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Both nanosecond pulses and picosecond laser pulses are used for P2 patterning of chalcopyrite (Cu(In,Ga)Se2, CIGSe) and metal halide perovskite solar cell absorber layers. For CIGSe, the range of the modified material visualized by photoluminescence imaging is significantly wider than the actual physical linewidth, since energy input by the laser pulses leads to material modification in the vicinity of the scribed lines. This effect does not occur with the perovskite absorber layers, where there is no apparent influence on the edge regions. From numerical calculations of the temperature depth-profiles and the surface temperature distributions it is concluded that this effect is due to the significantly lower perovskite absorber layer thickness compared to CIGSe and the nevertheless significantly higher laser fluence required for perovskite ablation. The unaffected edge regions around the P2 line in the perovskite enabled a reduction of the dead area width in the fabrication of 3-segmented mini-modules, which could be significantly reduced from 430 to 230 µm, while increasing the aperture area power conversion efficiency and also the geometric fill factor, which could be increased up to 94.6%.

Laser-based fabrication of metal-halide perovskite mini-modules has recently been demonstrated using nanosecond (ns) laser pulses. However, it still suffers from high-resistance contacts due to remaining PbI2 residues at the bottom of the absorber-opening P2 scribe line. Therefore, in this study, we investigate the effect of shorter picosecond (ps) laser pulses, and thus lower heat input, on the complete removal of perovskite during P2 laser patterning to achieve low series resistances and thus improved electrical performances. Based on a systematic variation of the incident laser fluence and a comprehensive electrical, morphological and compositional analysis of the scribed area, optimal process windows for successful laser-based series interconnection are identified and evidenced by current density-voltage curves. The amount of PbI2 debris at the scribe bottom is reduced by using ps instead of ns pulses, resulting in improved j-V performance due to higher fill factor and lower series resistance. A numerical analysis of the laser-induced depth-dependent temperature profile shows that overcritical heating for both pulse durations induces explosive boiling of the excited volume, but only in the case of ns structuring the melting point of the underlying transparent oxide contact layer is exceeded. The corresponding scribed line morphology shows features of thermally-driven direct ablation (i.e., splashes), whereas ps pulses produce scribe lines with steep walls and delaminated areas, indicating a mechanical stress-assisted lift-off ablation. Accordingly, P2 laser patterning with ps pulses is recommended due to favorable morphological (steep edges) as well as composition-related (less PbI2 residues) scribe line properties.

To achieve a monolithic series interconnection of tandem solar cell devices consisting of a perovskite top cell and a CIGSe bottom cell, a two-terminal interconnection scheme is introduced that includes an additional, fourth patterning step, the so-called iso-cut, which separates the window layer stack between the two solar cells. The implementation of this interconnection scheme requires a process development for a total of four structuring steps, which was achieved by systematically varying the laser parameters. Based on a detailed characterization of the individual scribe line properties with respect to their scribe line depth, morphology, electrical functionality, chemical composition and their influence on adjacent and underlying layers, the optimal patterning parameters and suitable process windows were derived for each step, which is a prerequisite for a loss-free monolithic series interconnection in a tandem module.

P3 patterning with ns and ps laser pulses for monolithic series interconnection of perovskite solar cells was systematically investigated. The use of ns laser pulses generates a larger amount of PbI2 and a Br-rich interface layer in the processed area, which proved to be beneficial for P3 patterning due to improved defect passivation. Thus, the P3 step should be carried out with ns laser pulses for an optimized separation of adjacent cells, while ps laser pulses were recommended for the P2 interconnect. Accordingly, suitable laser parameters for optimal laser patterning are demonstrated and novel insights into the controversial issue about the influence of PbI2 on the overall photovoltaic performance of perovskite solar cells are presented.

