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In this study, substochiometric hole-selective molybdenum oxide (MoOx) contacts in crystalline silicon (c-Si) solar cells were investigated by a combination of transmission electron microscopy (TEM) and spatially resolved electron energy-loss spectroscopy (SR-EELS). It was observed that a ≈ 4 nm SiOx interlayer grows at the MoOx/c-Si interface during the evaporation of MoOx over a c-Si substrate. SR-EELS analyses revealed the presence of a 1.5 nm diffused MoOx/indium tin oxide (ITO) interface in both as-deposited and annealed samples. Moreover, the presence of a 1 nm thin layer with a lower oxidation state of Mo was detected at the SiOx/MoOx interface in an as-deposited state, which disappears upon annealing. Overall, it was evident that no hole-blocking interlayer is formed at the MoOx/ITO interface during annealing and homogenization of the MoOx layer takes place during the annealing process. Furthermore, device simulations revealed that efficient hole collection is dependent on MoOx work function and that reduction in the work function of MoOx results in loss of band bending and negatively impacts hole selectivity.

We report ultra-high responsivity of epitaxial [Formula: see text] (TGO) Schottky UV-C photodetectors and experimentally identified the source of gain as deep-level defects, supported by first principles calculations. Epitaxial TGO films were grown by plasma-assisted molecular beam epitaxy on (−201) oriented n-type β-[Formula: see text] substrates. Fabricated vertical Schottky devices exhibited peak responsivities as high as 3.5 [Formula: see text] A/W at −5 V applied bias under 250 nm illumination with sharp cutoff shorter than 280 nm and fast rise/fall time in milliseconds order. Hyperspectral imaging cathodoluminescence (CL) spectra were examined to find the mid-bandgap defects, the source of this high gain. Irrespective of different tin mole fractions, the TGO epilayer exhibited extra CL peaks at the green band (∼2.20 eV) not seen in β-[Formula: see text] along with enhancement of the blue emission-band (∼2.64 eV) and suppression of the UV emission-band. Based on hybrid functional calculations of the optical emission expected for defects involving Sn in β-[Formula: see text], VGa–Sn complexes are proposed as potential defect origins of the observed green and blue emission-bands. Such complexes behave as acceptors that can efficiently trap photogenerated holes and are predicted to be predominantly responsible for the ultra-high photoconductive gain in the Sn-alloyed [Formula: see text] devices by means of thermionic emission and electron tunneling. Regenerating the VGa–Sn defect complexes by optimizing the growth techniques, we have demonstrated a planar Schottky UV-C photodetector of the highest peak responsivity.

We experimentally proved an effective use of UV-ozone oxide layer in junction passivation and current tunneling applications of crystalline silicon (c-Si) solar cells. The UV-ozone generated oxide layer can improve the passivation quality of aluminum oxide(AlO x ) when inserted between the silicon wafer surface and atomic layer deposited(ALD) AlO x . When tested on junctions that moderately diffused by phosphorus and boron (sheet resistance R sh ~110 Ω/□), the UV-ozone oxide and AlO x stack resulted in a J 0 no more than 12fA/cm2. The same oxide layer is also considered as a passivating contact material. When applied as an interlayer between diffused silicon surface and aluminum contact, the passivated contact structure realized a contact resistivity (ρ c ) of ~ 1mΩ-cm2 and ~ 25mΩ-cm2 for boron and phosphorus passivating contact structures, respectively, with moderately doped diffusions.

We demonstrate a high figure-of-merit UV–C solar-blind photodetectors fabricated from polycrystalline beta-gallium oxide (β-Ga2O3) grown on n-Si substrates by plasma assisted molecular beam epitaxy (PAMBE). We developed film growth sequences for nucleation of Ga2O3 on (100) and (111) oriented Si substrates, and systematically investigate the influence of crucial growth parameters, namely substrate temperature, oxygen flow rate and plasma power on the functional properties of the photodetectors. The photodetectors show ultra-high responsivity of 837 A/W and fast ON/OFF time below 4ms observed under 248 nm illumination at –5V. In addition, they display strong rectifying properties and sharp cut-off below 280 nm with average responsivities between 10-80 A/W, detectivity on the order of 1010 Jones, and rise/fall times between 4 to 500 ms at –5V. High photoconductive gain is shown to likely be due to the mid-bandgap donor/acceptor defect levels, including oxygen vacancies in the form of self-trapped holes. We demonstrate that these defect levels can be modified by controlling the growth conditions, thereby, allowing for tailoring of the photodetector characteristics for specific applications. Our methodology represents a cost-effective solution over homoepitaxial approaches, with characteristics that meet or exceed those reported previously, offering new possibilities for on-wafer integration with Si electronics.

