Mesoporous NiO is used as p-type material in photoelectrochemical energy conversion devices. The presence of two kinds of hole traps can affect device performance. Here, after band-gap excitation, the relaxation of the hole into two different traps was observed and characterized.

In this study, a core-shell NiO-dye-TiO mesoporous film was fabricated for the first time, utilizing atomic layer deposition technique and a newly designed triphenylamine dye. The structure of the film was confirmed by SEM, TEM, and EDX. Excitation of the dye led to efficient and fast charge separation, by hole injection into NiO, followed by an unprecedentedly fast dye regeneration (t ≤ 500 fs) by electron transfer to TiO. The resulting charge separated state showed a pronounced transient absorption spectrum caused by the Stark effect, and no significant decay was found within 1.9 ns. This indicates that charge recombination between NiO and TiO is much slower than that between the NiO and the reduced dye in the absence of the TiO layer (t ≈ 100 ps).

Solid state p-type dye sensitized NiO-dye-TiO 2 core-shell solar cells with an organic dye PB6 were successfully fabricated for the first time.With Al 2 O 3 as an inner barrier layer, the recombination process between injected holes in NiO and injected electrons in TiO 2 was significantly suppressed and the charge transport time was also improved.p-Type dye sensitized solar cells (p-DSCs) have attracted intense interest due to their different charge transfer kinetics with respect to more common studied n-DSCs, 1-3 and the potential application in tandem solar cells 4-6 and solar fuel devices. 7-9The conventional p-DSCs are based on liquid redox electrolytes. To avoid having a liquid phase in the p-DSCs, we have recently proposed and proven the concept of solid state p-DSCs, in which a solid state phenyl-C61-butyric acid methyl ester (PCBM) was used as an electron transport material (ETM) between the dye sensitized photocathode and the back contact. 10 Optimization of photosensitizer represents one strategy to improve the performance of this kind of solar cells. 11,12 Inspired by the conventional dye sensitized TiO 2 solar cells, we proposed that TiO 2 should be an alternative ETM to PCBM due to the fast electron injection from dyes into TiO 2 13,14 and good electron transport property. 15 Thus, we recently fabricated a dye sensitized NiOdye-TiO 2 core-shell film and, in contrast to previous work, [16][17][18] the nanoporous NiO film was first sensitized with the dye and a TiO 2 coating was applied afterwards. This dye sensitized coreshell film showed ultrafast hole (t 1/2 o 120 fs) and electron injection into NiO and TiO 2 respectively, resulting in ultrafast dye regeneration upon electron injection, t 1/2 r 500 fs. 19 In the present work, we proved that the dye sensitized NiO-dye-TiO 2 core-shell mesoporous film can be used for fabrication of solid state p-type dye sensitized solar cells. We also show the effect of an Al 2 O 3 inner barrier layer between NiO and TiO 2 on the performance of solar cell. Fig. 1 shows the configuration and working principle of the proposed p-type dye sensitized NiO-dye-TiO 2 core-shell solar cells. The donor-p-acceptor dye PB6 was utilized as photosensitizer since its reduction/oxidation potentials in excited state match with the valence band of NiO and conduction band of TiO 2 . 19The fabrication of the photoelectrode used in this study can be described briefly as follows. A compact NiO layer (60 nm) was sputtered onto a FTO substrate, then a mesoporous NiO layer (1.3 mm) was prepared by doctor-blading NiCl 2 gel on FTO glass and sintered at 450 1C for 0.5 h.20 Subsequently, the NiO electrode was immersed into 0.2 mM PB6 dichloromethane (DCM) solution overnight. The dye loading in the film was determined to be 31.6 nmol cm À2 by desorption experiment (see ESI †). After rinsing with methanol, the dye sensitized NiO film was dried and coated with metal oxides by atomic layer deposition (ALD). For NiO-PB6-TiO 2 photoelectrode, ca. 10 nm TiO 2 layer was coated directly on a dye sensit...

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A ruthenium complex, porphyrin sensitizer, fullerene acceptor molecular pentad has been synthesized and a long-lived hole-electron pair was achieved in aqueous solution by photoinduced multistep electron transfer: Upon irradiation by visible light, the excited-state of a zinc porphyrin ( ZnP*) was quenched by fullerene (C ) to afford a radical ion pair, (ZnP -C ). This was followed by the subsequent electron transfer from a water oxidation catalyst unit (Ru ) to ZnP to give the long-lived charge-separated state, Ru -ZnP-C , with a lifetime of 14 μs. The ZnP worked as a visible-light-harvesting antenna, while the C acted as an excellent electron acceptor. As a consequence, visible-light-driven water oxidation by this integrated photosynthetic model compound was achieved in the presence of sacrificial oxidant and redox mediator.