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Minimizing transport losses in novel solar cell concepts is often linked to improvements at the transparent conductive oxide (TCO)/doped silicon contact. A detailed understanding of the determining factors for an efficient transport at this heterojunction is essential, such as work function matching and efficient tunneling transport. In this article, we analyze the different TCO contact parameters experimentally and by numerical device simulations. We show that work function matching by using a proper interlayer [e.g., tungsten oxide (WO x )] can be an effective means to improve the fill factor of silicon heterojunction solar cells. However, we showcase that an improved work function matching achieved by changing the doping of a TCO interlayer can be superimposed by a less efficient tunneling transport, for e.g., due to an interfacial oxide. Furthermore, we show that for n-tunnel oxide passivating contacts, an unintentionally grown oxide at the TCO/poly-Si contact could be a possible explanation for recently observed transport losses.

This work addresses general aspects of the front side TCO and grid electrode for application in a Perovskite-Silicon tandem device by optical and electrical modelling. We highlight the need to optimize the front electrode for the tandem case, where in contrast to silicon single junction devices, there is (i) about half the current, which significantly reduces resistive losses in the front electrode, (ii) a lower refractive index of the absorber (most Perovskites at 600 nm:~2.4 vs. Si: ~4.2), (iii) almost no lateral transport in the perovskite top cell, and (iv) a lower thermal device stability (~100-130°C vs. 200°C), which results in less efficient sintering of the Ag pastes and hence higher metal grid resistivity. This study concludes that compared to silicon heterojunction cells (SHJ), the thickness of the front side TCO electrode should be reduced from 75 nm to 20 nm. For the grid electrode, the low-temperature Ag pastes results in higher line resistivities and curing durations. Furthermore, we showcase that for the multi-wire interconnection concept, the number of wires can be significantly reduced from 18 wires to less than 9 depending on the front metallization.

Transparent conducting oxides (TCOs) used in solar cells must be optimized to achieve minimum parasitic absorption losses while providing sufficient lateral conductivity. Low contact resistance with the adjacent device layers and low damage to the substrate during deposition of the TCO are also important requirements to ensure high solar cell efficiencies. Pulsed laser deposition (PLD) has been proposed as an alternative low-damage TCO deposition technique on top of sensitive layers and interfaces in organic and perovskite solar cells but is yet to be studied for the more mature silicon technology. Focusing on the PLD deposition pressure as the key parameter to reduce damage, we developed tin-doped indium oxide (ITO) with a sheet resistance of 60 ω □-1 at different pressures and implemented it in silicon heterojunction (SHJ) solar cells. Buffer-free semi-transparent perovskite cells with the same PLD ITO electrodes were also fabricated for comparison. While in the perovskite cells increased ITO deposition pressure leads to an improved open circuit voltage and fill factor indicative of damage reduction, SHJ cells with PLD ITO at all conditions maintained a high passivation quality, but increased pressures lead to high series resistance. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry confirmed the formation of a parasitic SiOx at the ITO/a-Si:H interface of the SHJ cell causing a transport barrier. The optimized ITO films with the highest carrier density were able to obtain >21% SHJ efficiency with 75 nm-thick PLD ITO. Moreover, reducing the ITO thickness to ∼45 nm and using TiOx for optical compensation enables fabrication of SHJ devices with reduced indium consumption and efficiencies of >22%. This journal is

Perovskite silicon tandem solar cells have the potential to overcome the efficiency limit of single-junction solar cells. For both monolithic and mechanically stacked tandem devices, a semi-transparent perovskite top solar cell, including a transparent contact, is required. Usually, this contact consists of a metal oxide buffer layer and a sputtered transparent conductive oxide. In this work, semi-transparent perovskite solar cells in the regular n-i-p structure are presented with tin-doped indium oxide (ITO) directly sputtered on the hole conducting material Spiro-OMeTAD. ITO process parameters such as sputter power, temperature, and pressure in the chamber are systematically varied. While a low temperature of 50 °C is crucial for good device performance, a low sputter power has only a slight effect, and an increased chamber pressure has no influence on device performance. For the 5 × 5 mm2 perovskite cell with a planar front side, a 105 nm thick ITO layer with a sheet resistance of 44 Ω sq-1 allowing for the omission of grid fingers and a MgF2 antireflection coating are used to improve transmission into the solar cells. The best device achieved an efficiency of 14.8%, which would result in 24.2% in a four-terminal tandem configuration.

