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Additive manufacturing transforms the landscape of modern microelectronics. Recent years have witnessed significant progress in the fabrication of 2D planar structures and free-standing 3D architectures. In this work, we present a much-needed intermediary approach: we introduce the Ultra-Precise Deposition (UPD) technology, a versatile platform for material deposition at micrometer scale on complex substrates. The versality of this approach is related to three aspects: material to be deposited (conductive or insulating), shape of the printed structures (lines, dots, arbitrary shapes), as well as type and shape of the substrate (rigid, flexible, hydrophilic, hydrophobic, substrates with pre-existing features). The process is based on the direct, maskless deposition of high-viscosity materials using narrow printing nozzles with the internal diameter in the range from 0.5 to 10 µm. For conductive structures we developed highly concentrated non-Newtonian pastes based on silver, copper, or gold nanoparticles. In this case, the feature size of the printed structures is in the range from 1 to 10 µm and their electrical conductivity is up to 40% of the bulk value, which is the record conductivity for metallic structures printed with spatial resolution below 10 µm. This result is the effect of the synergy between the printing process itself, formulation of the paste, and the proper sintering of the printed structures. We demonstrate a pathway to print such fine structures on complex substrates. We argue that this versatile and stable process paves the way for a widespread use of additive manufacturing for microfabrication.

This paper presents results of an empirical investigation on drop feature optimization, subsequent fine trace printing and influence of sintering atmosphere on printed traces on polyimide substrate with Ag nanoparticle ink. The impact of printing parameters such as waveform features, jetting voltage and printhead height on drop formation and fine trace printing is investigated. The experiments revealed that drop diameter decreased by 33% after decreasing jetting voltage and overall waveform duration to a minimum functional range. From further studies, it is found that to print accurate fine traces an optimum drop spacing value in consideration with drop count should be selected which prints traces close to the required trace width dimensions. Based on these optimizations, trace width of 30 ± 2 μm can be printed with minimum pitch of 35 μm. Sintering progresses faster under air compared to nitrogen due to the efficient removal of the organic capping agents. The resulting sheet resistance under air and nitrogen were 0.1312 Ω/π and 1.8586 Ω/π respectively.

Plasma-enhanced atomic layer deposited (PEALD) aluminum oxide (Al2O3) thin film were investigated with respect to their application in silicon solar cells where not only excellent surface passivation but also excellent electrical insulation properties are required. In this study, the insulation properties of about 10 nm to almost 250 nm Al2O3 thin films, deposited at temperatures in the range of 100 °C to 350 °C and annealed in the range of 250 °C to 450 °C, were correlated to various thin film properties, most notably the thin film defect density, i. e. pinhole density, and the thin film stress. Al2O3 thin films provide sufficient electrical insulation after a post-deposition annealing step at 450 °C when deposited at 250 °C with thickness of at least 80 nm which can be attributed to a low defect density and low stress in the thin films, allowing a low leakage current density and a high breakdown voltage that was independent of the type of metals used for the electrode. Al2O3 thin films deposited and annealed at these temperatures enabled a very good surface passivation of silicon. These results indicate that Al2O3 thin films realized by PEALD are a promising candidate for silicon solar cells that rely on passivating as well as insulating thin films.

A heterostructure of zinc oxide (ZnO) and single layer graphene is fabricated by sandwiching a transferred graphene between two thin ZnO films (∼20 nm each). ZnO thin films were grown using decomposition of Zn(acac)2 and spin-coating technique. Graphene transfer route with PMMA temporary carrier and metal etching process was used to transfer high quality commercial graphene from copper foil on the zinc oxide surface on glass. This novel and ultra-thin heterostructure (∼40 nm) is sensitive for UV illumination and works as a photodetector (PD). In this device, both positive and negative photoconductivity (PC) were observed depends on illumination intensity and spectrum of incident light. Relatively long response and recovery times obtained in ZnO/G/ZnO structure are related to the metastable defect states of ZnO and its interfaces with graphene and/or silver contacts. The obtained results show that the transferred single layer graphene sheet between thin ZnO films could be a novel route for improvement properties this low-cost metal oxide.

We present a comprehensive approach to print submicron conductive lines at unprecedented flexibility, accuracy, and low cost. We will discuss both the fundamental process of a guided assembly of nanoparticles and its implementation in the XTPL Submicron Lab Printer. Finally, we demonstrate a number of potential applications of this technology.

