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• A multi-stack oxide layer (Al 2 O 3 /HfO 2) is applied at the front interface of CIGS. • A multi-stack design is used to prevent unwanted etching of Al 2 O 3 during the CBD. • A bottom-up (BU) and a top-down (TD) approach is used to create contact openings. • A NaCl template patterning was used to create a pattern on the CIGS or AlOx surface. • The TD approach shows more promising results for the front interface applications. The implementation of an oxide layer with contact openings to the Cu(In,Ga)Se 2 (CIGS) interfaces has become especially popular to reduce the recombination losses, resulting in a higher open-circuit voltage. While implementing this approach on the back surface is straightforward, it is more complicated for the front surface due to the roughness of the absorber as well as material selection constraints imposed by further processing steps. In this contribution, an AlO x /HfO x multi-stack oxide layer with contact openings is applied between the CIGS and CdS layers. Two different approaches to create contact openings in multi-stack oxide layer are presented, and their advantages and disadvantages are investigated. In the bottom-up approach (BU), a NaCl salt pattern is created on the CIGS absorber surface, while in the top-down approach (TD), the pattern is created on the AlO x layer surface. Time-resolved photoluminescence (TR-PL) shows that the multi-stack design improves the PL decay time regardless of the approach, but when the CdS layer is deposited, the PL decay time decreases. A more severe decrease is observed in case of the BU approach. Capacitance-Voltage measurements show that there is no impact on doping level when the NaCl pattern is created on an AlO x surface. This work shows that any oxide material, even if not chemically resistant to the chemical bath deposition, can be applied at the CIGS/buffer layer interface, and additionally, any template can be used to create contact openings while preventing interaction between the material used for patterning and the CIGS, using the TD approach. [ABSTRACT FROM AUTHOR]

We report X-ray measurements on a prototype 1.1 cm2, 32×32 GaAs pixel array with a pixel size of 350×350 μm2 produced to assess the technological feasibility of making large area, almost Fano-limited arrays, which operate near room temperature. Measurements were carried out on four widely separated pixels both in our laboratories and using monochromatic X-ray pencil beams at the HASYLAB synchrotron research facility in Hamburg, Germany. The pixels were found to be very uniform both in their energy and spatial responses. For example, typical energy resolutions of ∼280 eV at 10.5 keV, rising to ∼560 eV at 60 keV were achieved. The corresponding resolutions measured under full-pixel illumination were found to be the same within statistics, indicating uniform crystallinity and stoichiometry. Likewise, by scanning a 15 keV, 15×15 μm2 beam across the entire surface of each of the pixels, the gain uniformity across the pixels (and by implication the entire array) was determined to be statistically flat. [Copyright &y& Elsevier]

We summarise the results of a number of X-ray measurements on a 7 mm2, 0.5 mm thick HgI2 detector carried out both in our laboratory and at two synchrotron radiation facilities in Germany. The detector energy response function was found to be linear over the energy range 2.3–100 keV with an average rms non-linearity of 0.2%. Using a 50×50 μm2 15 keV monoenergetic X-ray beam, the spatial uniformity of the detector response was determined by a raster scan technique to be better than 1%. At room temperature, the FWHM energy resolution was 600 eV at 5.9 keV rising to 6 keV at 100 keV with no statistically significant difference between pencil beam (50×50 μm2) and full-area illumination. It was found that the FWHM energy resolution decreased with decreasing temperature reaching a minimum of 400 eV for 5.9 keV X-ray illumination at −19.2°C. Below this temperature, the FWHM begins to rise slowly. By considering the various contributions to the FWHM energy resolution, we estimate the charge collection efficiency to be (95.2±0.7)% at room temperature and (98±0.2)% at −19°C with a Fano factor of 0.30±0.24 at room temperature. [Copyright &y& Elsevier]

