In Situ Transmission Electron Microscopy Study of Molybdenum Oxide Contacts for Silicon Solar Cells

Ali, Haider; Koul, Surrinder; Gregory, Geoffrey; Bullock, James; Javey, Ali; Kushima, Akihiro; Davis, Kristopher O.

doi:10.1002/pssa.201800998

Cited by 11 publications

(13 citation statements)

References 23 publications

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“…To study a nanomaterial, one way is to fabricate a device on substrate . For example, Ali et al have recently studied molybdenum oxide contacts for crystalline‐Si (c‐Si) photovoltaic device, using an in situ heating holder (Gatan) in TEM . In this research, a combination of transmission line measurements and in situ TEM was used to investigate a molybdenum oxide (MoO x ) and aluminum contact for crystalline silicon solar cells.…”

Section: Energy Conversionmentioning

confidence: 99%

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Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

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replacing gasoline, diesel, or other types of fuels with electricity, it is expected that our world will become more environmentally friendly by storing energy directly from sustainable sources, such as solar, wind, geothermal, bioenergy, and the ocean. Even Australia, as a country with abundant energy resources, has identified energy as one of the key scientific research priorities. It is clear that the efficiency of energy harvesting and consumption must be improved, emissions must be reduced, and the integration of various energy sources into the electricity grid and chemical storage must be implemented. A desirable outlook is one with a variety of energy sources and mechanisms that significantly reduces carbon emissions and is economical for consumers and society. Recent fast-growing research should boost the development of reliable, highly efficient, low-cost, and sustainable energy materials that are effective for new technologies and that satisfy the growing demand for energy storage and climate change solutions.The progress in energy materials is indeed significant, however, as the expectations of energy materials research are always quite high, it is not sufficient. Particularly, the material performances are always theoretically predicted but are limited by the underlying mechanisms in real applications. As a wellknown example, silicon is expected to deliver a high theoretical capacity of 4200 mAh g −1 in the form of Li 4.4 Si, and is thought to replace the currently commercial graphite with a capacity of 372 mAh g −1 . However, in real applications, it is found that Si exhibits more than 360% of volume expansion during lithiation, which leads to battery anode failure. In the last few years, TEM, especially in situ TEM, has provided exceptional advantages in investigating the lithiation process of silicon anodes: direct imaging, full crystallography information, and real-time recording have all become possible. By directly observing the charge/discharge processes of Si anodes, the dynamics of expansion have been well understood. The research has then been focused on structural designs of composites containing Si to overcome the expansion. The Si composites (for instance, carbon-wrapped Si nanoparticles with different sizes) were directly analyzed by in situ TEM to determine the best structural design. [12] From 2012, in situ TEM became an essential tool to review and evaluate structural designs for high-capacity anodes with significant volume expansions. The same scenarios apply to similar research topics. In situ transmission electron microscopy (TEM) is one of the most powerfulapproaches for revealing physical and chemical process dynamics at atomic resolutions. The most recent developments for in situ TEM techniques are summarized; in particular, how they enable visualization of various events, measure properties, and solve problems in the field of energy by revealing detailed mechanisms at the nanoscale. Related applications include rechargeable batteries such as Li-ion, Na-ion, Li-O 2 , Na-O 2 , Li...

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Section: Energy Conversionmentioning

confidence: 99%

“…In addition, oxygen diffusion takes place at the MoO x /Al interface of MoO x /Al leading to the creation of an interlayer of aluminum oxide of ≈2–3 nm thick. These authors noted that the MoO x /Al contact is rather stable after heating up to 200 °C and maintains the Ohmic contact with sufficiently low resistivity …”

Section: Energy Conversionmentioning

confidence: 99%

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

et al. 2019

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“…Previous experiments have shown that when Al is deposited directly onto MoO x , O tends to migrate toward the Al interface and form a thin Al 2 O 3 interlayer. [46] It is evident that no interfacial oxide layer exists at the Ni/MoO x interface.…”

