are capacitive) connected by wires. We will show both simulations and measurements. In some configurations, it is relatively easy to see faults, although algorithms are still under development. In other configurations, little change occurs, which makes it very difficult to create a system for testing for these faults.

Semiconducting TMDs are promising candidates for THz optoelectronic devices with their ultrafast carrier dynamics and large modulation depths stemming from high photo-induced carrier concentration. In this work, we exploit the ultrafast carrier recombination in photoexcited WSe2 thin films for active THz modulation. The THz absorption was modelled as a sum of a free carrier Drude term and a Lorentzian oscillator for excitonic bound carriers. Based on this, we explore a THz modulator based on a metamaterial structure capacitively coupled to a CVD grown WSe2 film. While the THz absorption upon photoexcitation is strong close to the exciton resonance, the modulation response is limited by free carriers.

Linear energy band dispersion in Dirac semimetals has been associated with strong plasmon coupling in terahertz regime. Graphene, in this regard, has been projected to play crucial role in terahertz optoelectronics due to high carrier mobility and conductivity. However, in the realm of quantum materials, a three-dimension analogue of graphene, Cd 3 As 2 , so called 3D semimetal, has been shown to have carrier mobility and fermi-velocity well exceeding that in graphene. We experimentally demonstrate synthesis of high-quality large-area Cd 3 As 2 thin-films and realization of THz plasmonic structures. The structures exhibit quality factor ~5, at frequency of ~0.7 THz, the highest reported to-date at room temperature in any semiconductor or semimetal. Our results evidence that the 3D nature of Cd 3 As 2 provides for a more robust platform for terahertz applications than what is otherwise possible in graphene.

We present spread spectrum time domain reflectometry (SSTDR) analysis for finding faults in live PV arrays. SSTDR has been applied to a combination of PV modules, and responses are recorded and analyzed for various discrete discontinuities. An internal complex circuit diagram for a PV module is presented for the better understanding of the effect of the SSTDR signal inside the PV modules. Analysis of the SSTDR results is helpful to find the exact position of faults in PV arrays.

In this work, we report the different effects of CdCl2 treatment on CdTe films deposited by thermal evaporation onto CdS and MgZnO (MZO) buffer layers. The main finding, which is relevant for understanding recent advances in CdTe device efficiency, is that few- ${\mu}$m thick CdTe films deposited on MZO can be induced to completely recrystallize forming a film consisting of grains that span the film thickness and are up to 30 $\mu$m laterally. On CdS buffer layers, the changes in microstructure with Cl treatment are much less pronounced and the final microstructure is less ideal for thin film photovoltaics. We propose a thermodynamic framework for understanding the microstructural changes during CdCl 2 treatment which can assist in understanding the wide range of behaviors observed across the many CdTe thin film solar cell fabrication procedures.

We report on properties of As doped CdTe single crystals grown from Cd solvent by the travelling heater method.The activation energy of 70 meV derived from temperaturedependent Hall effect are consistent with As Te as the dominant acceptor. Bulk minority carrier lifetimes exceeding 20 ns are observed. We observe persistent photoconductivity, a hallmark of light-induced metastable configuration changes consistent with AX behavior. Cd-rich As-doepd CdTe single crystal was used as absorbing layer in solar cell, and this device can be performed with open-circuit voltage of 900 mV. next.

The effect of Indium (In) doping on CdTe thin film solar cells was investigated. CdTe thin films were deposited using the elemental vapor transport (EVT) technique under various Cd/Te gas phase ratios and In vapor concentrations. TCO/Buffer/n-CdTe/p-ZnTe solar cells have been fabricated and characterized. Indium doping has been found to affect the device performance. Capacitance-voltage (C-V) measurements revealed that net n-type doping increased with In concentration during the EVT deposition. Spectral response (SR) measurements indicated an enhanced carrier collection at higher In concentrations. The open-circuit voltage ($\text{V}_{\mathbf {OC}}$) and fill factor (FF) of the devices was found to increase with increased n-type doping and therefore builtin voltage. To-date n-type CdTe solar cells yielded devices with $\text{V}_{\mathbf {OC}} \quad =$ 730 mV, $\text{J}_{\mathbf {SC}} \quad =$ 20 mA/cm$^{\mathbf {2}} {, \mathbf {FF}} =$textbf 62 % and efficiency near 9 %.