An image-processing method combined with Fourier analysis is introduced in this work as a rapid and highly-automated method of detecting rear contact voids in passivated emitter and rear contact cells (PERC). This approach utilizes photoluminescence (PL) imaging to locate the central point of the most detrimental type of voids and associate a void fraction to each cell in a manner of seconds. Acoustic microscopy and scanning electron microscopy are also used as complementary tools to confirm the presence of voids detection using PL imaging and provide more insight into the actual physical mechanism of what is observed in PL measurements.

Heterogeneous integration of β-(Sn xGa1− x)2O3 (TGO) UV-C photodetectors on silicon substrates by molecular beam epitaxy is demonstrated. Multimodal electron microscopy and spectroscopy techniques reveal a direct correlation between structural, compositional, and optical properties of TGO and the functional properties of the photodetectors. Wavelength dispersive x-ray spectroscopy results accurately determine Sn concentrations ( x) in the region of 0.020, and room temperature cathodoluminescence (CL) hyperspectral imaging shows changes in the CL emission intensity in TGO compared with a Ga2O3 sample with no Sn. Alloying Ga2O3 with Sn is shown to quench the red emission and enhance the blue emission. The increase in blue emission corresponds to the rise in VGa-related deep acceptors responsible for the high gain observed in the TGO detectors. A Ga2O3 nucleation layer is shown to improve the TGO surface quality and give better device properties compared to TGO grown directly onto the Si substrate, including a higher specific detectivity on the order of 1012 Jones.

An alternative method to image essential variables like dark saturation current density, series resistance, and cell efficiency is introduced in this work. This approach combines the terminally connected diode model with a modified technique for extracting the spatially resolved ideality factor of the cell under non-open-circuit conditions. Following a description of the steps governing the principles of this parameter imaging approach, we explore potential benefits of this technique and how it may improve upon existing methods.

This paper reports an effective and industrially relevant passivation and antireflection film stack featuring a 10 nm silicon dioxide (SiO2) film followed by a ≍65 nm amorphous titanium oxide (a-TiO x ) film. This film stack has equivalent optical performance to a single-layer silicon nitride (SiN x ) antireflection coating (ARC) for unencapsulated cells, and slightly better performance for encapsulated cells (≍0.2 mA⋅cm–2 increase). The field effect passivation properties of the SiO2/a-TiO x film stack have been modified extrinsically after the film deposition to demonstrate surface recombination velocities below 1.2 cm/s in a $\text{1}\;{\rm{\Omega }} \cdot {\text{cm}}$ n-type silicon wafer. Finally, the TiO x films have been deposited using an inline atmospheric pressure chemical vapor deposition (APCVD) system at temperatures below 350 °C, thus demonstrating this film stack offers both better passivation and optical performance, as well as a potentially lower manufacturing cost compared to SiN x , due to the use of APCVD rather than plasma-enhanced chemical vapor deposition. Simulations indicate further gains in terms of optical performance (≍0.3 mA⋅cm–2 increase compared to SiN x —encapsulated case) may be possible using a double-layer ARC featuring a polycrystalline TiO x film followed by an aluminum oxide (AlO x ). However, potential contamination from the APCVD may pose a risk to maintaining high bulk carrier lifetimes.

We report on the growth of epitaxial β–Ga 2 O 3 thin films on c-plane sapphire substrates using a close coupled showerhead MOCVD reactor. Ga(DPM) 3 (DPM = dipivaloylmethanate), triethylgallium (TEGa) and trimethylgallium (TMGa) metal organic (MO) precursors were used as Ga sources and molecular oxygen was used for oxidation. Films grown from each of the Ga sources had high growth rates, with up to 10 μm/hr achieved using a TMGa precursor at a substrate temperature of 900 °C. As confirmed by X-ray diffraction, the films grown from each of the Ga sources were the monoclinic ( 2 ¯ 0 1) oriented β–Ga 2 O 3 phase. The optical bandgap of the films was also estimated to be ∼4.9 eV. The fast growth rate of β–Ga 2 O 3 thin films obtained using various Ga-precursors has been achieved due to the close couple showerhead design of the MOCVD reactor as well as the separate injection of oxygen and MO precursors, preventing the premature oxidation of the MO sources. These results suggest a pathway to overcoming the long-standing challenge of realizing fast growth rates for Ga 2 O 3 using the MOCVD method.