In this article, the development and optimization of carrier-selective and passivating contacts by industry-scale inline plasma-enhanced chemical vapor deposition and their successful integration into solar cells are reported. Amorphous Si thin films with varying carbon content (SiC x ) were deposited on a thermally grown ultrathin tunnel oxide (TOPCon) and electrically characterized. Furthermore, the impact of a vacuum break (VB) during the deposition of a layer stack consisting of intrinsic amorphous Si [a-Si:H(i)] and boron-doped SiC x was investigated. That is, samples that were processed with VB were exposed to ambient air, and hence, a thin native oxide was formed on the a-Si:H(i) layer, which affected the boron diffusion into the absorber resulting in a distinct anneal behavior of the contacts. Upon optimization, these layers provided an excellent surface passivation quality, which was reflected in an implied open-circuit voltage of 733 mV for n-type and 716 mV for p-type TOPCon structures, respectively. In addition, very low contact resistivities of 0.3 mO⋅cm² for n-type and 0.5 mO⋅cm² for p-type TOPCon were measured, respectively. These optimized TOPCon structures were implemented into both sides contacted p-type laboratory solar cells. After a two-step furnace anneal, these cells achieved a maximum energy conversion efficiency of 22.7% with evaporated contacts.

Resistive losses in silicon heterojunction (SHJ) solar cells are partly linked to transport barriers at the amorphous silicon/crystalline silicon (a-Si:H/c-Si) and transparent conductive oxide (TCO)/a-Si:H interfaces. A key parameter is the position of the Fermi-level on either side of the junction which we modify by a systematic doping variation of the amorphous silicon and the transparent conductive oxide. We identify the charge carrier concentration to be the main driver for low contact resistance. For a-Si:H, this is achieved by using a sufficient but not too high doping gas concentration during deposition. For indium tin oxide (ITO) and aluminum zinc oxide (AZO), no or only a very low oxygen (O 2 ) gas concentration during deposition is needed. We show that a stack of low-oxygen ITO interlayer and an oxygen-rich ITO ""bulk"" layer is not only an effective means to combine efficient transport and low TCO absorption but also to improve the thermal stability of the a-Si:H/TCO/metal contact resistivity ( rc ). Such a layer stack helps to relax the constraints regarding the optoelectrical performance and improves the efficiency of SHJ solar cells.

In recent years, the incorporation of hydrogen into indium and zinc oxide based TCOs has been recognized as an effective technique to improve the charge carrier mobility and hereby to relax the transparency-conductivity tradeoff within thethin films. On the other hand, the process sequence of poly-Si/SiOx based contacts typically requires an extra rehydrogenation stepin order to improve the chemical interface passivation. This article addresses the combination of the two matters by studying the ability of both atomic layer deposited and sputter-deposited TCOs to serve as hydrogenation sources. Here, we demonstrate improved passivation of poly-Si(n)/SiOx contacts subsequent to TCO coatings and postdeposition thermal treatments resulting in iVoc values of up to 743 and 730 mV for planar and random pyramid textured surfaces, respectively. Thus, a high passivation quality could be obtained without the need of additional hydrogenation treatments.For the textured interfacemorphology, a substantial hydrogen flux toward the SiOx region turned out to be essential. This could either be ensured by adjusting the hydrogen partial pressure during the TCOgrowth process or by the addition of a thinAlOx layer, serving as a effusion barrier.

Perovskite silicon tandem solar cells can exceed the efficiency limit of 29.4% of single junction silicon solar cells, with comparably low additional costs for depositing the layers for the perovskite solar cell. Hence, they are an attractive option to further decrease the costs of photovoltaic electricity generation. We present, how by optimizing perovskite absorber composition, choosing adequate carrier selective contact layers, introducing surface passivation and optimizing the individual layer thicknesses solar cell efficiencies above 25% can be realized experimentally. Furthermore, we discuss different options for reducing front surface reflection by anti-reflection coatings, structured foils and deposition on textured silicon wafers and their impact both on solar cell efficiency as well as on the yearly energy yield. Deposition on textured silicon wafers promises highest energy yield. Hence, we show how perovskite absorbers can be deposited on such substrates by either co-evaporation or hybrid processing combining evaporation and subsequent wet-chemical processing. By bottom up cost calculations we finally show how and under which conditions perovskite silicon tandem solar cells can yield an economic advantage.