This paper is devoted to the development of standard and inverted polymer solar cells based on polyazomethine (PAZ-Car-TPA), poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM). We analyzed the influence of: (i) PEDOT:PSS or MoO 3 as a hole transporting layer in standard devices, (ii) aluminum doping level (from 0 to 3.7%) in ZnO (obtained by atomic layer deposition, ALD) applied as an electron transporting layer in inverted solar cells and (iii) the method applied to obtain ZnO layer (ALD or sol-gel) on its photovoltaic properties. The best device configuration is ITO/AZO (3% Al)/P3HT:PCBM/MoO 3 /Ag which exhibits a power conversion efficiency of 1.51% under about 100 mW/cm 2 AM 1.5 G simulated solar emission. Devices were additionally tested by electrochemical impedance spectroscopy. HOMO-LUMO levels of PAZ-Car-TPA and its mixture with HCl, H 2 SO 4 , p-toluenesulfonic acid, PEDOT:PSS and water were analyzed by cyclic voltammetry and quantum mechanical calculations using Density Functional Theory method.

Flexible films with high barrier properties against water and oxygen are currently in the focus for applications in an increasing number of technical fields, e.g. electronic and optical devices. In this research work, high performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the rigidity and thermal stability of inorganic materials. The main goal was to obtain low-cost and low-temperature barrier layer for flexible solar cells with high transparency and hydrophobic properties. Surface morphology and surface performance together with hydrophobic and optical properties were examined and compared for various samples. Moreover, some preliminary permeability tests were carried out for selected samples to indicate for some improvement in terms of barrier quality.

The laser chemical processing (LCP) technique for the local doping of crystalline silicon solar cells is investigated. Here, a liquid jet containing a dopant source acts as a waveguide for pulsed laser light, which results in the melting and subsequent doping of the silicon surface. Typical LCP pulse durations are in the 15 ns range, giving satisfactory results for specific parameter settings. While great potential is assumed to exist, optimization of the pulse duration has until now not been deeply investigated, because it is hard to change this parameter in laser systems. Therefore, this paper accesses the influence of the pulse duration by a simulative approach. The model includes optics, thermodynamics, and melt dynamics induced by the liquid jet and dopant diffusion into the silicon melt. It is solved by coupling our existing finite differences Matlab-code LCPSim with the commercial fluid flow solver Ansys Fluent. Simulations of axial symmetric single pulses were performed for pulse durations ranging from 15 ns to 500 ns. Detailed results are given, which show that for longer pulse durations lateral heat conduction significantly homogenizes the inhomogeneous dopant distribution caused by the speckled intensity profile within the liquid jet cross section. The melt expulsion by the liquid jet is low enough that a sufficiently doped layer remains after full resolidification for all pulse durations. Last, temperature gradients are evaluated to give an indication on the amount of laser damage induced by thermal stress.

The performance of n-type back-contacted back-junction silicon solar cells where the boron-doped emitter diffusion on the rear side is locally overcompensated by a phosphorus-doped base-type back surface field (BSF) diffusion has been analysed theoretically and experimentally. By overcompensating the emitter diffusion the noncollecting base-type region can be reduced significantly allowing electrical shading losses to be minimized. It has been found that for solar cells with a lowly doped BSF diffusion the local external quantum efficiency and the short-circuit current density Jsc could be improved significantly. For reference solar cells with an undiffused gap between emitter and BSF diffusion and a large noncollecting base-type region, a maximum Jsc of 40.9 mA/cm2 could be achieved and for solar cells with a locally overcompensated boron-doped emitter diffusion featuring a small noncollecting base-type region a maximum Jsc of 41.4 mA/cm2 has been measured. The reduction of Jsc losses caused by free carrier absorption (FCA) in highly doped silicon at near-infrared wavelengths is also shown. Furthermore, theoretical investigations are performed by one-dimensional device simulations and the influence of highly doped and lowly doped emitter and BSF diffusions on the open-circuit voltage Voc is presented. For solar cells with a locally overcompensated boron-doped emitter diffusion Voc could be improved from 629 to 652 mV when lowly-doped diffusions and thermally grown SiO2 and antireflection plasma enhanced chemical vapour deposited (PECVD) SiNx passivation stacks are applied. For the reference solar cells with an undiffused gap between the lowly doped emitter and BSF diffusions Voc of 693 mV could be achieved for a plasma enhanced atomic layer deposited (PEALD) Al2O3 passivation layer.