In this study, the cross-section of electron-selective titanium oxide (TiO2) contacts for n-type crystalline silicon solar cells were investigated by transmission electron microscopy. It was revealed that the excellent cell efficiency of 21.6% obtained on n-type cells, featuring SiO2/TiO2/Al rear contacts and after forming gas annealing (FGA) at 350°C, is due to strong surface passivation of SiO2/TiO2 stack as well as low contact resistivity at the Si/SiO2/TiO2 heterojunction. This can be attributed to the transformation of amorphous TiO2 to a conducting TiO2−x phase. Conversely, the low efficiency (9.8%) obtained on cells featuring an a-Si:H/TiO2/Al rear contact is due to severe degradation of passivation of the a-Si:H upon FGA.

The use of proper surface preparation and cleaning methods for Si wafers prior to the deposition of passivation layers is essential to minimize surface recombination and realize high efficiencies (> 20%) in crystalline Si photovoltaic cells. In this work, the influence of wafer cleaning on the quality of surface passivation achievable for boron-doped emitters was investigated, including the use of different combinations of HCl, HF, HNO3, and ozonated deionized water (DIO3). These different surface preparations and cleaning sequences were performed on undiffused and boron diffused n-type Cz Si wafers, followed by the deposition of either silicon nitride (SiNx) or an aluminum oxide film capped with SiNx (Al2O3/SiNx stack). Additionally, both planar and anisotropically textured wafers were used. Injection-level dependent photoconductance measurements and calibrated photoluminescence imaging were performed on symmetrical boron diffused samples based on the different cleaning processes and passivation materials described above. Additionally, non-contact corona-Kelvin measurements were used to extract the total charge and interface defect density at the Si surfaces. We found that cleaning variations strongly influence carrier lifetime for SiNx passivated Si, but the effect is less pronounced in the case of Al2O3/SiNx stacks. It was further observed that DIO3-last treatment resulted in higher lifetimes for the SiNx stacks. Overall, it emerged that the (DIO3 + HF + HCl → HF → DIO3) clean is a promising and potentially low cost cleaning sequence for the photovoltaics industry.

The transmission line method (TLM) is often used in characterizing the contact resistance of c-Si solar cells by cutting cells into strips parallel to the busbars. When applying this method to industrial solar cells, we found various problems that have not been sufficiently explained in prior work. In this paper, we investigate different factors that influence the accuracy of this measurement, using both simulation and experimental methods. The following factors are shown to influence the extracted contact resistivity and are investigated in this work: (1) strip width; (2) edge shunting; (3) current flow through the intermediate unprobed fingers; (4) non-uniform contact resistance; and (5) non-uniform sheet resistance. In cases where the contact resistivity values determined from the TLM measurements and simulations were found to be inaccurate, we introduce correction procedures and measurement guidelines that reduce error. For example, when strip width is a factor, the measurement error of a 30 mm sample is reduced from 95.5% to 4.5% using a correction procedure validated by simulation. Furthermore, the methods are also shown to be very effective when applied to industrial solar cells. TLM measurements have an important role to play in both cell R&D and factory quality control, and this work can serve as a guide towards more accurate contact resistivity measurements.

The development of ultrafast quantum efficiency measurements has made it possible to perform spatially resolved short-circuit current mapping on large area crystalline silicon solar cells. With the inclusion of concurrent diffuse reflectance measurements, detailed loss analysis is presented that identifies the impact and spatial nonuniformity of various current loss mechanisms. We measure p-type multicrystalline aluminum back surface field and p-type monocrystalline passivated emitter and rear cells, and investigate details of the spatial variation in specific device layers such as the antireflection coating, phosphorus diffused region, bulk, and rear surface. The results are compared with traditional photoluminescence imaging, and are found to provide a complementary dataset that provides a comprehensive picture of device performance. The insight provided from these techniques is intended to allow rapid feedback for quality control in manufacturing and accelerate the pace of process development in research environment.

The focus of this work is on the characterization of passivated crystalline Si (c-Si) surfaces subjected to various cleaning sequences involving UV ozone (UVo) treatment and HF-dip. A combination of photoconductance decay (PCD) measurements and high-resolution transmission electron microscopy (HRTEM) studies were used to obtain a deeper insight into passivation mechanisms of UVo and its origin at the nano-scale.