The capability for contact formation on indium tin oxide layers of different low-temperature screen printing silver pastes after thermal curing and photonic sintering is evaluated in detail. The 80-nm-thick indium tin oxide layers used in this study are sputtered at three different oxygen gas flows and, consequently, differ by their electrical and optical properties. All pastes are analyzed by means of simultaneous thermogravimetry-differential scanning calorimetry. After printing and contact formation processing, the lateral resistivity of the metal contacts and their contact resistivity to the indium tin oxide layers are determined. Furthermore, the microstructure of the metal electrodes is investigated to gain a deeper understanding of the underlying contact formation mechanisms. Besides low-temperature curing at T curing, low = 180–220 °C, as conventionally applied to silicon heterojunction solar cells, photonic sintering and thermal curing at medium temperatures T curing, mid = 250–350 °C are utilized. The higher curing temperatures in the range of T curing, mid enhance the sintering and densification processes of the different pastes, and thereby, lateral resistivities of 2.4–3.5 μΩ⋅cm and contact resistivities of 1.0–2.5 mΩ⋅cm2 are achieved. The results indicate a promising industry-relevant non-firing-through metallization approach for, e.g., poly-silicon-based structures like tunnel oxide passivating contacts, which allow comparatively high temperatures for contact formation processing. With thermal curing at T curing, low and photonic sintering, both compatible with temperature-sensitive silicon heterojunction solar cells, lateral finger resistivities of 6.5–9.4 μΩ⋅cm and contact resistivities of 1.2–2.5 mΩ⋅cm2 are achieved. Thereby, photonic sintering has the potential of a significantly reduced process time from several minutes down to 1–4 ms.

Intense pulsed light (IPL) is capable of entirely replacing thermal annealing (curing and contact formation) within back end processing of silicon solar cells with passivating contacts. In order to demonstrate this, full-size silicon heterojunction (SHJ) cells with IPL-processed screen-printed metal contacts are fabricated. The device with the highest conversion efficiency reaches 23.0%, which is confirmed by Fraunhofer ISE CalLab. On average, IPL-annealed SHJ cells outperform their thermally treated pendants by 0.3–0.4%abs, in particular due to higher open-circuit voltages and fill factors. To further exploit the potential of IPL, it is applied to tunnel oxide passivating contacts (TOPCon). 2 cm × 2 cm-sized p-type solar cells with TOPCon layers on both sides are fabricated. On the front they exhibit indium tin oxide (ITO) layers as well as screen-printed metal contacts which are either thermally or IPL-annealed. The trade-off between low contact resistivity at the TOPCon/ITO interface and high-quality surface passivation (open-circuit voltages of up to 709.4 mV) is balanced, which is a current challenge for the optimization of such devices. The IPL-processed cells’ series resistances do not differ significantly from those of thermally treated ones. Due to the pulse durations of several milliseconds only, IPL is very fast and offers a high throughput and, therefore, cost saving potential.

We report on the development of the TOPCon technology on large area focusing on the deposition technology for the a-SiC x (n) layer and the rear side metallization. We demonstrate that kHz direct-plasma technology can be used to deposit the a-SiC x (n) layers and that concerns about ion bombardment damaging the thin SiO x are not justified. Excellent surface passivation quality was achieved with lifetimes up to 13 ms ($1 \Omega \mathbf{cm} n$-type). The layers can be contacted using ITO reaching specific contact resistivities in the range of 5 m$\Omega \mathbf{cm} ^{\mathbf{2}}$. Solar cells with a boron diffused emitter and TOPCon rear are presented resulting in an efficiency of 23.4 % with laser contact opening and NiCuAg plating.

