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The interfacial electronic band structures of photovoltaic heterostructure devices greatly affect their light absorption and charge-transport properties and thus their photovoltaic performance. In this work, we report an enhanced ferroelectric photovoltaic effect in a semiconducting single-walled carbon nanotube (S-SWCNTs)/ferroelectric BiFeO3 (BFO) heterostructure. A wide range of light absorption was possible in this structure owing to the low bandgaps of the S-SWCNTs (0.2–2.1 eV) and BFO (2.2–2.7 eV). The heterostructure also enabled efficient charge separation owing to the strong built-in electric field resulting from the synergic effect of the formation of p–f–n junctions (p-type S-SWCNTs/ferroelectric (f) BFO/n-type Nb:SrTiO3) and the introduction of a polarization-mediated internal field in the ferroelectric BFO layer. Compared with a single-layer device (Pt/BFO/Nb:SrTiO3), the heterostructure device (Pt/S-SWCNTs/BFO/Nb:SrTiO3) exhibited substantial enhancement of the photovoltaic performance. The open-circuit photovoltage and short-circuit photocurrent density reached up to 0.23 V and −7.52 mA cm−2 (corresponding to a photo-conversion efficiency of 4.40%) under one-sun illumination, respectively, after optimization of the ferroelectric layer thickness and appropriate interfacial band alignment. Moreover, by applying switchable electric polarization, this heterostructure could be tuned, enabling the development of controllable photovoltaic devices. Our findings demonstrate that the synergistic integration of materials with different functionalities is a promising approach for the design of photovoltaic devices with tunable performance. [ABSTRACT FROM AUTHOR]

Here, we examine grain boundaries (GBs) with respect to non-GB regions (grain surfaces (GSs) and grain interiors (GIs)) in high-quality micrometer-sized perovskite CH3NH3PbI3 (or MAPbI3) thin films using high-resolution confocal fluorescence-lifetime imaging microscopy in conjunction with kinetic modeling of charge-transport and recombination processes. We show that, contrary to previous studies, GBs in our perovskite MAPbI3 thin films do not lead to increased recombination but that recombination in these films happens primarily in the non-GB regions (i.e., GSs or GIs). We also find that GBs in these films are not transparent to photogenerated carriers, which is likely associated with a potential barrier at GBs. Even though GBs generally display lower luminescence intensities than GSs/GIs, the lifetimes at GBs are no worse than those at GSs/GIs, further suggesting that GBs do not dominate non-radiative recombination in MAPbI3 thin films. [ABSTRACT FROM AUTHOR]

A mechanism underlying the appearance of a preferred orientation in anodized amorphous TiO2 nanotube arrays (NTAs) was studied. Transmission electron microscopic analyses of preferred-oriented nanotube arrays (p-NTAs) reveal that at an optimum water content (~2 wt%), large single crystalline domains oriented along ＜001＞ grow from the outer wall to the inner wall to minimize the surface energy. In stark contrast, excessive water content (5 wt%) in the electrolyte leads to sporadic multiple nucleation of randomly oriented anatase crystallites in amorphous medium at the early stage of crystallization, which results in the formation of randomly oriented nanotube arrays (r-NTAs). During subsequent thermal annealing, multiple nucleation sites hindered the growth of the ＜001＞-oriented grains from the outer wall. When the water content in an ethylene glycol-based electrolyte is optimized by reducing the uncertainty of water content, the X-ray diffraction patterns of NTAs exhibited a 200 times increase in the intensity ratio of (004) to (200) peaks of the anatase phase. p-NTAs exhibit ~5 times lower electrical resistance than r-NTAs, which supports the idea that improving the preferred orientation of NTAs is a promising method for developing efficient electronic devices. [ABSTRACT FROM AUTHOR]

MgO-coated TiO2 nanoparticle (NP)-based electron collecting layers were fabricated to prevent charge recombination at the methylamine lead iodide/TiO2 interface in perovskite solar cells. The open circuit voltage (Voc) and fill factor (ff) of perovskite solar cells based on MgO-coated TiO2 charge collectors were 0.89 V and 71.2%, respectively. These values were 4.7% and 6.1% higher than the pure TiO2 based perovskite solar cells. Transient photovoltage decay data exhibited recombination times for MgO-coated TiO2 NP-based perovskite solar cells about three times longer than those of TiO2 NP based solar cells. The longer recombination time was responsible for enhancing the Voc and ff of MgO-coated TiO2 NP-based perovskite solar cells. By employing a MgO nanolayer, we observed that the power conversion efficiency (PCE) was increased from 11.4% to 12.7%, demonstrating that MgO ultrathin nanolayers are able to efficiently retard charge recombination in perovskite solar cells. [ABSTRACT FROM AUTHOR]

Here, we examine grain boundaries (GBs) with respect to non-GB regions (grain surfaces (GSs) and grain interiors (GIs)) in high-quality micrometer-sized perovskite CH 3 NH 3 PbI 3 (or MAPbI 3 ) thin films using high-resolution confocal fluorescence-lifetime imaging microscopy in conjunction with kinetic modeling of charge-transport and recombination processes. We show that, contrary to previous studies, GBs in our perovskite MAPbI 3 thin films do not lead to increased recombination but that recombination in these films happens primarily in the non-GB regions (i.e., GSs or GIs). We also find that GBs in these films are not transparent to photogenerated carriers, which is likely associated with a potential barrier at GBs. Even though GBs generally display lower luminescence intensities than GSs/GIs, the lifetimes at GBs are no worse than those at GSs/GIs, further suggesting that GBs do not dominate non-radiative recombination in MAPbI 3 thin films.

Herein, we report on the synthesis of phase-pure rutile walnut-like TiO(2) (W-TiO(2)) spheres composed of single-crystalline nanorod-building blocks using a surfactant-free non-aqueous acidic modified "benzyl alcohol route". Based on the various HCl concentration- and reaction time-dependent experiments, an effect of hydrochloric acid on the phase formation mechanism in a non-aqueous system is suggested. As anodes for Li-ion batteries, the W-TiO(2) sphere electrodes exhibited superior cycling performance at a rate of 0.2 C without any conducting layers coated onto the anodes; this result is attributed to their high crystallinity and large surface area.

We demonstrated the formation of monodispersed spherical aluminum hydrous oxide precursors with tunable sizes by controlling the variables of a forced hydrolysis method. The particle sizes of aluminum hydrous oxide precursors were strongly dependent on the molar ratio of the Al(3+) reactants (sulfates and nitrates). In addition, the systematic phase and morphological evolutions from aluminum hydrous oxide to γ-alumina (Al(2)O(3)) and finally to α-Al(2)O(3) through thermal dehydrogenation were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). After annealing the amorphous aluminum hydrous oxide in air at 900 °C and 1100 °C for 1 h, we observed complete conversion to phase-pure γ- and α-Al(2)O(3), respectively, while maintaining monodispersity (125 nm, 195 nm, 320 nm, and 430 nm diameters were observed). Furthermore, both γ- and α-Al(2)O(3) were found to be mesoporous in structure, providing enhanced specific surface areas of 102 and 76 m(2) g(-1), respectively, based on the Brunauer-Emmett-Teller (BET) measurement., (This journal is © The Royal Society of Chemistry 2011)