Metal-semiconductor-metal (MSM) structured solar blind photodetectors were fabricated based on various Mg content wurtzite Mg x Zn 1−x O epitaxial films grown via pulsed metal organic chemical vapor deposition. The response spectra of the devices showed a peak position that shifts from ∼383 nm to 276 nm for Mg content, x , between 0.0 and 0.51, covering a wide portion of the ultra-violet spectral region, extending well into the solar blind window. At 10 V bias, a large responsivity of ∼1.8 × 10 4 A/W was obtained at 276 nm for a device based on a high Mg content (x = 0.51) MgZnO film. To the best of our knowledge, this responsivity is the highest ever reported for a MgZnO based device and its origin is attributed to large internal gain resulting from carrier trapping at the MgZnO/Ni/Au interface. This is confirmed by the presence of an asymmetric Schottky barrier height on the two MSM contacts. Conversely, the response speed of the devices was slow with the 10%–90% rise and fall times measured to be in the millisecond range. The results reported in this work show the realization of high responsivity MgZnO based solar blind photodetectors, providing a significant step in the development of MgZnO alloy based of detector.

Diamond wires from several manufacturers were investigated in term of their impact on wafer quality and cell performance. It was identified that under identical ingot sawing conditions the diamond wire make had an impact on the resulting cell performance. Several cells exhibited defects that remained with the cell even after the saw damage etching process. These defects were investigated in terms of there impact on various solar cell performance parameters. This analysis was performed using photoluminescence imaging and spatially resolved quantum efficiency and reflectance measurements. The diamond wire marks were observed to have the largest impact on the local short-circuit current density across the cell.

This article is the first in a three-part series of manufacturing metrology for c-Si photovoltaic (PV) module reliability and durability. Here in Part 1 we focus on the three primary process steps for making silicon substrates for PV cells: (1) feedstock production; (2) ingot and brick production; and (3) wafer production. Each of these steps can affect the final reliability/durability of PV modules in the field with manufacturing metrology potentially playing a significant role. This article provides a comprehensive overview of historical and current processes in each of these three steps, followed by a discussion of associated reliability challenges and metrology strategies that can be employed for increased reliability and durability in resultant modules. Gaps in the current state of understanding in connective metrology data during processing to reliability/durability in the field are then identified along with suggested improvements that should be considered by the PV community.

This article is the second article in a three-part series dedicated to reviewing each process step in crystalline silicon (c-Si) photovoltaic (PV) module manufacturing process: feedstock and wafering, cell fabrication, and module manufacturing. The goal of these papers is to identify relevant metrology techniques that can be utilized to improve the quality and durability of the final product. The focus of this article is on the cell fabrication process. In this review, the fabrication of c-Si PV cells is divided into four steps: (1) wet chemical processes; (2) emitter formation; (3) anti-reflection coating (ARC) and passivation deposition; and (4) metallization. Each of these processing steps can impact the final reliability and durability of PV modules deployed in the field, and here the failure modes and degradation mechanisms induced during cell manufacturing are explored. Additionally, a literature review of relevant measurement techniques aimed at reducing or eliminating the probability of such failures occurring is presented along with an assessment of potential gaps wherein the PV community could benefit from new research and demonstration efforts.

Thin TiO2 films are demonstrated to be an excellent electron-selective contact for crystalline silicon solar cells. An efficiency of 21.6% is achieved for crystalline silicon solar cells featuring a full-area TiO2 -based electron-selective contact.

We report on the growth of high Mg content, high quality, wurtzite Mg x Zn 1− x O (MgZnO) epitaxial films using a pulsed metal organic chemical vapor deposition (PMOCVD) method. Series of MgZnO films with variable Mg concentration were deposited on bare and AlN coated sapphire substrates. The band gap of the films estimated using UV–visible transmission spectra ranges from 3.24 eV to 4.49 eV, corresponding to fraction of Mg between x =0.0 and x =0.51, as determined by Rutherford backscattering spectroscopy. The cathodoluminescence (CL) measurement has shown a blue-shift in the peak position of MgZnO with an increasing Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The crystal structure and phase purity of the films were also confirmed by XRD analysis. Hall effect measurement in van der Pauw configuration was employed to evaluate the electrical properties of the films. With a rise in Mg incorporation into the ZnO lattice, the films became very resistive, consistent with the widening of the band gap. The AFM measurement on the films has shown a decreasing surface roughness with an Mg content. To the best of our knowledge, the current result shows the highest Mg content ( x =0.51), high quality, wurtzite MgZnO epitaxial film ever grown by MOCVD. The high Mg incorporation without phase separation is believed to be due to the non-equilibrium behavior of the PMOCVD in which the kinetic processes dominate the thermodynamic one.