Perovskite and CIGSe are suitable partners for tandem solar cells, since the bandgap energies of both materials can be precisely adjusted. The fabrication of series-interconnected CIGSe-perovskite tandem solar cells requires a re-design of the series interconnection scheme for single junction cells and the development of the corresponding laser parameters for patterning. In this contribution, we present such a concept based on the evolution of the standard P1-P3 patterning design to a four-scribe line scheme by adding an additional isolation-cut (iso-cut) to separate the conductive intermediate window layer stack. To realize this interconnection scheme, laser-based processes for each individual patterning step were developed and suitable process windows were identified and evaluated.

Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p i n type perovskite solar cell PSC with a 22.3 power conversion efficiency PCE . This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a synergy between 1 an improved perovskite absorber quality when introducing formamidinium chloride FACl as an additive in the triple cation Cs0.05FA0.79MA0.16PbBr0.51I2.49 Cs MAFA perovskite precursor ink, 2 an increased open circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride LiF interfacial buffer layer, and 3 high quality hole selective contacts with a self assembled monolayer SAM of [2 9H carbazol 9 yl ethyl]phosphonic acid 2PACz on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current density voltage, J V, measurements, substantial differences in device performance become apparent when considering longer term stability data. A reduced long term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal halide perovskite thin film deposition. Optimized devices maintained about 80 of the initial average PCE during maximum power point MPP tracking for gt;700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series interconnected mini modules with a PCE of 19.4 for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large area single junction and tandem modules based on PSCs

The upscaling of perovskite solar cells to modules requires the patterning of the layer stack in individual cells that are monolithically interconnected in series. This interconnection scheme is composed of three lines, P1‐P3, which are scribed using a pulsed laser beam. The P3 scribe is intended to isolate the back contact layer of neighboring cells. Previous research has shown that the P3 patterning is often affected by undesired effects such as back contact delamination, flaking, and poor electrical isolation, as laser‐material interactions are not yet fully understood. In this study, the influence of the laser pulse duration on the electrical and compositional properties of P3 scribe lines is investigated. The results show that both ns and ps laser pulses are suitable for P3 patterning, with the ns pulse leading to higher open circuit voltage, higher fill factor, and higher power conversion efficiency. It is found that the longer pulse duration resulted in a larger amount of PbI2 formed within the P3 trench. Next to the P3 line edge, the formation of a thin Br‐rich layer at the perovskite/hole transport layer interface was observed when ns laser pulses were used, which extends up to 12 µm into the active area of the module. Both the formation of PbI2 and a more Br‐rich perovskite layer effectively passivate defects at the edges of the scribe line and block charge carriers in its vicinity. It is concluded that ns laser pulses are preferable for P3 patterning as they promote the formation of beneficial chemical phases, resulting in an improved photovoltaic performance.

The upscaling of perovskite solar cells to modules requires the patterning of the layer stack in individual cells that are monolithically interconnected in series. This interconnection scheme is composed of three lines, P1–P3, which are scribed using a pulsed laser beam. The P3 scribe is intended to isolate the back contact layer of neighboring cells, but is often affected by undesired effects such as back contact delamination, flaking, and poor electrical isolation. Herein, the influence of the laser pulse duration on the electrical and compositional properties of P3 scribe lines is investigated. The results show that both nanosecond and picosecond laser pulses are suitable for P3 patterning, with the nanosecond pulses leading to a higher open circuit voltage, a higher fill factor, and a higher power conversion efficiency. It is found that the longer pulse duration resultes in a larger amount of PbI2 formed within the P3 line and a thin Br-rich interfacial layer which both effectively passivate defects at the scribe line edges and block charge carrier in its vicinity. Thus, nanosecond laser pulses are preferable for P3 patterning as they promote the formation of beneficial chemical phases, resulting in an improved photovoltaic performance. (Less)