We discuss the optoelectronic property variation between grains and grain boundaries of CdTe polycrystalline thin films using a confocal microscopy system. Single-photon photoluminescence (PL) and time-resolved photoluminescence spectroscopy (PL) is used to map $10 \times 10 \mu \mathrm {m}^{2}$ area at the back surface of CdTe with an optical resolution of 104 nm. TRPL maps show that different grain boundaries have different near-surface lifetimes. Surprisingly, grain-boundaries with high near-surface lifetime are associated with regions of the sample that have low PL yield. This study demonstrates the potential of confocal PL and TRPL mapping to understand carrier lifetime variations in thin films.

The CdTe solar cell back contact interface gets activated by means of thermal annealing. Depending on the back contact (BC) material the annealing time can vary between 20 - 60 minutes. In this study fast contact anneal times - $< 90$ sees - are investigated using a 60 Watt dual diode 808nm laser. Two types of back contacts are used: (a) Cu-Graphite, and (b) MoN/Mo-Cu. Laser power density (LPD) and Cu concentration were varied to study their effect on device performance. Capacitance-voltage characteristics revealed a correlation between LPD and the net doping concentration in CdTe. Higher Cu concentration was found to be detrimental to the device performance, possibly due to excess Cu reaching the CdTe/CdS interface as indicated by secondary ion mass spectroscopy (SIMS) measurements. Solar cells exhibited open-circuit voltage (Voc), short-circuit current (Jsc), and fill-factor (FF) similar to the baseline thermally anneal devices. To-date the LPD was optimized with best cell parameters being: $\mathrm{V_{oc}} ={830} \ \mathrm{mV}, \ \mathrm{J_{sc}} ={22} \ \mathrm{mA/cm}^{2}$, and $\mathrm{FF}=70\%$, for laser anneal time of 90 seconds.

In this paper we study the structural properties of Cu 2 ZnSnS 4 (CZTS) synthesized by cosputtering binary sulfide followed rapid thermal annealing (RTA) as functions of temperature and composition. By annealing identical samples at different temperatures we were able to find the optimum temperature for annealing samples in our RTA furnace. With this information, we annealed samples with a variety of discrete compositions at the optimum temperature to study the compositional differences on the optical, electrical and the structural differences on CZTS thin film crystallization. Samples were evaluated by x-ray diffraction, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Sample rich in Cu tended to form areas of CU 2-x S. It was confirmed that Sn loss during annealing increases with increased annealing temperature. Samples rich in tin before annealing grew larger grains indicating that Sn can also playa role in grain growth.

Photon absorption is a critical process for photovoltaic operation, yet the effect of illumination on semiconductor growth and processing is rarely investigated. In this work we investigate the effect of illumination during the cadmium chloride (CdCl2) annealing treatment of cadmium telluride (CdTe) thin films for photovoltaic applications while keeping the sample temperature constant. Illumination at 808 nm with varying intensity (0, 0.5, 1 and 1.5 W) when incident on CdTe during thermal CdCl2 treatment of CdTe lead to enhancement of grain size and optoelectronic properties of CdTe. However photoassisted etching of the CdTe surface is also observed at illuminations sufficiently low that the sample temperature was barely affected during annealing. Additionally, annealing under high illumination sufficient to drive CdCl2 annealing in the absence of a furnace has no such effect on the CdTe surface. We attempt to reconcile these observations and provide rationale for further experiments.