Pulsed metal organic chemical vapor deposition (PMOCVD) was used to grow high Mg content, high quality, wurtzite Mg x Zn 1-x O (MgZnO) epitaxial film to realize photodetectors and emitters in the solar blind spectral window. MgZnO films with various Mg contents were deposited on c-plane Al 2 O 3 with and without AlN buffer layer. The band gap of the films range from 3.24 eV to 4.49 eV, corresponding to fraction of Mg between x =0.0 to x =0.51, as determined by Rutherford backscattering spectroscopy (RBS). Cathodoluminescence (CL) measurement showed a linear blue shift in the spectral peak position of Mg x Zn 1-x O with an increase in x . No multi-absorption edge or CL band splitting was observed, indicating the phase purity of the films and was confirmed by XRD analysis. The surface quality of the films has improved with the increase in Mg content. To the best of our knowledge, the current result shows the highest Mg content ( x =0.51), high quality, single phase wurtzite MgZnO epitaxial film ever grown by MOCVD. This is realized due to the non-equilibrium behavior of PMOCVD in which radicals that are formed during the growth process will have insufficient time to reach equilibrium.

The authors report on high spectral responsivity (SnxGa1 − x)2O3 Schottky UV photodetectors grown by plasma-assisted molecular beam epitaxy on β-Ga2O3 substrates. Schottky devices exhibited peak responsivities ranging from 49 to 194 A/W, with peak responsivity and wavelength position increasing systematically for higher Sn concentration from x = 0.01 to 0.18. Dark currents for the devices ranged from

It is long recognized that the effective surface clean is critical for the increased performance of solar cell and semiconductor devices. In this contribution, we introduced the effectiveness of crystalline silicon surface clean by a simple ultraviolet-ozone (UVo) process by comparing it against the industry standard RCA and UV assisted deionized water (DiO 3 ) techniques. Despite being simple, UV-ozone cleaning results in an effective surface passivation quality that is comparable to both RCA and DiO 3 clean, i.e., saturation current density (J 0 ) of 7 fA/cm2 compared to 5 fA/cm2 and 8 fA/cm2. In addition to the surface clean, we presented that both UVo and DiO 3 oxides can be used as a highly-quality chemical passivation to the crystalline silicon substrate, but with UVo oxide offering an improved passivation than DiO 3 oxide. Incorporating the UV}o oxide in between the interface of silicon and aluminum oxide or silicon nitride reduces J 0 by $\gt 50$%, compared to the interface without the UVo oxide.

Metal induced recombination (i.e., contact recombination) is a significant loss mechanism for homojunction crystalline silicon solar cells. In this work, a method is proposed to extract the metal induced recombination parameters using high- resolution photoluminescence PL imaging. By calculating the voltage distribution profile between fingers, the total current flow from the semiconductor to the finger, per area, can be obtained. The total recombination current at the semiconductor area and the metal contact area are then calculated and used to calculate the reverse saturation current for each region. The metal induced reverse saturation current $(j_{0m})$ is then obtained. This measurement allows the extraction of $j_{0m}$ on finished solar cells without the need to make special metal test structures. This is a big advantage over existing methods.

The emergence of conductive gallium oxide single crystal substrates offers the potential for vertical Schottky detectors operating in the UV-C spectral region. We report here on our recent work in the development of Tin Gallium oxide (TGO) thin film metal-semiconductor-metal (MSM) and Schottky detectors using plasma-assisted molecular beam epitaxy on c plane sapphire and bulk Ga2O3 substrates. Tin alloying of gallium oxide thin films was found to systematically reduce the optical band gap of the compound, providing tunability in the UV-C spectral region. Tin concentration in the TGO epilayers was found to be highly dependent on growth conditions, and Ga flux in particular. First attempts to demonstrate vertical Schottky photodetectors using TGO epilayers on bulk n-type Ga2O3 substrates were successful. Resultant devices showed strong photoresponse to UV-C light with peak responsivities clearly red shifted in comparison to Ga2O3 homoepitaxial Schottky detectors due to TGO alloying.

In this paper, the optical properties and microstructure of titanium oxide (TiO $_x$ ) thin films deposited by in-line atmospheric pressure chemical vapor deposition (APCVD) are tailored to act as effective antireflection coatings (ARCs) in crystalline silicon solar cells. The ability to control the crystalline phase, microstructure, and optical properties of these TiO $_x$ films by varying the deposition conditions is demonstrated. Because the refractive index of TiO $_x$ can be widely varied by changing the deposition temperature, these films can be applied as single- or double-layer ARCs (DLARCs) in crystalline silicon solar cells featuring a thin front-side passivation layer (e.g., thermal silicon oxide, aluminum oxide) or as a rear-side capping layer in rear passivated cells. Reflectance measurements on oxide-based DLARCs deposited on anisotropically textured monocrystalline Si wafers are presented for unencapsulated samples, along with the modeled performance of similar structures encapsulated in ethylene-vinyl acetate under varying angles of incidence. In the experiments on unencapsulated samples, two of the oxide-based DLARCs outperform a standard SiN $_x$ ARC, and all four outperform the SiN $_x$ ARC when encapsulated.

