One major problem in the application of TiO2 and other oxides as an electron transport layer and optical window in perovskite solar cells (PSCs) is the nonstoichiometric defects related to oxygen vacancies. We report the studies of a TiO2 compact layer annealed in ambient air and in an oxygen environment, and the consequences on planar PSC performance. Chemical analysis and optical studies indicate that oxygen vacancy density can be significantly reduced by changing annealing conditions, leading to higher optical transmission of the TiO2 layer and retarded carrier recombination in the PSC. The carrier dynamics studies found that the electron recombination lifetime was significantly increased. With an improved electron transport layer, the power conversion efficiency of PSCs with a TiO2 compact layer annealed in oxygen was increased from 13.58% to 15.85%, due to a largely enhanced current density when compared to the control PSCs with TiO2 annealed in ambient air.

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at − 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm−2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications. Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-017-0162-4) contains supplementary material, which is available to authorized users.

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Assembling two-dimensional graphene and VO2(B) nanomaterials into an ordered three-dimensional forest structure for high performance lithium ion batteries.