Microplasma-synthesized ultra-small NiO nanocrystals, a ubiquitous hole transport material

Abstract

We report on a one-step hybrid atmospheric pressure plasma-liquid synthesis of ultra-small NiO nanocrystals (2 nm mean diameter), which exhibit strong quantum confinement and excellent compatibility as hole transport layer for various solar absorber layers.

Unusual Hole Transfer Dynamics of the NiO Layer in Methylammonium Lead Tri-iodide Absorber Solar Cells

“…From our time-resolved spectroscopic and electrical measurements, we suggest that VB sharing of NiO-MAPI and backward hole injection occurred, as shown in the schematic illustration of Figure . The VB energy levels of MAPI and NiO were almost identical and could perform as an adequate HTL. ,,,,, The increase in the PL intensity with the NiO HTLs could be simply explained by holes having elongated lifetimes. Hole lifetimes of nearly 100 ns were experimentally revealed by a three-component exponential decay model in the trPL, the GSB recovery, and the hole carrier PA decay in TAS (Tables S2,3).…”

“…However, inherent thermal instability, high cost, and incompatible processes became critical problems in PSCs. Therefore, inorganic HTLs such as CuO x , MoO x , CoO x , CuCrO x , and NiO x , have been investigated to overcome these shortcomings. − Although many metal oxides are restricted by their insulating properties, NiO HTLs in PSCs are being continuously studied due to their high PCE and stability. − NiO HTLs have shown many advantages such as valence band (VB) matching with most perovskite absorbers, excellent electron blocking, high transparency, and thermal stability. ,, PSCs with NiO as HTLs have been prepared by various synthesis methods such as solution processsing, , sol–gel methods, , electrodeposition, sputtering, , physical laser deposition (PLD), and atomic layer deposition (ALD). , In addition, as postprocesses, two step annealing and reduced graphene oxide (rGO) incorporation have been tried to improve the intrinsic high resistivity of NiO and its hole transfer characteristics. Furthermore, many studies reported the PCE enhancement by increasing the NiO layers’ conductivity by various metal doping, e.g., Zn, Cu, Co, Ag, and Eu. − However, when one considers NiO is a highly stable wide-bandgap semiconductor and it is difficult to generate defect states at low temperature, it proves that Ni 3+ defect states or doped metal states by simple X-ray photoelectron spectroscopy (XPS) peak deconvolution require further detailed study.…”

“…7−10 NiO HTLs have shown many advantages such as valence band (VB) matching with most perovskite absorbers, excellent electron blocking, high transparency, and thermal stability. 6,8,11 PSCs with NiO as HTLs have been prepared by various synthesis methods such as solution processsing, 9,11 sol−gel methods, 8,12 electrodeposition, 13 sputtering, 14,15 physical laser deposition (PLD), 16 and atomic layer deposition (ALD). 6,17 In addition, as postprocesses, two step annealing 12 and reduced graphene oxide (rGO) incorporation 8 have been tried to improve the intrinsic high resistivity of NiO and its hole transfer characteristics.…”

“…44 Closely positioned VB energy levels of MAPI and p-NiO have been reported many times. 6,8,9,13,16,26 Photogenerated holes in MAPI first transfer to the NiO HTL and are injected backward to MAPI when the hole concentration is high enough in the NiO HTL. Backward hole injection clearly explains the photovoltaic performances of NiO HTLs, such as the increased PL intensity and charge carrier lifetime.…”

Poly(3‐hexylthiophene) stabilized ultrafine nickel oxide nanoparticles as superior electrocatalyst for oxygen evolution reaction: Catalyst design through synergistic combination of π‐conjugated polymers and metal‐based nanoparticles

“…For P3HT to precursor molar ratios of 1.25:1 and 1.5:1 (Figure 1a,c), the interplanar d-spacing measured from the lattice fringe pattern is 0.21 nm, which is consistent with (200) plane of NiO (Figure 1b,d). 52,53 Moreover, on decreasing the amount of P3HT with P3HT to precursor molar ratios of 0.75:1 and 0.5:1, the obtained NPs were found to display an interplanar spacing of 0.24 nm corresponding to the (111) plane of NiO (Figure 1g,h,i,j). 54,55 These optimization suggests that P3HT to precursor molar ratio of 1:1 results in better dispersed NPs compared to a slightly increased or decreased amount of P3HT stabilizing agent.…”