The innovative core-ring structured NiCo 2 O 4 nanoplatelets were found to be novel and promising photocatalysts. The physical and photophysical properties of the photocatalyst were characterized by SEM, TEM, XPS, UV-vis absorption, and photoluminescence, respectively. The core-ring NiCo 2 O 4 nanoplatelets were composed of much smaller nanocrystallines, with an average size of 80-150 nm, compared to the ordinary NiCo 2 O 4 prepared through a conventional hydroxide decomposition method. Moreover, the optical band gap energies of the core-ring NiCo 2 O 4 nanoplatelets were estimated to be 2.06 and 3.63 eV from the UV-vis absorption spectra. The core-ring structured NiCo 2 O 4 photocatalyst exhibited a much higher photocatalytic activity for the degradation of methylene blue than the ordinary NiCo 2 O 4 and TiO 2 under visible light irradiation (>420 nm). This enhanced photocatalytic activity of the core-ring NiCo 2 O 4 nanoplatelets was attributed to their higher optical absorption ability, smaller particle size, and more active internal electron transitions. On the basis of all the results, the band structure of the photocatalyst was discussed.

Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid-base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (Voc) of 0.94 V, a short-circuit current (Jsc) of 20.2 mA cm(-2), a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material.

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Organometal halide perovskite solar cells (PSCs) are nowadays regarded as a rising star in photovoltaics. In particular, PSCs incorporating oriented TiO nanorod (NR) arrays as the electron transport layer (ETL) have attracted significant attention owing to TiO NR's superior electron transport abilities and its potential in long-term stable PSCs. In addition to improve the electron-transport ability of TiO NRs, the tuning of the band alignments between the TiO NR array and the perovskite layer is also crucial for achieving efficient solar cells. This work describes a facile, one-step, solvothermal method for the preparation of tantalum (Ta) doped TiO NR arrays for efficient PSCs. It is shown that the trace doping with Ta tunes the electronic structure of TiO NRs by a synergistic effect involving the lower 5d orbitals of the doped Ta ions and the reduced oxygen vacancies. The synergistic tuning of the electronic structure improves the band alignment at the TiO NR/perovskite interface and boosts the short-circuit current and the fill factor. By using the optimized doped TiO NR array as the ETL, a record efficiency of 19.11% was achieved, which is the highest among one-dimensional-array based PSCs.