This paper describes the characteristics of damage, introduced under different conditions of diamond wire sawing, on the Si wafer surfaces. The damage occurs in the form of frozen-in dislocations, phase changes, and microcracks. The in-depth damage was determined by conventional ways such as TEM, SEM and angle-polishing/defect-etching, which only provide local information. We have also applied a new technique based on sequential measurement of the minority carrier lifetime after etching thin layers from the surfaces to determine average damage depth and its in-depth distribution. The lateral spatial damage variations, which seem to be mainly related to wire reciprocation process, were observed by photoluminescence and lifetime mapping. Our results show a strong correlation of damage depth on the diamond grit size and wire usage.

Passivation quality of silicon nitride (SiNx), aluminum oxide (AlOx) and a stack of AlOx/SiNx has been investigated in the presence and absence of a thin silicon oxide (SiOx) layer formed using ozonated deionized water. Lifetime measurements show $\approx 3$ ms effective carrier lifetime $(\tau_{eff})$ for the stack of AlOx/SiNx in the presence of the oxide. Low saturation current density $(Jo)$ and interfacial trap density $(D_{it})$ confirm and explain the high $\tau_{eff}$ for this sample. The stack of AlOx/SiNx can offer excellent surface passivation because of both field-effect passivation and chemical passivation. Note that the presence of oxide also shows a crucial impact in achieving a good passivation.

Tunneling aluminum oxide (Al2O3) layers are proposed as a candidate for hole collecting passivated contacts. These ultra-thin Al2O3 films ($\approx 1.5\text{nm}$) are deposited on boron diffused ($113\Omega/\square$) hydrophilic surfaces to act as metal-insulator-semiconductor (MIS) contacts. Record values of emitter recombination current densities (35–40 fA/cm2) and contact resistivity ($\approx 15\mathrm{m}\Omega\cdot \text{cm}^{2}$) were measured for this type of contact. Most importantly, all of these processes are carried out using industrially relevant tools on Cz wafers with non-polished surfaces.

In this work, we present a transparent and relatively simple method of calculating the economic viability of a given metrology technique using a case study in crystalline silicon photovoltaic (PV) cell manufacturing. The case study used here is the in-line measurement of implied open-circuit voltage of wafers following the deposition of front and rear side passivation films, which occurs before screen-printing and firing when manufacturing rear passivated PV cells. Cost-benefit calculations are performed using a new freeware tool on the PV Lighthouse website. Here, we show the wafer rejection threshold point selected and the cost of the metrology have a strong influence on the ultimate profitability.

Manufacturing, shipping & handling, installation, and in-field loading of photovoltaic solar panels are common contributors to the creation of cracks within the cells of a panel. Many cracks initially cause little or no power loss in the panel, but such tightly closed cracks may open over time due to environmental forces, and cause significant power loss and even failure of the module. We developed a method, using the LoadSpot tool, to apply a mechanical load to a panel to temporarily open pre-existing cracks while also allowing for electroluminescence (EL) imaging and flash IV testing. The change in the IV and EL measurements upon loading provides a quantifiable metric that can be used to evaluate reliability and durability. Such Predictive Crack Opening (PCO) tests have value in assessing preexisting damage as well as in the correlation with the degradation due to cracked cells opening upon environmental chamber and cyclic loading. We performed finite element modeling and simulation to illustrate the stresses applied at different load and mounting conditions. We demonstrate a wide range of mechanical loading and stress testing with accompanying EL and IV measurements which not only show the narrative of damage and power loss through static mechanical load, environmental chamber testing, and cyclic loading, but also suggests potential improvements which can be made to the order of chamber and cyclic load testing within the IEC 61215 standard. next.

High quality germanium doped β-Ga2O3 epitaxial film was grown by PMBE technique and fabricated into a vertical type Schottky photodiode with a Pt/nGa2O3/n+Ga2O3(010) structure. The photodiode exhibited excellent rectifying characteristics with a turn on voltage ~ 1V and near zero bias leakage current ~ 100 fA. The photoresponse measurement showed a true solar blind sensitivity with cutoff wavelength ~260 nm and an out of band rejection ratio of ~104. A maximum responsivity of 0.09 A/W at 230 nm was measured at zero bias, corresponding to an external quantum efficiency of ~52 %. The time response of the photovoltaic diode is in the millisecond range and has no long-time decay component which is very common in the MSM photoconductive wide bandgap devices. The photodiode performance remains stable up to 300°C, suggesting its potential use for high temperature applications.