Cd-rich CdTe single crystals were grown from Cd solvent in the traveling-heater method (THM) rather than the more common Te solvent used for high-resistivity CdTe. The growth process from Cd solution in terms of the solid-liquid interface shape and group- V doping under Cd-rich condition were investigated. Stable, flat solid-liquid interfaces can be obtained by optimizing THM furnace temperature profile. An apparent doping limit in the 1016 to 1017cm−3range which scales weakly with increasing group- V element concentrations in the Cd-rich CdTe samples were indicated from capacitance-voltage measurement. The two-photon excitation time-resolved photoluminescence revealed a bulk lifetime of 20–40 ns.

Larger grain sizes and crystallographic texture in the absorber layer are correlated with performance in polycrystalline inorganic thin film solar cells because they lead to reduced densities of recombination centers and traps at grain boundaries. In this work, we compare the effects of rapid thermal annealing (RTA) and furnace annealing on film morphology, grain growth, and crystallographic texture in Cu2ZnSnS4 (CZTS) thin films deposited on Mo-coated glass by RF cosputtering. Using x-ray diffraction (XRD),scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), we show that RTA induces significant grain growth and texture without the degradation of the substrate caused in furnace annealing by the high temperatures required for CZTS phase formation. CZTS grains grown in RTA annealed samples were 2–3 times larger than those in furnace-annealed samples. Significantly, this is demonstrated in RTA on sodium-free glass which implies that RTA and similar processing methods may be capable of producing desirable CZTS grain distributions on alternative substrates such as metal foil, plastic, or thin glass.

General rules to reduce models of polycrystalline photovoltaic materials such as amorphous silicon (a-Si), cadmium telluride (CdTe), and Cu(In, Ga)Se 2 (CIGS) to 1D have been sought for decades. However, a key limitation associated with the 1D simulation of thin-film photovoltaics is the absence of grain boundaries (GBs), which are commonly found in polycrystalline solar cells. Depending on the orientation of growth, GBs are categorized as columnar GBs (roughly perpendicular to incident sunlight) and horizontal GBs (perpendicular to incident sunlight). In this work, we investigate whether polycrystalline grain materials can be appropriately treated as an effective medium, using 1D and 2D simulations of CdTe solar cells that are CSS grown and Br:MeOH+CdCl 2 treated. It is found that the grain boundary interface recombination has a marked effect in degrading Voc, which is consistently difficult to capture in a 1D model of an effective medium. In particular, we show that if the initial I-V curve of polycrystalline CdTe does not exhibit a low Schottky barrier, then Br:MeOH-etching the back will not necessarily improve device performance.

We report observations of minority carrier interactions with deep levels in 6–8% efficient Cu2ZnSn(S, Se)4 (CZTSSe) devices using conventional and minority deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS). Directly observing defect interactions with minority carriers is critical to understanding the recombination impact of deep levels. In devices with Cu2ZnSn(S, Se)4 nanoparticle ink absorber layers we identify a mid-gap state capturing and emitting minority electrons. It is 590±50 meV from the conduction band mobility edge, has a concentration near 1015/cm3, and has an apparent electron capture cross section ∼10−14 cm2. We conclude that, while energetically positioned nearly-ideally to be a recombination center, these defects instead act as electron traps because of a smaller hole cross-section. In CZTSe devices produced using coevaporation, we used minority carrier DLTS on traditional samples as well as ones with transparent Ohmic back contacts. These experiments demonstrate methods for unambiguously probing minority carrier/defect interactions in solar cells in order to establish direct links between defect energy level observations and minority carrier lifetimes. Furthermore, we demonstrate the use of steady-state device simulation to aid in the interpretation of DLTS results e.g. to put bounds on the complimentary carrier cross section even in the absence its direct measurement. This combined experimental and theoretical approach establishes rigorous bounds on the impact on carrier lifetime and Voc of defects observed with DLTS as opposed to, for example, assuming that all deep states act as strong recombination centers.