Laser based patterning for monolithic serial interconnection of metal halide perovskite MHP solar cells is a key process for industrial manufacturing of large scale MHP solar panels. It requires reliable patterning process parameters to achieve low interconnection losses and, thus, high efficiencies. Here, P2 laser patterning of the perovskite layer was obtained by laser ablation using conventional nanosecond laser pulses at systematically varied laser fluences. The correlation of the laser impact to the morphology, composition, and electrical functionality was analyzed in detail by several surface analytical techniques. The occurrence of laser induced periodic surface structures and microdroplets at the bottom of the trenches indicates that material removal via stress assisted ablation is strongly influenced by thermal processes. The formation of PbI 2 containing residuals was evidenced, possibly causing contact resistance losses through the P2 interconnect. These results contribute to the identification of loss factors in laser based serial interconnection of perovskite solar cells and to further process optimization for upscaling to industrial module sizes

Laser-based patterning for serial interconnection of chalcopyrite (i.e., Cu(In ${}_{\rm{x}},\text{Ga}_{\rm{1-x}}$ )Se2 or CIGSe) solar cells was obtained by 1) laser ablation using picosecond (ps) pulses, 2) local phase transformation using nanosecond (ns) laser pulses, and 3) conventional needle-based patterning. All three patterning approaches cause a modification of the material properties in the vicinity of the actual P2 scribing lines, which affects and limits the electrical functionality of the interconnection, and thus has to be considered for positioning the P3 scribe. Thus, the extension and the properties of the affected zone aside the P2 scribe was investigated through spectral and spatial photoluminescence (PL). From the depletion of the PL intensity when approaching the scribing line and a peak shift analysis it is concluded that the laser-affected zone is distinctively larger than visual inspections suggest. Even putatively ultrashort, nonthermal ps pulses cause material modifications which might be facilitating recombination losses and thus limiting solar cell efficiencies. For ps laser patterning the affected area is even larger than for the ns laser patterning, due to a modification of the band structure and to thermal decomposition. Evolving subpeaks at the low energy tails are found to originate from Cu-related flat defect levels, i.e., Cu vacancies ( $V_{{\rm{Cu}}}$ ) and antisites (Cu In), created upon laser impact. These findings provide insights into laser-based material modification and provide beneficial information for minimizing the dead area resulting from laser-based monolithic interconnection.

Six advanced oxidation techniques were analyzed, evaluated and compared with respect to the preparation of high-quality ultra-thin oxide layers on crystalline silicon. The resulting electronic and chemical SiO 2 /Si interface properties were determined by a combined x-ray photoemission (XPS) and surface photovoltage (SPV) investigation. Depending on the oxidation technique, chemically abrupt SiO 2 /Si interfaces with low densities of interface states were fabricated on c-Si either at low temperatures, at short times, or in wet-chemical environment, resulting in each case in excellent interface passivation. Moreover, the beneficial effect of a subsequent forming gas annealing (FGA) step for the passivation of the SiO 2 /Si interface of ultra-thin oxide layers has been proven. Chemically abrupt SiO 2 /Si interfaces have been shown to generate less interface defect states.

The change of electrical conductivity in chalcopyrite (i.e., Cu(Inx, Ga1−x)Se2 or CIGSe) solar cells induced by nanosecond laser pulses is investigated as a function of the elemental composition and its spatial distribution. The underlying laser induced phase transformation process, which results in a decomposition of the CIGSe semiconductor and a modification of its elemental composition, is utilized to form the monolithic series interconnection between front and back contact in CIGSe based thin film solar cells. The results show a dependence of the composition of the CIGSe layer and the resulting series resistance on the applied laser fluence. Lower series resistance is primarily related to an enhanced fraction of copper, gallium and zinc in the laser transformed zone resulting from selective vaporization of absorber elements. For intermediate laser fluences (~0.36 J/cm2) a patterning process is established that allows reliable and high-quality series interconnection. Both, lower and higher laser fluences result in high series resistances due to incomplete phase transformation or damages of the back contact, respectively.

