Controlled Oriented Attachment of Bipyramidal‐Shaped Anatase TiO₂ and Their Enhanced Performance in Dye‐Sensitized Solar Cells

Abstract

Al ow-cost hydrothermalm ethodw as used to synthesize highpurity bipyramidal single-crystals of TiO 2 enclosed with high percentage of (101) facets. The oriented attachment behavior can be controlled by fine tuning the reaction temperature. This played an importantr ole in determining the crystal growth along [001]d irection resulting in the self-assembly of the bipyramid crystals into connected ones to form single-crystal nanrods without the loss of surface area. In addition, the relationship between oriented attachment and the photovoltaic performance of such anatase TiO 2 nanocrystals in photoanodes of DSCs was investigated. The highly oriented sample reached am aximum overall energy conversion efficiency of 8.63 %. These results further illustrated that the highly oriented samples have superior charget ransport ability derived from the enhanced long-range atomica rrangementw ith reduced grain boundaries and comparable uptake of dye molecules.Dye-sensitized solarc ells (DSCs) have drawn considerable attention as they hold promise for low-cost, solar-to-electricity energy conversion. [1] Recently,a ne nergy conversion efficiency over 13 %w as demonstrated for DSCs and numerous studied have reported af urtheri ncreasei nt he efficiency by employing alternative sensitizers, [2][3][4][5] redox electrolytes, [3] and solid-state hole conductors. [6,7] However,p rogress is greatly restricted by the short diffusion length of sinteredT iO 2 films composed of nanoparticles (10-35 mm, as determined by the product of the electron diffusion coefficient and electron lifetime). [8,9] Such short electron diffusion length is determined by trapping/detrapping events alongt he sites of the electron traps that generally occur at the TiO 2 surfacea nd are of significant importance at the interface between TiO 2 nanoparticles. [10] In spite of the short electron diffusion length, anatase TiO 2 still plays acrucial role in DSCs as ar esult of its appropriate electronic band gap and remarkable chemical stability. [11][12][13][14][15] Therefore, it is highly desirable to develop an ew synthetic method of preparing anataseT iO 2 that leads to low electrical resistance without sacrificing surfacea rea.It is known that adjacent particles can be spontaneously self-organized by an "oriented attachment" mechanism;a s ac onsequence the particles can share ac ommon crystallographic orientation, followed by the union of these particles at ap lanar interface. [16][17][18] Thism echanism shed light on the assembly of bipyramidal-shaped anatase TiO 2 enabling both large surface area and high electron conductivity.O fs ignificant importance is the goal to further tune the extent of oriented attachment, which would result in considerable improvement of the performance of TiO 2 in variousd evices,p articularly for DSCs.Herein, we developed an ew synthetic strategy to produce bipyramidal-shapeda natase TiO 2 and more importantly,t hese crystalsc an be further attached along the [001]d irection to form connected nanorods through tuning the reaction co...

Crystal shape engineering of anatase TiO2 and its biomedical applications

“…24 We have employed a high-purity synthetic system with only Ti, H, and O elements, which also gave rise to bipyramid-shaped anatase crystals. 25 By the hydrothermal treatment of titanate nanowires, anatase TiO 2 crystals bounded with even 100% {101} facets can be yielded, which is the most thermodynamically stable facet. 22 In these processes, the active {001} facets were diminished by rapid growth or orientated attachment along the {001} direction under reaction conditions.…”

Critical roles of co-catalysts for molecular hydrogen formation in photocatalysis

“…T-001 and T-101 were synthesized by a hydrothermal process according to our previous studies [24,33]. For T-001, 5 mL of tetrabutyl titanate (Sinopharm, 98%) and 0.8 mL of hydrofluoric acid (Sigma-Aldrich, 48%) were added dropwise into a dried Teflon-lined stainless steel autoclave with a capacity of 50 mL under agitation.…”