All-screen-printed back-contact back-junction silicon solar cells with aluminum-alloyed emitter on n-type base material were fabricated and analyzed at Fraunhofer ISE PV-TEC. Three different process sequences are compared to each other. One process flow with shallow phosphorus profiles realizes cells with efficiencies of 19.7%. Using a long thermal oxidation, cells with deep driven-in phosphorus profiles (front and back surface field) were processed where solar cell efficiencies of 20.0% are realized. Both cell efficiencies are independently measured at Fraunhofer ISE CalLab on a designated area of 16.65 cm2. The specific contact resistivity of screen-printed and fired silver paste to silicon surfaces with different phosphorus profiles was determined in dependence of several firing conditions. The main developed features of the presented cell structure comprise the firing-stable front and rear passivation layers, the spiking-free passivation layer against aluminum and the deep driven-in phosphorus profile that can be contacted by silver screen-printing paste in a firing step.

In this paper results for liquid media are presented, which are used the first time as liquid jet for cutting of silicon with laser chemical processing (LCP). The liquids contain a perfluoro-carbon compound as solvent and elemental chlorine as etching agent for silicon. Experiments were performed to investigate its influence on groove form and maximum achieved groove depth. It is shown that with the addition of low-concentration chlorine, the groove depth can already be significantly increased. The groove shape could be changed from a V-profile to a U-profile. Furthermore, an about four times greater groove depth was achieved by applying a saturated chlorine solution compared to groove depths without using chlorine. Finally, a theory is given and discussed to describe the phenomena observed.

The performance of n-type Si back-contact back-junction (BC-BJ) solar cells under illumination with high energy ultraviolet (UV) photons was investigated. The impact of the phosphorus doped front surface field (FSF) layer on the stability of the front surface passivation under UV illumination was investigated. Lifetime samples and solar cells without the front surface field showed a significant performance reduction when exposed to ultraviolet light. The surface saturation current density ( J 0e ) increased from 48 to 446 fA/cm 2 after the UV exposure. At the same time the efficiency of the BC-BJ solar cells without the FSF diffusion reduced from 19.8% to 14.3%. In contrast to the lifetime samples and solar cells without the FSF diffusion, the tested n + nn + structures and the BC-BJ solar cells with applied FSF diffusion profiles were significantly more stable under UV exposure, i.e. J 0e increased only by a factor of 25% and the efficiency of these cells decreased only 0.3% abs by the UV illumination. Finally it was shown that the performance of the UV-degraded solar cells without FSF could be improved during a forming gas anneal (FGA). Due to application of FGA the efficiency almost fully recovered from 14.3% to 19.6%.

First results showing the viability of combining laser chemical processing (LCP) and aerosol jet printing (AJP) technologies to produce a high-efficiency front side for silicon solar cells are presented. LCP simultaneously opens the anti-reflection coating (ARC) and highly dopes the underlying silicon to create a selective emitter, while AJP is the first in a two-step fine-line contact formation procedure. The electrical properties as well as the morphology of the resulting structures are presented. Performance similar to that achieved with evaporated TiPdAg metallization is demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.

The determination of the emitter saturation current density J0e of symmetrical test structures, analyzed by injection-dependent lifetime spectroscopy (IDLS), in high as well as in low injection regimes is compared. A detailed investigation of the influence of different models for the Auger recombination on the evaluation of the measured minority carrier lifetime is performed. It can be concluded that a good agreement for the extraction of J0e under high and low injection conditions for lightly and highly doped emitters on textured and untextured surfaces was obtained if the Auger parameterization of Kerr et al. is applied. For deep-diffused emitter profiles on textured surfaces a significant increase of J0e well above the geometrical surface area ratio of untextured and textured surfaces of 1.7 was observed. A verification of the experimentally determined values for J0e is performed by numerical device simulations. The simulated surface recombination velocity for the investigated emitter doping profiles is in good agreement to analytical calculations. Copyright © 2010 John Wiley & Sons, Ltd.

N-type back-contact back-junction solar cells were processed with the use of industrially relevant structuring technologies such as screen-printing and laser processing. Application of the low-cost structuring technologies in the processing of the high-efficiency back-contact back-junction silicon solar cells results in a drastic increase of the pitch on the rear cell side. The pitch in the range of millimetres leads to a significant increase of the lateral base resistance. The application of a phosphorus doped front surface field (FSF) significantly reduces the lateral base resistance losses. This additional function of the phosphorus doped FSF in reducing the lateral resistance losses was investigated experimentally and by two-dimensional device simulations. Enhanced lateral majority carrier's current transport in the front n+ diffused layer is a function of the pitch and the base resistivity. Experimental data show that the application of a FSF reduces the total series resistance of the measured cells with 3.5 mm pitch by 0.1 Ω cm2 for the 1 Ω cm base resistivity and 1.3 Ω cm2 for the 8 Ω cm base resistivity. Two-dimensional simulations of the electron current transport show that the electron current density in the front n+ diffused layer is around two orders of magnitude higher than in the base of the solar cell. The best efficiency of 21.3% was obtained for the solar cell with a 1 Ω cm specific base resistivity and a front surface field with sheet resistance of 148 Ω/sq. Copyright © 2008 John Wiley & Sons, Ltd.