Surface sensitive methods, UV-VIS spectral ellipsometry (SE), surface photovoltage (SPV) measurements, and X-ray photoelectron spectroscopy (XPS) measurements were combined to investigate in detail the Si substrate oxidation and resulting interface electronic properties. Various wet-chemical oxidation methods utilizing hot deionized water with different HCl or Ozone content were optimized in order to prepare ultra-thin oxide layers with reproducible oxide thicknesses (ox > 0.3 to 3.5 nm), low values of interface state densities and well-defined interface charges. The simulation tool ELifAnT (Effective Lifetime Analysis Tool) was utilised to analyse experimental excess minority charge carrier density (Δn) dependent charge carrier lifetimes τeff (Δn), and to establish correlations between preparation induced interface charges Qit and defect densities Dit on both p-and n-type substrates.

Key steps in the fabrication of high-efficiency a-Si:H/c-Si heterojunction solar cells are the controlled pyramid texturing of the c-Si substrates to minimize reflection losses and the subsequent passivation by deposition of a high-quality a-Si:H layer to reduce recombination losses. This contribution reviews our recent results on the optimization of the wet-chemical texturing of crystalline Si wafers for the preparation of heterojunction solar cells with respect to low reflection losses, low recombination losses and long minority carrier lifetimes. It is demonstrated, that by joint optimization of both saw damage etch and texture etch the optical and electronic properties of the resulting pyramid morphology can be controlled. Effective surface passivation and thus long minority charge carrier lifetimes are achieved by deposition of intrinsic amorphous Si ((i) a-Si:H) layers. It is shown, that optimized (i) a-Si:H deposition parameters for planar Si (111) wafers can be transferred to a-Si:H layer deposition on random pyramid textured Si (100) wafers. Statistical analysis of the pyramid size distribution revealed that a low fraction of small pyramids leads to longer minority charge carrier lifetimes and, thus, a higher Voc potential for solar cells.

Solar cells incorporating metal-halide perovskite (MHP) semiconductors are continuing to break efficiency records for solution-processed solar cell devices. Scaling MHP-based devices to larger area prototypes requires the development and optimization of scalable process technology and ink formulations that enable reproducible coating results. It is demonstrated that the power conversion efficiency (PCE) of small-area methylammonium lead iodide (MAPbI3) devices, slot-die coated from a 2-methoxy-ethanol (2-ME) based ink with dimethyl-sulfoxide (DMSO) used as an additive depends on the amount of DMSO and age of the ink formulation. When adding 12 mol% of DMSO, small-area devices of high performance (20.8%) are achieved. The effect of DMSO content and age on the thin film morphology and device performance through in situ X-ray diffraction and small-angle X-ray scattering experiments is rationalized. Adding a limited amount of DMSO prevents the formation of a crystalline intermediate phase related to MAPbI3 and 2-ME (MAPbI3-2-ME) and induces the formation of the MAPbI3 perovskite phase. Higher DMSO content leads to the precipitation of the (DMSO)2MA2Pb3I8 intermediate phase that negatively affects the thin-film morphology. These results demonstrate that rational insights into the ink composition and process control are critical to enable reproducible large-scale manufacturing of MHP-based devices for commercial applications. (Less)

Laser-based patterning of CIGSe solar cell absorber layers for monolithic series connection by nanosecond (ns) and picosecond (ps) laser pulses introduces material modifications in the vicinity of the patterned lines, which affect the CIGSe composition, the electrical properties, the extent of the dead area and finally the efficiency of the complete solar cell. Here, spectral and time-resolved photoluminescence is used to show that Cu vacancies and anti-sites are formed next to the edges of the scribe lines, which lead to the formation of additional energy states in the band gap near the valence band edge. A significant reduction in charge carrier lifetime is noted as the scribed lines are approached from unaffected areas of the material. Since this effect is absent in the mechanical needle patterning, it can clearly be attributed to the influence of the laser pulses. Despite the laser-induced material modification, laser-based CIGSe patterning outperforms needle-based patterning. Advantages regarding the width of the affected edge areas were observed when using ns pulses instead of ps pulses, which could be due to the lower peak intensities.

