Organometal trihalide perovskite solar cells (PSCs) with carbon counter electrode (CE) have attracted tremendous interest due to their remarkable properties such as low cost and high stability. However, carbon-based PSCs always suffer from much lower power conversion efficiency (PCE) than the counterparts with noble metal cathode. Herein, we demonstrate a carbon-based planar heterojunction PSC using high-crystallinity Ni-doped rutile TiO 2 as electron transport layer (ETL) for the first time, while copper phthalocyanine (CuPc) is introduced as hole transport layer (HTL). It is found that Ni doping can shift the Fermi level of the ETL upward and increase the charge mobility of the TiO 2 film, thus enhancing the charge transport and extraction. An optimized PCE of 17.46% was obtained after 0.01 M Ni doping, comparable to or even better than devices with state-of-the-art doped Spiro-OMeTAD as HTL and Au as CE. To the best of our knowledge, this is the highest efficiency that has been reported for carbon-based PSCs. By contrast, the pristine TiO 2 -based device only displayed a PCE of 15.82%. Detailed superior capability of Ni-doped TiO 2 in facilitating charge transfer and suppressing carrier recombination are revealed by Hall effect and photoluminescence (PL) as well as electrochemical impedance spectroscopy (EIS) measurements. Furthermore, the use of highly stable CuPc and commercial carbon makes as-prepared PSCs exhibit excellent stability with no obvious decline in PCE after being stored in ambient air for 1200 h. This work presents an important step forwards to the commercialization of carbon-based PSCs with high efficiency and long-term stability.
Direct conversion of CH 4 to high valued chemicals under mild conditions is attractive but full of challenges. Here, we present a ternary composite that consists of Ni-doped TiO 2 nanocubes (NCs) and CNTs as a new kind of catalyst (denoted as CNTs-Ni@TiO 2 NCs) for CH 4 photocatalytic conversion to C1 oxygenated products at 30 °C. Using H 2 O 2 as an oxidant, a high C1 oxygenated products yield and selectivity of 1.43 mol/(mol Ni ·h) and 95.6% can be reached in 2 h at 30 °C. The superior photocatalytic performance resulted from the synergistic effects of TiO 2 NCs, Ni species, and CNTs such as enhanced visible light absorption , improved electron/hole separation and charge transfer property, and lowered C-H bond cleavage energy required for CH 4 activation, were carefully studied. Good reusability of the catalyst was studied by recycle experiments. Possible reaction mechanism based on the radical routes were carefully discussed by combining in-situ Fourier transform infrared spectroscopy , X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, radical scavenger experiments and density functional theory calculation.
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