One of the issues in the organic solar-cell technology that needs attention before mass production is its low long-term stability. These devices need often to be exposed to the light to improve their photovoltaic properties. This effect, known as light soaking, is the cause of challenges related to correct measurements and proper determination of the device lifetime. Lifetime determination and investigation of failure mechanisms of solar-cell devices require reliable measurement approaches. This paper presents the systematic studies on proper analysis of degradation dynamics of organic solar cells (OSCs) taking into account the light-soaking effect. Five groups of organic solar-cell annealed at various conditions (110°C to 170°C and nonannealed) were under investigation for 100 days. Measurement procedure for proper investigation of light-soaking effect is proposed. Solar-cell efficiency improvement, due to light-soaking effect, in range 8% to 27% was observed for as fabricated devices. After 100 days of study, the light soaking-related efficiency improvement increased up to over 100% of initial efficiency. Device lifetimes strongly depend on measurement methods, which were applied. Our results show the importance of taking into account the changes in magnitude of the light-soaking effect in measurements and degradation studies of OSCs.

In this study, back-contacted back-junction n-type silicon solar cells featuring a large emitter coverage (point-like base contacts), a small emitter coverage (point-like base and emitter contacts), and interdigitated metal fingers have been fabricated and analyzed. For both solar cell designs, a significant reduction of electrical shading losses caused by an increased recombination in the non-collecting base area on the rear side was obtained. Because the solar cell designs are characterized by an overlap of the B-doped emitter and the P-doped base with metal fingers of the other polarity, insulating thin films with excellent electrical insulation properties are required to prevent shunting in these overlapping regions. Thus, with insulating thin films, the geometry of the minority charge carrier collecting emitter diffusion and the geometry of the interdigitated metal fingers can be decoupled. In this regard, plasma-enhanced chemical vapor deposited SiO2 insulating thin films with various thicknesses and deposited at different temperatures have been investigated in more detail by metal-insulator-semiconductor structures. Furthermore, the influence of different metal layers on the insulation properties of the films has been analyzed. It has been found that by applying a SiO2 insulating thin film with a thickness of more than 1000 nm and deposited at 350 °C to solar cells fabricated on 1 Ω cm and 10 Ω cm n-type float-zone grown silicon substrates, electrical shading losses could be reduced considerably, resulting in excellent short-circuit current densities of more than 41 mA/cm2 and conversion efficiencies of up to 23.0%. Copyright © 2012 John Wiley & Sons, Ltd.

This work shows the possibility to use local laser chemical processing (LCP) boron dopings to create local back surface fields (LBSF) in a high efficiency p-type silicon solar cell structure. In order to create boron local back surface fields with LCP an alkaline aqueous boron solution was used. Our recent work shows the potential of this doping source to create local dopings with a surface concentration of about 1020 cm−3 and a doping depth of up to 1.3 μm. For the first time the successful application of boron LCP as LBSF for high efficiency solar cells is shown. The processed LCP-PERL (passivated emitter and rear locally diffused) solar cells show a maximum cell efficiency of η = 20.9% and an absolute cell efficiency benefit of Δη = 0.3–0.4%abs. in comparison to the reference cells with undoped local rear contacts processed with water-LCP. The presented solar cells show the best cell efficiencies ever achieved with LCP dopings. For this study different LCP-parameters were varied such as the contact geometry (line openings and openings formed with a cascade of overlapping LCP dots) and the pitch of the rear side contact structure. The results show that the LCP boron doping process allows the fabrication of industrial feasible local back surface field structures with a line contact design for high efficiency p-type silicon solar cells.

The investigation of different selective emitter (SE) approaches [1–3] is a current trend in solar cell manufacturing. The incorporation of a local high phosphorous doping underneath the front contact grid allows for the use of high-sheet resistance illuminated emitters that combine low recombination and improved blue response. Further efficiency increase compared to the standard screen-printed solar cell is achieved via plated contacts [4–5] that feature better aspect ratio and optical properties [6], higher line conductivity and smaller width [5] compared to screen-printed contacts. In this paper we present detailed technological requirements for next-generation front side metallization as well as experimental results of the RENA high-efficiency metallization cluster consisting of Laser Chemical Processing (LCP) and Ni-Ag light-induced plating (LIP). It becomes clear that efficiency on cell level is not the only figure of merit for a successful product and that the combination of SE with plating has a much higher potential for increasing cell efficiency than the metallization of SE via screen-printing.