Magnéli-type vanadium oxides form the homologous series VnO2n-1 and exhibit a temperature-induced, reversible metal–insulator first order phase transition (MIT). We studied the change of the adhesion force across the transition temperature between the cleavage planes of various vanadium oxide Magnéli phases (n = 3 … 7) and spherical titanium atomic force microscope (AFM) tips by systematic force–distance measurements with a variable-temperature AFM under ultrahigh vacuum conditions (UHV). The results show, for all investigated samples, that crossing the transition temperatures leads to a distinct change of the adhesion force. Low adhesion corresponds consistently to the metallic state. Accordingly, the ability to modify the electronic structure of the vanadium Magnéli phases while maintaining composition, stoichiometry and crystallographic integrity, allows for relating frictional and electronic material properties at the nano scale. This behavior makes the vanadium Magnéli phases interesting candidates for technology, e.g., as intelligent devices or coatings where switching of adhesion or friction is desired.

P2 laser patterning of the perovskite layer for serial monolithic integration was systematically investigated by laser ablation using nanosecond laser pulses at varied laser fluences. The correlation of the laser impact to the morphology, composition and electrical functionality was analyzed in detail by several surface-analytical techniques. It is found that material removal via stress-assisted ablation is strongly influenced by thermal processes. The formation of PbI 2 containing residuals was evidenced, presumably causing contact resistance losses through the P2 interconnect. From these results loss factors in laser-based serial interconnection of perovskite solar cells were identified, allowing for process optimization for upscaling to industrial module sizes.

Ultrathin oxide layers on crystalline silicon (c-Si) were prepared by different wet-chemical, plasma- and thermal oxidation techniques. The resulting electronic and chemical SiO 2 /Si interface properties were analyzed, compared and evaluated by combined x-ray photoemission (XPS) and surface photovoltage (SPV) measurements. Depending on the oxidation technique, chemically abrupt SiO 2 /Si interfaces (suboxide amounts $ 2 /Si interfaces are able to generate low interface defect states densities.

We analyze the influence of different oxidation methods on the chemical passivation quality of silicon oxide-nanolayers on crystalline silicon wafers with surface photo voltage and quasi-steady-state photo conductance measurements. We present a simple method by means of rapid thermal oxidation (RTO) and subsequent annealing in forming gas, which requires no complex surface pre-treatment or surface pre-conditioning after cleaning. This technique allows a reproducible preparation of high-quality ultra-thin oxide-nanolayers (1.3–1.6 nm) with a nearly intrinsic energetic distribution of interface states and a defect density of states of only 1 × 1012 cm−2 eV−1 at the minimum of the distribution. These results are compared with silicon oxide-nanolayers prepared by wet chemical oxidation and plasma oxidation where only a slight reduction of the interface defect density is achieved by subsequent anneal in forming gas environment. Furthermore, it is shown that applying the RTO oxide-nanolayer as an intermediate layer between Si and an a-SiNx:H layer, leads to a significant improvement of the surface passivation quality.

We report on the investigation and comparison of two different processing approaches for interdigitated back contacted silicon heterojunction solar cells our photolithography based reference procedure and our newly developed shadow mask process. To this end, we analyse fill factor losses in different stages of the fabrication process. We find that although comparably high minority carrier lifetimes of about 4 ms can be observed for both concepts, the shadow masked solar cells suffer yet from poorly passivated emitter regions and significantly higher series resistance. Approaches for addressing the observed issues are outlined and first solar cell results with efficiencies of about 17 and 23 for shadow masked and photolithographically structured solar cells, respectively, are presented

The deposition of thin and ultra-thin layers requires extremely clean, smooth and defect-free Silicon (Si) substrate surfaces as starting point. The preparation-induced surface micro-roughness and surface coverage of the substrates often affect the initial layer growth, the morphology or the adhesion of deposited layers. Si device fabrication includes multiple wet cleaning and etching steps involving different oxidizing and etching solutions, which modify the surface electronic properties according to fixed charges and defect states present on the surface. Depending on the details of the device structure, surface conditioning methods have to be carefully optimized to achieve the desired electronic interface properties.