This work addresses the development of a transparent conductive oxide (TCO)/metal stack for n-type Si solar cells featuring a tunnel oxide passivating rear contact (TOPCon). While poly-Si based passivating contacts contacted by local fire-through metallization currently show an increased recombination at the metal contacts and a poor infrared (IR) response, we aim to realize a full-area metallization which maintains the high level of surface passivation and avoids IR losses. Some research groups have reported that sputtering TCOs on poly-Si based passivating contacts degrades the surface passivation and unlike the SHJ cells this degradation cannot be cured completely at Tcure ∼ 200°C. However, the higher thermal stability of TOPCon allows for higher Tcure of up to 400°C, which can effectively restore the surface passivation. On the other hand, the contact resistivity (ρc) of the TOPCon/ITO/metal contact increased by several orders of magnitude in our test structures during annealing at such high temperatures. Possible reasons like the formation of an interfacial oxide are currently under investigation. Increasing the poly-Si thickness and/or doping mitigated the effect of sputter damage, but this will come at the cost of more parasitic absorption. However, by adapting the sputter and the subsequent annealing process, we were able to realize low damage deposition of ITO (loss in implied Voc ∼ 7 mV) on thin, lowly doped poly-Si layers on textured wafers, yielding reasonable contact properties (ρc ∼ 40 mΩcm2; of the whole rear contact stack).This work addresses the development of a transparent conductive oxide (TCO)/metal stack for n-type Si solar cells featuring a tunnel oxide passivating rear contact (TOPCon). While poly-Si based passivating contacts contacted by local fire-through metallization currently show an increased recombination at the metal contacts and a poor infrared (IR) response, we aim to realize a full-area metallization which maintains the high level of surface passivation and avoids IR losses. Some research groups have reported that sputtering TCOs on poly-Si based passivating contacts degrades the surface passivation and unlike the SHJ cells this degradation cannot be cured completely at Tcure ∼ 200°C. However, the higher thermal stability of TOPCon allows for higher Tcure of up to 400°C, which can effectively restore the surface passivation. On the other hand, the contact resistivity (ρc) of the TOPCon/ITO/metal contact increased by several orders of magnitude in our test structures during annealing at such high temperatu...

Passivating contacts are considered as a possibility to enhance silicon based PV performance due to lower interface recombination rates of charge carriers. Most of the investigation on metal oxide based contacts so far was done in laboratory scale. Mass production requires the scale-up of the processes. This contribution reports on first deposition experiments of MoOx hole selective contacts by industrial size reactive magnetron sputtering and thermal evaporation. Reactive sputtering was carried out on a vertical inline tool equipped with a rotatable target of 1 m length. Thermal evaporation was conducted with a linear evaporation source of 46 cm length. Films were deposited on solar cell precursors in order to estimate charge carrier selectivity and band bending induced into the c-Si wafer by the MoOx based hole contact. First results show that the selectivity, band bending, and optical transmission of reactively sputtered MoOx films depend on the working point of the reactive sputter process. However, the selectivity still is far from what was reached in small-scale evaporation experiments. Films deposited with the industrial linear evaporation source show much better selective properties even comparable to lab-scale evaporation. Based on these results there seems to be a high potential to transfer the small scale laboratory evaporation process to larger areas in dynamic deposition, but further work is needed to tailor the properties of the sputter deposited MoOx.

This work addresses the development of transparent conductive oxides (TCOs) for Si solar cells featuring SiOx/poly-Si based passivating contacts. Minimizing the thickness of the parasitically absorbing poly-Si layer is essential to reduce losses in the generation of current. However, as the poly-Si shields the critical absorber surface region during the sputter process of an overlying TCO film, the degradation in passivation quality is more severe for poly-Si films below 20 nm. For a thermal annealing of this sputter damage, a trade-off between improved surface passivation and the formation of a transport barrier exists, which needs to be considered for contact engineering. By adjusting the DC sputter process and the subsequent curing procedure, effective passivation recovery of textured samples featuring ultrathin (

The chiral magnet Cu$_{2}$OSeO$_{3}$ hosts a skyrmion lattice, that may be equivalently described as a superposition of plane waves or lattice of particle-like topological objects. A thermal gradient may break up the skyrmion lattice and induce rotating domains raising the question which of these scenarios better describes the violent dynamics at the domain boundaries. Here we show that in an inhomogeneous temperature gradient caused by illumination in a Lorentz Transmission Electron Microscope different parts of the skyrmion lattice can be set into motion with different angular velocities. Tracking the time dependence we show that the constant rearrangement of domain walls is governed by dynamic 5-7 defects arranging into lines. An analysis of the associated defect density is described by Frank's equation and agrees well with classical 2D-Monte Carlo simulations. Fluctuations of boundaries show surge-like rearrangement of skyrmion clusters driven by defect rearrangement consistent with simulations treating skyrmions as point particles. Our findings underline the particle character of the skyrmion., Comment: 6 pages, 4 figures, 6 supplement pages, 5 supplemental figures