In this work, hafnium oxide layer is investigated as rear surface passivation layer for ultra-thin (550 nm) CIGS solar cells. Point contact openings in the passivation layer are realized by spin-coating potassium fluoride prior to absorber layer growth. Contacts are formed during absorber layer growth and visualized with scanning electron microscopy (SEM). To assess the passivating qualities, HfOx was applied in a metal-insulator-semiconductor (MIS) structure, and it demonstrates a low interface trap density in combination with a negative density of charges. Since we used ultra-thin devices that are ideal to probe improvements at the rear, solar cell results indicated improvements in all cell parameters by the addition of 2 nm thick HfOx passivation layer with contact openings. [ABSTRACT FROM AUTHOR]

In ultrathin Cu(In,Ga)Se2 (CIGS) film solar cells, the CdS/CIGS interface may become one of the limiting factors for efficiency. The first step toward reducing the impact of this problem could be a surface treatment process to improve the quality of the front interface. The purpose of this study is to have a better understanding of the effect of wet chemical surface treatment, using ammonium sulfide ((NH4)2S), on CIGS thin film layers with different Cu/(Ga + In) (CGI) ratios. Herein, photoluminescence (PL) and time‐resolved PL (TRPL) studies are conducted on bare CIGS, ammonium sulfide–treated CIGS thin films, and samples with CdS. In bare CIGS, CGI ratio–dependent changes in PL are observed on both a low‐energy (defect related transition) and a high‐energy peak (band‐to‐band transition). After the surface treatment, the PL maximum increases by factors ranging from 4 to 11 depending on the CGI ratio, accompanied by a slower decay. Trends with similar improvement as in the PL study are observed in the performance of the solar cells. It is shown that the impact of the surface treatment is beneficial independently of the CGI ratio of the absorber layers. In all cases, the treatment is shown to improve the efficiency. [ABSTRACT FROM AUTHOR]

• Novel and industrially relevant rear surface passivation approach for CIGS ultra-thin solar cells. • Atomic-layer-deposited Al 2 O 3 is used as a passivation layer. • Spin-coated alkali solution is used to create point contacts. • Top-view SEM image of point contacts and supportive EDS analysis is presented. • A significant increase in open-circuit voltage is achieved. In this work, an industrially viable and novel rear surface passivation approach for Copper Indium Gallium di-Selenide, Cu(In,Ga)Se 2 , CIGS, ultra-thin (500 nm) solar cells is developed. The passivation layer was deposited by atomic layer deposition (ALD), and an alkali treatment was applied via spin coating. It was observed that selenization of the samples is required to create contact openings. The openings were visualized by SEM, and these results were supported by EDS. The impact of the oxide layer's thickness, as well as the alkali solution's molarity, was studied. Solar cells were produced for the optimal combination of these two parameters. As a result, with a relative 13% increase, the highest V oc of 623 mV was achieved. Hence, the efficiency of the passivated solar cell was relatively increased by one-third, by using an industrially feasible, fast, and repeatable technique. [ABSTRACT FROM AUTHOR]

• Single phase (Ag x Cu 1−x) 2 ZnSn(S,Se) 4 monograins were synthesized in molten flux. • Adding Ag to CZTSSe increases carrier concentration and decreases carrier lifetime. • Low Ag contents (x ≤ 0.02) in CZTSSe lead to higher solar cell device efficiencies. • The Ag incorporation changed the dominant radiative recombination channel in CZTSSe. • The Ag incorporation decreased the collection width as evaluated by the EBIC study. The open circuit voltage (V OC) deficit of Cu 2 ZnSn(S,Se) 4 (CZTSSe) kesterite solar cells is higher than that of the closely related Cu(InGa)Se 2 solar cells. One of the most promising strategies to overcome the large V OC deficit of kesterite solar cells is by reducing the recombination losses through appropriate cation substitution. In fact, replacing totally or partially Zn or Cu by an element with larger covalent radius one can significantly reduce the concentration of I–II antisite defects in the bulk. In this study, an investigation of the impact of partial substitution of Cu by Ag in CZTSSe solid solution monograins is presented. A detailed photoluminescence study is conducted on Ag-incorporated CZTSSe monograins and a radiative recombination model is proposed. The composition and structural quality of the monograins in dependence of the added Ag amount are characterized using Energy Dispersive X-ray Spectroscopy and X-Ray Diffraction method, respectively. The Ag-incorporated CZTSSe monograin solar cells are characterized by temperature dependent current-voltage and electron beam induced current methods. It was found, that low Ag contents (x ≤ 0.02) in CZTSSe lead to higher solar cell device efficiencies. [ABSTRACT FROM AUTHOR]