Laser processing is an important application for fabrication of silicon solar cells, e.g. buried contacts, laser fired contacts or edge isolation. At Fraunhofer ISE a liquid-jet guided laser is used for Laser Chemical Processing (LCP). Both the fundamentals of laser material ablation with this system and the application of various processes for solar cell fabrication are investigated. The applications are divided into two main areas: Microstructuring and deep laser cutting (wafering) of silicon substrates. Microstructuring contains the investigation and characterization of laser induced damage and selective emitter formation for n- and p-type emitters depending on laser parameters and liquid properties. One of the most important and industrially relevant topics at the moment is the formation of a selective highly doped emitter under the metal fingers of solar cells. Wafering deals with the evaluation of suitable laser parameters, adequate chemicals or chemical additives and the understanding of ablation processes by simulation and experimental work. In this presentation newest results concerning n-type doping for varying laser and liquid parameters will be presented with regard to cell efficiency and contact resistance. Furthermore a short overview of promising LCP applications will be given, e.g. p-type doping and wafering.

The relation between current and illumination intensity of three structures of high-efficiency back-junction back-contact silicon solar cells was analyzed. Both, n-type cells with non-diffused front surface and p-type cell with floating n-emitter show a pronounced non-linearity due to strong illumination dependence of the passivation quality of the non-diffused surface and the floating junction respectively. Quantum efficiency (QE) of this cell type drops significantly for the illumination lower than 0.5 suns. In contrast the QE of n-type cells with n+-front surface field (FSF) is linear. Low illumination current characteristics of all three of the analyzed structures could be well described by physical models. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

One of the most often mentioned advantages of back-junction back-contacted silicon solar cells is that this cell structure has no shading losses, because metallization fingers and busbars are both located on the rear side of the solar cell. However, this is only true if only optical shading losses are regarded. In this work electrical shading losses due to recombination in the region of base busbar and fingers are analyzed using two-dimensional numerical device and network simulations. The base doping dependence of these effects is investigated as well as the influence of the rear side passivation. The results of the simulations are compared with EQE maps of back-junction solar cells. The influence of the busbars is quantified and the influence on the overall cell performance is discussed.

The role of the phosphorus-doped front surface field (FSF) in n-type back-contact back-junction silicon solar cells was analyzed. The FSF improves the quality of the front surface passivation and enables very high efficiencies even for the cells with higher front surface recombination velocity. The stability of the front surface passivation using the FSF with respect to UV-light was analyzed by measurements of lifetime samples. Application of the FSF significantly improves the UV-light stability. The surface saturation current density (J 0e ) of the textured lifetime samples without FSF increased form 30 fA/cm2 to almost 450 fA/cm2 after 55 hours of UV-light exposure. J 0e of the samples with FSF showed only a marginal increase from 30 to 35 fA/cm2. An additional positive effect of the FSF is the reduction of the lateral resistance losses. These losses are caused by a significant increase of the pitch on the rear cell side, when only low-cost structuring technologies (screen-printing and laser processing) are applied. An experimental study showed that the FSF strongly improved the fill factors of the cells with large pitches. Two-dimensional device simulations revealed that the FSF significantly contributes to the lateral transport of the majority carrier's current. The best cell efficiency of 21.3 % was obtained for the solar cell with a 1 Ω cm specific base resistivity and a front surface field with a sheet resistance of 148 Ω/sq.

We have developed a model to predict and analyze the photocurrent generation and resulting charge carrier Dissociation and Collection Efficiency (DCE) through reflectivity and quantum efficiency spectra. The DCE is regarded as a function of the morphology and exciton transport properties of the bulk heterojunction and is therefore a way to investigate the final properties of photoactive layer in a solar cell. Method proposed allows determination of the efficiency at which photogenerated excitons are dissociated in a working device with respect to the position in the cell at which the generation occurs. The method is tested on our results as well as on a number of results already present in the literature.

In this work, a one-dimensional analytical model to calculate the quantum efficiency in back-junction solar cells with and without a high-low junction on the front side is presented. The analytical model, based on the reciprocity theorem for charge collection, is compared with numerical device simulations taking into account the influence of high-injection effects. Using the analytical model, the influence of base doping concentration and surface recombination velocity on the internal quantum efficiency of a n-type back-junction solar cell is analyzed.