Section: Ultraviolet Photoelectron Spectroscopy Characterizationmentioning

confidence: 99%

Spatial Atomic Layer Deposition of Molybdenum Oxide for Industrial Solar Cells

Gregory

Luderer

Ali

et al. 2020

Adv Materials Inter

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alignment for charge transport. [11] TMOs have work functions ranging from 3 (ZrO 2) to 7 eV (V 2 O 5), making them suitable candidates for energy-level alignment in a variety of devices. [12] In crystalline silicon (c-Si) solar cells, TMOs are being used as transparent, dopant-free heterocontacts to the silicon absorber. [13] These have the potential to replace the heavily doped contacts found in current state-of-the-art heterojunction solar cells, [14,15] which can suffer from parasitic optical absorption and increased Auger recombination at the silicon surface. [16,17] TMOs are commonly deposited using different physical vapor deposition (PVD) techniques such as thermal evaporation and sputtering. [18,19] Atomic layer deposition (ALD) has emerged as an alternative for TMO deposition. [20] ALD offers greater thickness control and uniformity than PVD due to its reaction-limited growth process, making it ideal for applications requiring ultra-thin, conformal oxides on textured silicon surfaces. [21-24] While this technique has many advantages over PVD, depending on molecular precursor choice, it may require "energy enhancement" of the oxidant pulse, most commonly in the form of plasma or ozone, to achieve efficient growth. [25] Additionally, the growth rate of ALD is typically on the order of angstroms per Molybdenum oxide thin films are successfully deposited using spatial atomic layer deposition (SALD), a tool designed for high-throughput industrial film growth. The structural and optical properties of the film are evaluated using ultraviolet photoelectron spectroscopy, high-resolution transmission electron microscopy, and spectroscopic ellipsometry. To demonstrate the applicability of molybdenum oxide in industrial settings the films are applied as holeselective silicon heterojunction contacts for solar cells. When paired with intrinsic amorphous silicon passivation layers, implied open-circuit voltages of 699 mV are achieved. The carrier transport is unaffected by low-temperature contact anneals up to 300 °C with contact resistivities of ≈ 10 mΩ cm 2. Finally, the optical performance of silicon solar cells featuring different front hole-selective heterojunction structures are simulated. It is shown that the generation current density of heterojunction solar cells can be significantly increased with the addition of SALD molybdenum oxide contacts.

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“…Additionally, several groups 49–52 report the formation of a relatively thick 2‐ to 3‐nm sub‐stoichiometric silicon oxide (SiO 2 ) interlayer at the (i)a‐Si:H/MoO x interface in the as‐deposited state. More controversial is the instance of MoO x in stack with (i)a‐Si:H or indium tin oxide (ITO).…”

Section: Introductionmentioning

confidence: 99%

Strategy to mitigate the dipole interfacial states in (i)a‐Si:H/MoO_x passivating contacts solar cells

Mazzarella

Alcañiz

Procel

et al. 2020

Progress in Photovoltaics

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Molybdenum oxide (MoOx) is attractive for applications as hole‐selective contact in silicon heterojunction solar cells for its transparency and relatively high work function. However, the integration of MoOx stacked on intrinsic amorphous silicon (i)a‐Si:H layer usually exhibits some issues that are still not fully solved resulting in degradation of electrical properties. Here, we propose a novel approach to enhance the electrical properties of (i)a‐Si:H/MoOx contact. We manipulate the (i)a‐Si:H interface via plasma treatment (PT) before MoOx deposition minimizing the electrical degradation without harming the optical response. Furthermore, by applying the optimized PT, we can reduce the MoOx thickness down to 3.5 nm with both open‐circuit voltage and fill factor improvements. Our findings suggest that the PT mitigates the decrease of the effective work function of the MoOx (WFMoOx) thin layer when deposited on (i)a‐Si:H. To support our hypothesis, we carry out electrical simulations inserting a dipole at the (i)a‐Si:H/MoOx interface accounting the attenuation of WFMoOx caused by both MoOx thickness and dipole. Our calculations confirm the experimental trends and thus provide deep insight in critical transport issues. Temperature‐dependent J‐V measurements demonstrate that the use of PT improves the energy alignment for an efficient hole transport.

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In Situ Transmission Electron Microscopy Study of Molybdenum Oxide Contacts for Silicon Solar Cells

Cited by 11 publications

References 23 publications

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

Spatial Atomic Layer Deposition of Molybdenum Oxide for Industrial Solar Cells

Strategy to mitigate the dipole interfacial states in (i)a‐Si:H/MoO_x passivating contacts solar cells

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In Situ Transmission Electron Microscopy Study of Molybdenum Oxide Contacts for Silicon Solar Cells

Cited by 11 publications

References 23 publications

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

Recent Progress of In Situ Transmission Electron Microscopy for Energy Materials

Spatial Atomic Layer Deposition of Molybdenum Oxide for Industrial Solar Cells

Strategy to mitigate the dipole interfacial states in (i)a‐Si:H/MoOx passivating contacts solar cells

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Strategy to mitigate the dipole interfacial states in (i)a‐Si:H/MoO_x passivating contacts solar cells