Abstract KF and NaF treatments were done for single-stage co-evaporated CuIn 0.7 Ga 0.3 Se 2. The absorber layers were grown on a substrate with an alkali barrier layer and NaF was either added before or after absorber layer growth. No differences were found on the device performance amongst the procedures to add Na. This is expected if the single-stage process does not have a copper rich stage or a Ga gradient, which is likely since there was no change of the elemental fluxes during absorber layer growth and no Ga profile was measured. KF was added by post-deposition only. Current-voltage characteristics were measured and net doping concentrations were determined from capacitance-voltage measurements (CV). We see an improvement of the open-circuit voltage (V oc) with increasing KF amount, and a marginal increase of the fill factor. CV measurements showed increasing net acceptor concentration with increasing KF amount. Time resolved photoluminescence (PL) showed an increased decay time for KF treated cells and the PL peak shape changed. Without KF treatment the PL peak is symmetric, after KF treatment a further peak appears at higher energy in the PL spectrum. This higher energy peak increases in intensity with increasing KF concentration. The same effects were seen in a sample without Na, but here the V oc was limited due to large tailing. Hence both Na and K are required for good cell efficiencies. Highlights • Thin ~500 nm CIGS solar cells were prepared by 1-stage co-evaporation. • Na an K alkali treatments were investigated pre- and post-deposition of the absorber layer. • KF treatment is performed in N 2 atmosphere. [ABSTRACT FROM AUTHOR]

Abstract Reducing the absorber layer thickness below 1 μm for a regular copper indium gallium di-selenide (CIGS) solar cell lowers the minimum quality requirements for the absorber layer due to shorter electron diffusion length. Additionally, it reduces material costs and production time. Yet, having such a thin absorber reduces the cell efficiency significantly. This is due to incomplete light absorption and high Molybdenum/CIGS rear-surface recombination [ 1 ]. The aim of this research is to implement some innovative rear surface modifications on a 430 nm thick CIGS absorber layer to reduce both these affects: an aluminium oxide passivation layer to reduce the back-surface recombination and point contact openings using nano-particles for electrical contact. The impact of the implementation of all these rear-surface modifications on the opto-electrical properties of the CIGS solar cell will be discussed and analyzed in this paper. Highlights • Rear surface passivation improves the open circuit voltage significantly. • Well defined nano-point contacts lead to high fill factors. • Unoptimized silver in the absorber affects cell performance. [ABSTRACT FROM AUTHOR]

The PEIE-ZnO nanocomposite thin film as a functional layer fabricated by using Spray on screen technology for the efficient large area organic light emitting diodes. [Display omitted] • PEIE incorporation on to ZnO nanoparticles reduced the surface traps on ZnO nanoparticles. • PEIE-ZnO nanocomposite acts as functional layers with electron injection, transport and hole blocking characteristics. • Stability of the OLEDs are determined by the type of electron injection/transport layer. • Spray on screen technology can fabricate the ultra-thin film layer PEIE-ZnO nanocomposite making the deposition roll to roll compatible. The charge carrier balance in organic light-emitting diodes (OLEDs) is crucial for optimizing external quantum efficiency (EQE). This is typically achieved by using charge injection and blocking layers deposited by vacuum deposition, which increases the fabrication time and cost. This study investigates the potential of polyethylenimine ethoxylated (PEIE), Zinc oxide (ZnO) nanoparticles and a PEIE-ZnO nanocomposite as functional layers for OLEDs with improved electron injection and hole blocking properties fabricated by solution processing. The PEIE-ZnO nanocomposite improves OLED performance: (a) a 28% increase in current density and enhanced electron mobility, (b) two times increase in electron mobility of the electron injection/transport layer, and (c) a reduction in surface and interface trap density. Consequently, the PEIE-ZnO nanocomposite shows an 84% increase in electroluminescence, 52.5% increase in luminous efficacy, 35.5% increment in external quantum efficiency, and increased stability as measured by degradation studies. Employing these interlayers fabricated by the novel and roll-to-roll compatible Spray-on-Screen deposition technique show a comparable OLED performance as that of spin coated and vacuum deposited electron injection layers, which makes the large area fabrication of optoelectronic devices with high efficiencies, high output, low cost, and long lifetime a possible reality. [ABSTRACT FROM AUTHOR]