Amorphous/crystalline heterojunction (a-Si:H/c-Si) solar cells on n-type substrates, textured in isopropanol (IPA)-free solution, with conversion efficiencies exceeding 20% are presented. These values represent a considerable improvement over our previously reported best cell efficiencies for cells with (i)a-Si:H buffer layer. They were achieved by thorough optimization of the surface texture, of the a-Si:H/c-Si interface passivation, and of the thickness of the intrinsic a-Si:H front layer, resulting in improved open-circuit voltages and fill factors. Thus, solar cells fabricated on IPA-free textured Si wafers can compete with those processed on wafers textured conventionally in IPA-containing alkaline solution and are an attractive alternative for industrial production due to their better process control, lower environmental impact and lower costs.

Liquid phase crystallization of silicon is a promising technology platform to grow multi crystalline silicon thin films on foreign substrates. For solar cell application it has already been demonstrated that open circuit voltages of up to 661 mV [1] and efficiencies of up to 15.9% [2] can be achieved on a silicon layer of a few microns only. However, while the quality of the material has been continuously improved, the cost factor of the utilized substrate has been given little attention. The present work focuses on the technology transfer from technical glass substrates to low cost soda-lime glass substrates to become more attractive for commercial applications. We demonstrate that despite a large difference in the expansion coefficient between soda lime glass and silicon absorber layer, adhesive silicon thin films can be produced under certain conditions. On these first layers, we were able to fabricate solar cells, which in their cell and material properties were only ~30% below the values of their technical glass counterparts.

Fabrication of Si nanodot single layers under ultrahigh vacuum (UHV) conditions is achieved by decomposition and self-organized growth from thermally deposited non-stoichiometric SiO x (x 2 capping layer due to phase separation upon appropriate in situ annealing. The kinetics of the thermal decomposition of the constituting Si suboxides (Si n+, n = 0…4) into Si nanodots and the surrounding SiO2 matrix is analyzed in situ by X-ray photoelectron spectroscopy (XPS) as a function of the annealing temperature. The maximum size and the density of the nanodots are varied by adjusting the stoichiometric coefficient x and the layer thickness. Thus, the electronic nanodot properties and the interlayer transport properties can be controlled. For initial compositions (x ranging from 0.9 to 1.4) and layer thicknesses (3 to 10 nm), phase separation was completed at 850 ℃. The phase separation revealed by XPS is directly correlated with electrical properties as derived from atomic force microscopy measurements detecting surface potentials (KFM) and local conductivity (CS-AFM) across individual nanodots.

All process steps in the fabrication of amorphous / crystalline (a-Si:H/c-Si) silicon heterojunction solar cells affect interface recombination and thus have an impact on the open circuit voltage of the final solar cell. Transient photoconductance decay is a convenient method to assess the charge carrier lifetime which is a direct measure for recombination and thus the interface quality. In this contribution we present a step-by-step analysis and evaluation of the charge carrier lifetime throughout the processing of the solar cells starting from the saw-damage etched Si wafer to the complete solar cell device. Particular emphasis is put on the optimization of the random pyramid texture. For this, surface morphologies and a-Si:H/c-Si interface properties were quantitatively evaluated and optimized with respect to low recombination and large carrier lifetimes. Based on this optimization a-Si:H/c-Si heterojunction solar cells with conversion efficiencies exceeding 20% were prepared on c-Si wafers textured in isopropanol(IPA)-free alkaline solution.

For further enhancement of solar energy conversion efficiency the passivation of silicon (Si) substrate surfaces and interfaces of Si-based solar cell devices is a decisive precondition to reduce recombination losses of photogenerated charge carriers. These losses are mainly controlled by surface charges, the density and the character of rechargeable interface states (Dit) [], which are induced by defects localised in a small interlayer extending over only few Å. Therefore, the application of fast non-destructive methods for characterization of the electronic interface properties directly during the technological process has received an increasing interest in recent years.

