Unintentional Hydrogen Incorporation into the SnO₂ Electron Transport Layer by ALD and Its Effect on the Electronic Band Structure

Abstract

This work reports the influence of atomic layer deposition (ALD) using its variants as thermal ALD, remote plasma ALD (RPALD), and direct plasma ALD on the physical parameters of the as-deposited SnO x films. The deposition process and chemical composition are related to their electronic band structure such as valence band maximum, conduction band minimum, band gap, and work function. Oxidant agents such as H 2 O, O 2 , and O 3 were evaluated with deposition temperatures of 80 and 200 °C. Each of the SnO x films were integrated into a solar cell prototype as an electron transport layer, yielding the maximum photovoltaic efficiency of 15.15% for the cell using the SnO x film obtained with oxygen-assisted RPALD at 80 °C. Tin oxides deposited at 200 °C using ozone and oxygen, respectively, feature surface plasmon resonance (SPR) under near-infrared irradiation (0.5 eV), which was detected by reflection electron energy loss and X-ray photoelectron spectroscopies. The unintentionally incorporated substitutional hydrogen acting as a shallow donor is responsible for the SPR effect, defect states in the band gap, and considerably reducing photovoltaic efficiency of the solar cells studied. This doping can be detected by in situ quadrupole mass spectroscopy characterization in the absence of CH 2 among reaction byproducts at the ALD oxidation step.

Elucidating Interfacial Limitations Induced by Tin Oxide Electron Selective Layer Grown by Atomic Layer Deposition in N−I−P Perovskite-Based Solar Cells

“…Hence, both types of films seem to contain a major SnO x phase, with 1.8 ≤ x < 2, which is slightly under-stoichiometric, mixed with oxidized compounds such as −OH species. This result is quite common for SnO 2 thin films deposited at low temperatures, , and these oxygen vacancies are believed to be the origin of the native N-type doping and thus of the electrical conductivity in SnO 2 . ,, …”

“…Hence, both types of films seem to contain a major SnO x phase, with 1.8 ≤ x < 2, which is slightly under-stoichiometric, mixed with oxidized compounds such as −OH species. This result is quite common for SnO 2 thin films deposited at low temperatures, 43,45 and these oxygen vacancies are believed to be the origin of the native N-type doping and thus of the electrical conductivity in SnO 2 . 6,21,46 On this aspect, the slightly lower amount of O in SnO 2 ALD films in comparison to SnO 2 NP films agrees with the strongly reduced electrical resistivity of the former with respect to the reference films.…”

Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28%

“…[16,17] Typically, SnO x layers are typically grown at low temperatures (<120°C) using tetrakis(dimethylamino) tin (TDMA-Sn) and water as the metal-organic precursor and oxidant agents, respectively. [18,19] Although SnO x itself is an effective electron-selective transport material, [20] an additional fullerene layer is deposited before ALD processing. [21][22][23][24] From the perspectives of cost reduction and mechanical-strength improvement, it is desirable to eliminate the need or significantly decrease the thickness of the fullerene layer underneath the SnO x layer.…”