Pure selenide Cu2ZnSnSe4 solar cells were fabricated with a maximum achieved open-circuit voltage ( VOC) of 454 mV, which is on par with the highest known VOC for this technology (Bourdais et al., Adv. Energ. Mater. 2016, 6). A simple, non-vacuum, spin coating technique was developed for the introduction of alkali ions (Li+, K+, Rb+) before two annealing steps. The presence of Rb and Li ions in particular, was observed to reduce recombination in the bulk and increase minority charge carrier decay time. This resulted in the reduction of the redshift in the photoluminescence peak from the bandgap and the VOC deficit. Bandgap variations and electrostatic potential fluctuations in conduction and valence bands were investigated as aspects likely affected by alkali ions. [ABSTRACT FROM AUTHOR]

Abstract: The integration of higher carrier mobility materials to increase drive current capability in the next CMOS generations is required for device scaling. But a fundamental issue regarding the introduction of high-mobility III–V in CMOS is the electrical passivation of the interface with the high-κ gate dielectric. In this work, we show that in situ H2S surface treatment on GaAs(001) leads to a stable and reorganized oxide/III–V interface. The exposition of the GaAs surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. Finally, MOS capacitors are fabricated to extract interface state density over the band gap. These results highlight a promising re-interest in chalcogenide passivation of III–V surfaces for CMOS applications. [Copyright &y& Elsevier]

Abstract: In this work we present an in situ investigation of the interface composition between an In0.53Ga0.47As substrate and an Al2O3 oxide grown by molecular beam deposition in ultra high vacuum conditions. In the effort to improve the chemical quality of the interface, reduction of semiconductor-oxygen bonding at the interface can be obtained by growing a few Å thick pure Al layer before starting exposure of the surface to the atomic oxygen flux. Conversely, when a Ge interface passivation layer is intercalated between the semiconductor and the oxide stack, the interface chemistry is governed by Ge reaction with other species (Al, O), leading only to a partial suppression of the interface oxides. [Copyright &y& Elsevier]

Abstract: A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(001) using molecular H2S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer. [Copyright &y& Elsevier]

Abstract: In this work we investigate the effect of different III–V surface passivation strategies during atomic layer deposition of Al2O3. X-ray photoelectron spectroscopy indicates that bare As-decapped and sulfur passivated In0.53Ga0.47As present residual oxides on the surface just before the beginning of the Al2O3 deposition while the insertion of a Ge interface passivation layer results in an almost oxide free Ge/III–V interface. The study of the initial growth regimes, by means of in situ spectroscopic ellipsometry, shows that the growth of Al2O3 on Ge leads to an enhanced initial growth accompanied by the formation of Ge–O–Al species thus affecting the final electrical properties of the stack. Alternatively, deposition on decapped and S-passivated In0.53Ga0.47As results in a more controlled growth process. The sulfur passivation leads to a better electrical response of the capacitor that can be associated to a lower oxide/semiconductor interface trap density. [Copyright &y& Elsevier]

Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide. [ABSTRACT FROM AUTHOR]