Nickel oxide (NiO x ) has exhibited great potential as an inorganic hole transport layer (HTL) in perovskite solar cells (PSCs) due to its wide optical bandgap and superior stability. In this study, we have modulated the Ni 2+ vacancies in NiO x film by controlling deposition temperature in a hot-casting process, resulting the change of coordination structure and charge state of NiO x . Moreover, the change of the HOMO level of NiO x makes it more compatible with perovskite to decrease energy losses and enhance hole carrier injection efficiency . Besides, the defect modulation in the electronic structure of NiO x is beneficial for increasing the electrical conductivity and mobility, which are considered to achieve the balance of charge carrier transport and avoid charge accumulation at the interface between perovskite and HTL effectively. Both experimental analyses and theoretical calculations reveal the increase of nickel vacancy defects change the electronic structure of NiO x by increasing the ratio of Ni 3+ /Ni 2+ and improving the p-type characteristics. Accordingly, an optimal deposition temperature at 120 °C enabled a 36.24% improvement in the power conversion efficiency compared to that deposited at room temperature (25 °C). Therefore, this work provides a facile method to manipulate the electronic structure of NiO x to improve the charge carrier transport and photovoltaic performance of related PSCs.
In this work, pure NiO, Al-doped NiO, W-doped NiO and a series of Al/W co-doped NiO nanoflowers were successfully prepared through a simple solvothermal method . Various characterization methods, such as XRD , SEM, TEM, HRTEM and XPS , were used to confirm the physical and chemical properties of the sensitive materials in terms of micro-nano structures, compositions and elemental distributions. The as-obtained Al/W co-doped NiO showed a nanoflower structure with an approximate size of ∼ 200 nm. What's more, among six sensors constructed from the sensitive materials, the sensor based on 3 at% Al 3+ /3 at% W 6+ co-doped NiO (3Al3W-NiO) achieved the highest response (R g /R a =112) toward 100 ppm triethylamine with a low detection limit (1 ppm) at 325 ℃. Besides, this sensor also exhibited excellent response/recovery characteristics and long-term stability. These favorable sensing performances of the 3Al/3 W co-doped NiO sensor are not only modulated by the initial resistance (R a ), but are also closely related to the large specific surface area , porous structures , low crystallinity , rich oxygen vacancies and high Ni 3+ /Ni 2+ ratio in the composite nanomaterials.
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