We report the fabrication and characterization of highly responsive ZnMgO-based ultraviolet (UV) photodetectors in the metal–semiconductor–metal (MSM) configuration for solar-blind/visible-blind optoelectronic application. MSM devices were fabricated from wurtzite Zn1–xMgx O/ZnO (x ∼ 0.44) thin-film heterostructures grown on sapphire (α-Al2O3) substrates and w-Zn1–xMgx O (x ∼ 0.08), grown on nearly lattice-matched lithium gallate (LiGaO2) substrates, both by radio-frequency plasma-assisted molecular beam epitaxy (PAMBE). Thin film properties were studied by AFM, XRD, and optical transmission spectra, while MSM device performance was analyzed by spectral photoresponse and current–voltage techniques. Under biased conditions, α-Al2O3 grown devices exhibit peak responsivity of ∼7.6 A/W at 280 nm while LiGaO2 grown samples demonstrate peak performance of ∼119.3 A/W, albeit in the UV-A regime (∼324 nm). High photoconductive gains (76, 525) and spectral rejection ratios (∼103, ∼104) were obtained for devices grown on α-Al2O3 and LiGaO2, respectively. Exemplary device performance was ascribed to high material quality and in the case of lattice-matched LiGaO2 films, decreased photocarrier trapping probability, presumably due to low-density of dislocation defects. To the best of our knowledge, these results represent the highest performing ZnO-based photodetectors on LiGaO2 yet fabricated, and demonstrate both the feasibility and substantial enhancement of photodetector device performance via growth on lattice-matched substrates. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

This work presents the results of a Pareto analysis of critical challenges for emerging manufacturing technologies in c-Si photovoltaics. By soliciting input from members of the PV RD (2) Cell Materials and Processing; (3) Module Integration; (4) Materials and Device Characterization; (5) Reliability and Durability (Measurements); and (6) Modeling and Simulation. Some sub-categories feature a large differential in scoring from the top challenge(s) to lower scored challenges (e.g. Module Integration, Modeling and Simulation), indicating topics of high interest. Other sub-categories feature a more evenly distributed level of prioritization (e.g. Cell Materials and Processing), indicating many high priority challenges within the same area. In total, 14 top critical challenges were identified for the six sub-categories, and a brief review for each of these is provided. As industry and academia seek R&D topics to help push for higher efficiencies and lower cost c-Si modules, this Pareto analysis can hopefully provide some objective insight into areas of high interest for the general PV community.

ZnMgO thin films were grown by Molecular Beam Epitaxy on closely-lattice-matched MgO substrates with a Radio-Frequency (RF) generated oxygen plasma. The impact on the cubic ZnMgO of oxygen flow rate and applied RF power was investigated under a high vacuum condition (1E-6 Torr). Optical Emission Spectroscopy identified active species in the plasma including O, O + , and O þ 2 . The emission intensity of these species was compared at oxygen flow rates ranging from 0.5 sccm to 2.5 sccm and applied RF powers from 150 W to 500 W. Plasma composition at operating conditions was determined by correlating changes in optical emission to changes in relative concentration of active species in the plasma. Atomic Force Microscopy and profilometry characterized changes in surface roughness and growth rate of produced films. Independently increasing flow rate and RF power increased growth rate while simultaneously decreasing roughness. Growth rate enhancement of 80% was achieved with an improvement in surface roughness from 7.5 nm to 3.3 nm in a 1 lm square. Optimal conditions are discussed for ZnMgO thin film epitaxy. 2013 Published by Elsevier B.V.

We report on the growth of epitaxial Co3O4 (1 1 1) thin films by close injection showerhead (CIS)-MOCVD on sapphire substrates (c-, a- and r- planes). The deposition was carried out by using tri-dipivaloylmethanato-cobalt (Co(dpm)3) as precursor for Co and pure O2 or H2O vapor as oxidant. The effects of growth conditions, including Co(dpm)3 vaporization temperature, substrate temperature, O2/H2O flow rates, growth pressure and substrate orientation on the growth of the Co3O4 thin films were investigated. The crystallinity, phase purity and surface morphology of the films were studied by XRD, Raman and UV-visible spectroscopies, RHEED, SEM, and AFM. The as-grown films were found to be pure (1 1 1) oriented normal spinel type epitaxial Co3O4 thin films. The morphology of the films was strongly dependent on the identity of oxygen source used. Films grown using pure oxygen showed strongly faceted structures while those grown using H2O were dominated by porous interwoven and nanostructured films. The size and density of the faceted surface are strongly dependent on the growth rate of the films, controlled by adjustment of growth parameters. High growth rates resulted in small and dense grains. The growth of Co3O4 (1 1 1) was only successful on the a- and c-plane sapphire substrates, with no indication of nucleation and growth on r-plane sapphire substrates. Under otherwise identical growth conditions, the growth rate of films grown using H2O vapor was found to be 5 times higher than when using pure oxygen. These results demonstrate that Co(dpm)3 is a viable source for Co3O4 thin film growth by MOCVD, with resultant film morphology being highly dependent on the oxygen source and growth parameters.