Cu 2 ZnSn(S, Se) 4 (CZTSe) is an earth-abundant semiconductor with potential for economical thin-film photovoltaic devices. Short minority carrier lifetimes contribute to low open circuit voltage and efficiency. Deep level defects that may contribute to lower minority carrier lifetimes in kesterites have been theoretically predicted, however very little experimental characterization of these deep defects exists. In this work we use admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) to characterize devices built using CZTSSe absorber layers deposited via both coevaporation and solution processing. AS reveals a band of widely-distributed activation energies for traps or energy barriers for transport, especially in the solution deposited case. DLTS reveals signatures of deep majority and minority traps within both types of samples.

The CdCl 2 heat treatment (HT) is one of the most critical steps in the fabrication of high efficiency CdTe solar cells. In this study a laser based CdCl 2 treatment is presented. A high power near infrared (808 nm) diode laser was used for laser annealing (LA) CdTe cells. The effect of laser power density (LPD) and annealing time on the devices was studied using photoluminescence (PL), current-voltage and spectral response measurements. PL spectra exhibited a correlation between the LPD and the defect density in CdTe. CdS thinning and narrowing of the CdTe bandgap was observed with increasing LPD and longer anneal times. All solar cell parameters, open-circuit voltage (VOC), short-circuit current (JSC), and fill-factor (FF), improved as a result of the laser annealing compared to as-deposited cells. The LPD was optimized with best cell parameters obtained to-date being: V OC = 800 mV, J SC = 23.34 mA/cm2, and FF= 71 %.

We present a novel method for depositing crystalline cadmium telluride (CdTe) thin films from aqueous solutions. The films were deposited via a spin-coating technique by direct conversion alternating layers of Cd and Te precursor solutions. Powder x-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images of the films show crystallization and preferential orientation of the grains to the (111) following a post-deposition thermal annealing in the presence of cadmium chloride (CdCl 2 ). This result is a promising first step towards the fabrication of a CdTe-based photovoltaic device using a solution-deposited absorber layer.

We demonstrate a low cost solution based process for polycrystalline CdTe deposition followed by a fast laser annealing step. A chemical bath deposition (CBD) process using a Cd(OH) 2 and a Te precursor solution to form polycrystalline CdTe thin films via ion-exchange reaction. This is followed by a fast laser annealing process by a 248nm excimer laser to improve the grain size of the deposited CdTe layers. X-ray diffraction analysis shows that the CBD process favors the growth of (111) CdTe. Additionally the laser treatment improves the crystalline quality of the films as is evidenced by a decreased FWHM of the (111) XRD peaks of the laser treated samples.

We present an updated equivalent circuit model based in the physics of heterojunction devices and apply it in the interpretation of admittance spectroscopy from CZTSe photovoltaic devices. We investigate the effects of fundamental device parameters on capacitance-frequency profiles and show that the widely-used derivative analysis method is only accurate for secondary capacitance steps, which may not be easily distinguished from the main junction capacitance-frequency step. We investigate whether a distribution of depletion widths or other temperature dependencies in the capacitance can account for the behavior of the main capacitance step and find that only a strong temperature-dependent series resistance can explain the frequency shift of the main capacitance step. For the samples studied, this resistance appears to be non-monotonic. We discuss the validity of this result within a model of thermionic emission over a back contact having a distribution of barrier heights.

Post-deposition laser processing of CdTe has potential for reducing manufacturing costs of CdTe PV modules. In this work we demonstrate the applicability of lasers to thermally processing CdTe modules by using a continuous wave Nd:YAG 1064 nm laser to drive CdCl2 treatment of CdTe. The data show that, similar to traditional annealing, laser annealing for only 15 seconds at higher than typical temperatures, the annealed CdTe displays an increase in A-center peak (1.435 eV) in photoluminescence yield. These indicate that chlorine activation of the absorber layer occurs in a mere 15 s and demonstrates the potential of accelerating the post-deposition CdCl2 treatment of CdTe by utilizing laser annealing at higher temperatures.

