Spatial Atomic Layer Deposition of Molybdenum Oxide for Industrial Solar Cells

Abstract

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.

Atomic layer deposition of vanadium oxide films for crystalline silicon solar cells

“…In this novel work Yang et al investigates the possibilities of this technique for Vanadium oxide using it in combination with an amorphous silicon passivating buffer, obtaining outstanding devices up to 21.6% efficiencies. Other attempts to fabricate operative photovoltaic devices with ALD deposited TMOs have not been as successful 35,36 indicating how ALD deposition of Transition Metal Oxides is not an easy task. The explored solar cell architecture by Yang et al does not take advantage of the reported TMO enhancement in optical properties with respect to the conventional heterojunction structure using amorphous silicon 26 .…”

High‐Throughput Atomic Layer Deposition of P‐Type SnO Thin Film Transistors Using Tin(II)bis(tert‐amyloxide)

“…Transparent semiconducting metal-oxides have become the foundation of devices such as thin-film transistors (TFTs), solar cells, photodetectors, and memories. [1][2][3][4] The majority of these devices rely on n-type semiconducting compounds (e.g., InGaZnO, InZnO, ZnSnO, and ZnO), for which materials and processes are well established. In contrast, the development of reliable and high performance p-type oxide materials has proven itself to be challenging owing to their inherently high density of interfacial defect states and comparably poor electrical performance, [5] which in turn hampers the effective spatial separation of precursor and coreactant, i.e., the substrate moves underneath injector heads from which either precursor or coreactant are continuously flowing.…”

Recent Advances in Materials Design Using Atomic Layer Deposition for Energy Applications

“…[ 256 ] In recent times, SALD has also been employed to deposit materials for various applications such as ZnO in thin film Li‐ion batteries, [ 257 ] SnO x in perovskite solar cell, [ 258 ] Al 2 O 3 as moisture barrier coating, [ 259 ] and MoO x as charge selective layer in Si solar cell. [ 260 ] Similarly, close‐proximity SALD has been employed commercially by companies such as Levitech and SoLayTec to deposit Al 2 O 3 thin films on Si solar cells for surface passivation. To date, high throughput SALD have mainly been limited to few materials such as ZnO, Al 2 O 3 , TiO 2 .…”