Lasers are increasingly being used as an efficient and reliable tool in the production of solar cells and solar modules. Particular interest exists in thin-film photovoltaics, where laser structuring is aimed to realize appropriate monolithic serial interconnection. A novel concept successfully demonstrated complete laser structuring by application of short nanosecond laser pulses with a single, visible wavelength. These results promise further simplification and flexibility to thin film solar cell production.

A theoretical model is developed to account for the kinetics of the decrease of the density of recombination active centres at the interface of SiO 2 layers with Si(111) substrates as a result of treatment by thermalised hydrogen plasma. The recombination active centres at the SiO 2 /Si interface are ascribed to be the P b centres. The model developed takes into account the kinetics of the incorporation of hydrogen atoms into the SiO 2 layer from the plasma source and their interaction with both passivated and unpassivated P b centres. A special attention is given to ultrathin (∼2 nm) SiO 2 layers. A simplification of the general model to this important case allows one to obtain analytical solution for the density of unpassivated recombination active P b centres as a function of the flow of hydrogen atoms from plasma, the initial density of P b centres, and the treatment time. The model applicability is verified comparing the results of calculations with the experimentally measured values of the relative density of recombination active centres at the ultrathin SiO 2 /Si(111) substrate interface upon passivation by atomic hydrogen from thermalised plasma source. A conformity of the model predictions to the experimental results is demonstrated.

A complete in situ process from preparation and hydrogen passivation to interface gap state analysis by near-UV photoelectron spectroscopy (NUV-PES) without breaking ultrahigh vacuum (UHV) conditions is applied to ultrathin oxide layers on Si(1 1 1), (1 1 0), and (1 0 0). RF plasma oxidation with thermalized neutral oxygen atoms allows the growth of homogeneous ultrathin SiO 2 layers ( 2 interfaces with minimal amounts of suboxides ranging from 2% on Si(1 0 0) to 4% on Si(1 1 0). The oxide growth is independent of the crystallographic orientation. Appropriate plasma treatment with nearly thermalized hydrogen atoms ( E kin 2 /Si interfaces and is most efficient on Si(1 0 0). In contrast, energetic hydrogen plasma treatment of these interfaces with kinetic energies exceeding 120 eV, which is conventionally applied for polycrystalline Si thin-film solar cells, imparts large amounts of energy and deteriorates the electrical properties as is reflected in interface degradation and increased densities of defect states.

SiO 2 /Si/SiO 2 single quantum wells (QWs) were prepared under ultrahigh vacuum conditions in order to study their structural, chemical and photoelectrical properties with respect to a possible application in photovoltaic devices. Amorphous silicon (a-Si) layers (thickness

Ultrasonic force microscopy (UFM) is used to resolve the elastic nanostructure of strained antimony (Sb) particles. These nanoparticles were formed by aggregation and spontaneous rapid crystallization of thermally deposited Sb onto the (0 0 0 1) basal planes of highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS2). UFM reveals clear contrast within individual nanoparticles, which can be attributed to differences in the local stiffness. This interpretation is confirmed by transmission electron microscopy (TEM) images, in which bending contours prove the existence of strained regions within the nanocrystals. r 2007 Elsevier B.V. All rights reserved. PACS: 61.16.Ch; 81.05.Ys; 61.16.Bg

Electrical and structural functionality of monolithic interconnection of CIGSe solar cells by P1–P3 picosecond laser ablation has been successfully established and evaluated as being competitive to conventional needle scribing. In all three patterning steps the material is selectively and completely removed yielding structurally well-defined trenches at high scribing speeds up to 1 m/s. P1 and P2 ps laser scribing clearly improves the solar cell efficiencies whereas P3 scribing is still challenging due to shunts resulting from laser-induced alteration of the absorber material.