We present a device physics and equivalent circuit model for admittance spectroscopy of CZTSe based photovoltaic devices. The experimental variations of the capacitance and conductance in the depletion width are reproduced for state of the art coevaporated CZTSe devices. We will show that simple Arrhenius analysis of the main capacitance step seen in CZTSe results in erroneous values for the dominant acceptor energy. We will also show that the bulk resistivity in the quasi-neutral region (QNR), even in the presence of the dominant acceptor freezeout, cannot account for the observed increase in series resistance which is responsible for the temperature dependent frequency shift of the capacitance step. Thus, we suggest that dopant freezeout must affect another component of the lumped series resistance such as a non-Ohmic back contact.

One method for producing CuInSe 2 (CISe) absorber layers is electrodeposition followed by annealing. Replacing the commonly used furnace annealing step with a laser can reduce annealing times by 2–3 orders of magnitude: from 30 minutes to 1 s. However, laser processing has, to date, not resulted in absorber layers which can form functioning final devices. One reason is due to Se loss during annealing even on these short timescales. We show how this Se loss is reduced by using a background partial pressure of Se (P Se ) during annealing. Higher P Se results in increased grain size and drastically increased photoluminescence yield. The introduction of an elevated P Se in the laser annealing chamber enabled the fabrication of the first known CuInSe 2 photovoltaic device using electrodeposition followed by laser annealing which gave 1.6% efficiency.

Pulsed UV laser treatments have recently been applied to polycrystalline CdTe solar cells to create an ohmic back contact. In this work, we investigate the surface stoichiometry variations produced by pulsed laser excitation using X-ray photoelectron spectroscopy (XPS). These results reveal surfaces that are becoming more Cd-rich, counter to what is expected from calculations and what has been measured by others. To understand this apparent disagreement, we have constructed a geometric model of the sample surface considering surface topography and a segregation of phases at the surface. From this, we infer that the laser treatments do produce a Te enrichment as expected, but that this enrichment is localized near the grain boundaries. Furthermore, the apparent Cd-enrichment occurs because the Te-rich region's contribution to the XPS intensity is lessened by topographic and surface sensitivity effects as well as a sub-monolayer of Cd found elsewhere on the film surface.

It is assumed that the performance of polycrystalline CdTe photovoltaic thin films is correlated to microstructure, especially aspects of the microstructure related to grain boundaries. However the role of grain boundaries on the electrical performance of these films is not well understood. In an effort to gain understanding into the correlation between the performance and grain boundaries in CdTe thin films, electron backscatter diffraction (EBSD) has been used to characterize the the grain size, grain boundary structure and texture of sputtered CdTe at varying deposition pressures before and after CdCl 2 treatment. Weak axisymmetric (or fiber) textures were observed in the as-deposited films. At lower deposition pressures (111) fiber textures were observed and (110) fiber textures were observed at higher lower deposition pressures. Samples treated with CdCl 2 exhibited significant grain growth with a high fraction of twin boundaries. A much stronger correlation of performance with grain size was found when the grain size was corrected to exclude the twin boundaries. This observation confirms that the twin boundaries do indeed have different electrical properties than random high-angle boundaries.

The concept of optical path length enhancement is a useful tool for characterizing the effects of light trapping in thin films by providing a convenient geometrical interpetation of energy absorption. However, path length calculations cannot distinguish between absorption gains due to better antireflection versus absorption gains due to actual scattering of incident rays. We therefore introduce a similar metric of equivalent deflection angle to describe the effective scattering of light by a textured surface. This new concept provides useful information about light trapping that path length alone cannot. The paper begins with the geometrical interpretation of the metric and then demonstrates the insights derived from light scattering by a simple textured surface.

We investigate the light-trapping effects of dielectric nanoparticles embedded within the active semiconductor layer of a thin-film solar cell. The baseline model consists of a 1.0 μm slab of crystalline silicon on an aluminum back contact topped with a 75 nm Si 3 N 4 anti-reflective coating. Using finite-difference time-domain (FDTD) simulations, we calculate the absorption gain due to a periodic array of SiO 2 nanospheres with characteristic depth, diameter, and pitch. Under optimal conditions, spectrally integrated absorption gain due to embedded spheres can reach as high as 23.4 % relative to the baseline geometry. Using a geometry with an Au-core and SiO 2 shell, it is even possible to reach 30 % after accounting for Ohmic losses. We also discuss the trade-offs between broadband scattering efficiency, poor absorption at long-wavelengths, and semiconductor displacement due to the embedded nanospheres.