We report on tin gallium oxide ((Sn x Ga1−x)2O3) solar-blind metal–semiconductor–metal (MSM) photodetectors grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates with varying tin content up to X Sn =10%. Incorporation of Sn into Ga2O3 was found to shift the optical bandgap of the epilayers from 5.0 eV (248 nm) for 0% Sn to 4.6 eV (270 nm) for 10% Sn content. Varying of the Sn concentration was also found to enable controlled tuning of the peak responsivity and cutoff wavelengths of MSM devices fabricated from the epilayers, with peak responsivity ranging from 0.75 A/W to nearly 16 A/W as the Sn concentration was increased from 0% to 10%. The high responsivity is attributed to photoconductive gain that increases for higher Sn concentrations and is accompanied by a slowing of the temporal response of the MSM detectors.

We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-time decay component which is common in photoconductive wide bandgap devices.We report on a high performance Pt/n−Ga2O3/n+Ga2O3 solar blind Schottky photodiode that has been grown by metalorganic chemical vapor deposition. The active area of the photodiode was fabricated using ∼30 A thick semi-transparent Pt that has up to 90% transparency to UV radiation with wavelengths < 260 nm. The fabricated photodiode exhibited Schottky characteristics with a turn-on voltage of ∼1 V and a rectification ratio of ∼108 at ±2 V and showed deep UV solar blind detection at 0 V. The Schottky photodiode exhibited good device characteristics such as an ideality factor of 1.23 and a breakdown voltage of ∼110 V. The spectral response showed a maximum absolute responsivity of 0.16 A/W at 222 nm at zero bias corresponding to an external quantum efficiency of ∼87.5%. The cutoff wavelength and the out of band rejection ratio of the devices were ∼260 nm and ∼104, respectively, showing a true solar blind operation with an excellent selectivity. The time response is in the millisecond range and has no long-ti...

Cubic ZnMgO films were grown by plasma-enhanced molecular beam epitaxy on MgO substrates. Interdigitatal metal–semiconductor–metal contacts were fabricated with Ni/Mg/Au to investigate the effect of growth temperature and source flux ratio on UV sensor properties. Device spectral responsivity was found to decrease with increasing Mg content, while UV–visible rejection ratio correspondingly increased. Peak responsivities ranged from 236 nm to 260 nm, spanning from 10 mA/W in the single crystal, high Mg case to ∼500 A/W for phase segregated films. UV–visible rejection ratios increased with increasing Mg content to three orders of magnitude. Solar blind detectors were realized with single-crystal ZnMgO, while effective visible blind detectors were made with phase-segregated ZnMgO films.

Using a high throughput, in-line atmosphere chemical vapor deposition (APCVD) tool, we have synthesized amorphous aluminum oxide (AlOx) films from precursors of trimethyl-aluminum (TMA) and O2, yielding a maximum deposition 150 nm min–1 per wafer. For p-type crystalline silicon (c-Si) wafers, excellent surface passivation was achieved with the APCVD AlOx films, with a best maximum effective surface recombination velocity (Seff,max) of 8 cm/s following a standard industrial firing step. The findings could be attributed to the existence of large negative charge (Qf ≈ –3 × 1012 cm–2) and low interface defect density (Dit ≈ 4 × 1011 eV–1 cm–2) achieved by the films. This data demonstrates a high potential for APCVD AlOx to be used in high efficiency, low cost industrial solar cells. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO thin films were grown on Zn-polar non-miscut ZnO substrates by plasma-assisted molecular beam epitaxy (PAMBE). With an electrostatic ion trap applied to the oxygen plasma source, the etching effect by plasma was significantly reduced. Atomically flat surfaces with one monolayer step height along the [0 0 0 1] direction were achieved at a low growth temperature of 610 °C. Good surface morphology with root mean square (RMS) roughness as small as 0.16 nm was achieved. High oxygen plasma power and low Zn flux were necessary to achieve a step-flow growth mode with a homogeneous surface morphology. It was found that the growth rate and surface RMS roughness decreased with increased growth temperature.