We analyze the chemical passivation quality of silicon oxide-nanolayers on crystalline silicon wafers prepared by different oxidation methods with surface photo voltage and quasi-steady-state photo conductance measurements. It is shown that for wet chemical oxidation and plasma oxidation, adequate passivation of the interface defects is achieved by subsequent anneal in forming gas environment. Furthermore, we present a simple oxidation method by means of rapid thermal oxidation, which requires no complex surface pre-treatment or surface pre-conditioning after cleaning. By rapid thermal oxidation (RTO) in a gaseous mixture of argon and oxygen and subsequent anneal in forming gas, a reproducible preparation method of high-quality ultra-thin oxide-nanolayers with a nearly intrinsic energetic distribution of interface states and a defect density of states of only 1 × 1012 cm−2 eV−1 at the minimum of the distribution is demonstrated.

The thermal impact of nanosecond laser pulses was beneficially employed and well-controlled for the preparation of the P2 interconnect by local phase transformation (i.e., by drawing conductive lines rather than removing the material) in CIGSe mini-modules, which were demonstrated to outperform their conventionally needle-patterned counterparts. Conductivity and elemental composition of the scribed lines as well as the extent of the heat-affected area were analyzed, quantified and taken into account for achieving optimal CIGSe solar module performances. This approach opens new prospects for significant simplification of the serial interconnection, since the P2 und the P3 can be scribed simultaneously after deposition of both the CIGSe and the TCO layer.

The spontaneous formation of complex interfacial patterns from thermally deposited Sb4 clusters on HOPG is controlled by the deposition conditions (i.e., coverage and deposition rate) at constant t...

Overlayer structures can be formed on surfaces by the deposition of preformed clusters from the gas phase containing from only a few up to a few hundred atoms. By this method, nanostructures with novel chemical and physical properties can be stabilized. This article presents the results obtained using the simple molecular cluster Sb4 as the precursor for deposition and nanoparticle assembly on various surfaces, and under various conditions. A rich variety of phenomena is observed and discussed.

The growth of thin antimony films on the Au(1 1 1) surface at room temperature is studied by scanning tunneling microscopy (STM) in ultrahigh vacuum. At coverages up to one monolayer nanometer-sized islands are formed on the Au(1 1 1) terraces. High resolution STM images of these islands allow the distinction of gold and antimony atoms and confirm the formation of a well-ordered surface alloy. Its symmetry and interatomic distances agree well with the unreconstructed (1 0 0) plane of the bulk compound AuSb2. With increasing antimony coverage amorphous layers grow on the alloy support. In the initial stage of the amorphous layer growth ordered regions with cubic lattice structure are found in the overall amorphous films. The measured lattice constants and symmetries of these local structures imply that they consist of undissociated Sb4 clusters.

Sb4-clusters have been deposited onto highly oriented pyrolytic graphite (0001), and the formation of larger antimony particles has been observed as a function of surface coverage by SEM. The initial morphology of the particles is nearly spherical, according to a Volmer–Weber type growth. At a radius of about 60 nm this geometry becomes unstable, and the particles transform into dendritic and viscous finger-like islands. We suppose that the driving force for this conversion is due to a supercooling of the particles, which itself arises from a size dependent amorphous to crystalline phase transition.

The fragment ion-yield curves for the scattering of antimony cluster cations from highly oriented pyrolitic graphite show two clearly separated abundance maxima. On the low-energy side ( $\ensuremath{\le}150\ifmmode\pm\else\textpm\fi{}30\mathrm{eV}$) the interaction is characterized by the unimolecular fragmentation of the clusters and by neutralization as the competing process. The neutralization efficiency reaches a maximum at collision energies of $150\ifmmode\pm\else\textpm\fi{}30\mathrm{eV}$. Above this boundary a transition to two different processes is indicated by a change in the fragment ion distribution. These competing processes are here the shattering and the implantation of the clusters. The threshold for implantation depends significantly on cluster size.

We have investigated the interaction of positively charged antimony clusters Sb n + with HOPG as a function of cluster size (2 n