Electron backscatter diffraction (EBSD) has been used to characterize the grain size, grain boundary structure, and texture of sputtered CdTe at varying deposition pressures before and after CdCl 2 treatment in order to correlate performance with film microstructure. It is known that twin boundaries may have different electrical properties than high-angle grain boundaries and in this work we have included the effects of twin boundaries. We found better correlation of solar cell device performance to the twin-corrected grain size than to the standard grain size. In addition, we have correlated the photoluminescence (PL) spectra with device performance and with the EBSD results. We find that sputtering at 18 mTorr yields the highest efficiency, largest twin-corrected grain size and the strongest PL.

In this report we investigate the effects of pulsed laser annealing (PLA) on both as-electrodeposited (ED) and electrodeposited-furnace annealed (EDA) CuInSe 2 (CIS) samples by varying the laser fluence (J/cm2) and number of pulses. Results for as-ED samples indicate that liquid CIS-phase formation during PLA with 248 nm laser is to be avoided as liquid CIS dewets on Mo [1] as well as MoSe 2 . In the case of EDA-PLA samples, scanning electron microscopy (SEM) images suggest no apparent change in surface morphology but photoluminescence (PL) indicates change in PL yield and FWHM after PLA processing, a possible indication of annealing of defect states. The effects of PLA on defects are further explored using deep level transient spectroscopy (DLTS).

III-nitrides have recently been demonstrated as potential photovoltaic device material particularly in the high-energy portion of the solar spectrum [1–2]. The large lattice mismatch between InN and GaN however, makes it difficult to grow good quality high In-composition InGaN films for low bandgap subcells. The integration of III-N based solar cells, which have currently been demonstrated to work well above 2.0 eV, with mature IV and III–V based solar cell technologies, which work well at bandgaps ≤ 2.0 eV, has the potential to improve the efficiency of current multi-junction solar cells. In this paper, we present the first on-wafer integration of InGaN/GaN solar cells with non-III-nitride (GaAs) solar cells.

Copper zinc tin sulfide (CZTS) is a promising Earth-abundant thin-film solar cell material; it has an appropriate band gap of ∼1.45 eV and a high absorption coefficient. The most efficient CZTS cells tend to be slightly Zn-rich and Cu-poor. However, growing Zn-rich CZTS films can sometimes result in phase decomposition of CZTS into ZnS and Cu 2 SnS 3 , which is generally deleterious to solar cell performance. Cubic ZnS is difficult to detect by XRD, due to a similar diffraction pattern. We hypothesize that synchrotron-based extended X-ray absorption fine structure (EXAFS), which is sensitive to local chemical environment, may be able to determine the quantity of ZnS phase in CZTS films by detecting differences in the second-nearest neighbor shell of the Zn atoms. Films of varying stoichiometries, from Zn-rich to Cu-rich (Zn-poor) were examined using the EXAFS technique. Differences in the spectra as a function of Cu/Zn ratio are detected. Linear combination analysis suggests increasing ZnS signal as the CZTS films become more Zn-rich. We demonstrate that the sensitive technique of EXAFS could be used to quantify the amount of ZnS present and provide a guide to crystal growth of highly phase pure films.

This study investigates the synthesis of chalcopyrite Cu 2 Si 1−x Sn x S 3 (CSTS) thin films for photovoltaic solar cell absorber layers. Preliminary results indicate that layered sputtering of Cu, Sn, and Si followed by annealing in a sulfur atmosphere at 500°C does not provide adequate mixing or sulfur incorporation. Annealing/sulfurizing a homogeneous co-sputtered film of Cu, Sn, and S lead to CSTS formation, although low sulfur incorporation and undesired copper sulfide phase formation resolved. Sputtering from sulfide targets may lead to formation of CSTS.