Amorphous Gallium oxide (Ga2O3) thin films were grown by plasma-enhanced atomic layer deposition using O2 plasma as reactant and trimethylgallium as a gallium source. The growth rate of the Ga2O3 films was about 0.6 Å/cycle and was acquired at a temperature ranging from 80 to 250 °C. The investigation of transmittance and the adsorption edge of Ga2O3 films prepared on sapphire substrates showed that the band gap energy gradually decreases from 5.04 to 4.76 eV with the increasing temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that all the Ga2O3 thin films showed a good stoichiometric ratio, and the atomic ratio of Ga/O was close to 0.7. According to XPS analysis, the proportion of Ga3+ and lattice oxygen increases with the increase in temperature resulting in denser films. By analyzing the film density from X-ray reflectivity and by a refractive index curve, it was found that the higher temperature, the denser the film. Atomic force microscopic analysis showed that the surface roughness values increased from 0.091 to 0.187 nm with the increasing substrate temperature. X-ray diffraction and transmission electron microscopy investigation showed that Ga2O3 films grown at temperatures from 80 to 200 °C were amorphous, and the Ga2O3 film grown at 250 °C was slightly crystalline with some nanocrystalline structures.
Albeit considerable attention to the fast‐developing organic thermoelectric (OTE) materials due to their flexibility and non‐toxic features, it is still challenging to design an OTE polymer with superior thermoelectric properties. In this work, two “isomorphic” donor–acceptor (D–A) conjugated polymers are studied as the semiconductor in OTE devices, revealing for the first time the internal mechanism of regioregularity on thermoelectric performances in D–A type polymers. A higher molecular structure regularity can lead to higher crystalline order and mobility, higher doping efficiency, order of energy state, and thermoelectric (TE) performance. As a result, the regioregular P2F exhibits a maximum power factor (PF) of up to 113.27 µW m−1 K−2, more than three times that of the regiorandom PRF (35.35 µW m−1 K−2). However, the regular backbone also implies lower miscibility with a dopant, negatively affecting TE performance. Therefore, the trade‐off between doping efficiency and miscibility plays a vital role in OTE materials, and this work sheds light on the molecular design strategy of OTE polymers with state‐of‐the‐art performances.
Nickel oxide (NiO) has recently attracted great attention for its use as a hole transport layer (HTL) of inverted perovskite solar cells (PSCs). In this paper, NiO films are fabricated on a silicon wafer and fluorine-doped tin oxide by plasma-enhanced atomic layer deposition (PEALD) with nickelocene as the metal precursor and oxygen plasma as the coreactant. The effects of the annealing treatment on the film properties at different annealing temperatures are analyzed. The experimental results show that the PEALD-NiO films have a high thickness uniformity and low surface roughness as evaluated by atomic force microscopy measurements. All the PEALD-NiO films have a wide bandgap and high transmittance of ∼80%–85% in the visible light range. The postannealing treatment induces a reduced electrical resistivity owing to crystal structure repair and surface defect reduction. This treatment also leads to a significantly enhanced wettability of the NiO films, facilitating perovskite layer deposition in subsequent device fabrication. Finally, the inverted PSCs based on the NiO HTL with different annealing temperatures demonstrate an enhanced performance of the device as compared to that with unannealed NiO HTL. The 400 °C-annealed PEALD-NiO HTL yields the best cell conversion efficiency, improving from 15.38% for unannealed NiO to 17.31%, demonstrating the potential of PEALD-NiO compact films for applications in inverted PSCs.
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