Site-Selective Passivation of Defects in NiO Solar Photocathodes by Targeted Atomic Deposition

Abstract

For nanomaterials, surface chemistry can dictate fundamental material properties, including charge-carrier lifetimes, doping levels, and electrical mobilities. In devices, surface defects are usually the key limiting factor for performance, particularly in solar-energy applications. Here, we develop a strategy to uniformly and selectively passivate defect sites in semiconductor nanomaterials using a vapor-phase process termed targeted atomic deposition (TAD). Because defects often consist of atomic vacancies and dangling bonds with heightened reactivity, we observe-for the widely used p-type cathode nickel oxide-that a volatile precursor such as trimethylaluminum can undergo a kinetically limited selective reaction with these sites. The TAD process eliminates all measurable defects in NiO, leading to a nearly 3-fold improvement in the performance of dye-sensitized solar cells. Our results suggest that TAD could be implemented with a range of vapor-phase precursors and be developed into a general strategy to passivate defects in zero-, one-, and two-dimensional nanomaterials.

Overcoming the Limitations of Sputtered Nickel Oxide for High‐Efficiency and Large‐Area Perovskite Solar Cells

“…It has been confirmed that, as shown in Figure S4A in the Supporting Information, the solar cells with NiO x sputtered using a low oxygen partial pressure have a higher performance than those of the devices with NiO x sputtered using a high oxygen partial pressure. A possible reason is that the presence of excess Ni 3+ in the film sputtered from a high oxygen partial pressure may be responsible for the high rate of recombination, which has also been widely reported in the dye‐sensitized solar cells previously 42, 43, 44. However, further explanation of this improvement is needed, which is out of the scope of this paper.…”

From Bulk to Surface: Sodium Treatment Reduces Recombination at the Nickel Oxide/Perovskite Interface

“…The p‐type conductivity of NiO is associated with the presence of the thermodynamically stable Ni 2+ vacancy, and the consequent stabilization into the crystal lattice of Ni 3+ cations . Ni 3+ states are shallow levels close to the valence band (VB) edge, resulting in a p‐type self‐doping. Ni 2+ substitutional replacement with a monovalent cation induces p‐type doping, enhancing the Ni 3+ state density.…”

Chemical and Physical Reduction of High Valence Ni States in Mesoporous NiO Film for Solar Cell Application

“…18 However, the presence of excess Ni 3+ at the surface of the film may be responsible for the high rate of recombination between the reduced dye and holes in the NiO observed with organic photosensitizers. [19][20][21][22][23][24] Therefore we have attempted to reduce the amount of Ni 3+ in the NiO film. We reduced the amount of Ni 3+ by both a chemical and a thermal method.…”