This Review focuses on recent developments in the use of ZnO nanostructures for dye‐sensitized solar cell (DSC) applications. It is shown that carefully designed and fabricated nanostructured ZnO films are advantageous for use as a DSC photoelectrode as they offer larger surface areas than bulk film material, direct electron pathways, or effective light‐scattering centers, and, when combined with TiO2, produce a core–shell structure that reduces the combination rate. The limitations of ZnO‐based DSCs are also discussed and several possible methods are proposed so as to expand the knowledge of ZnO to TiO2, motivating further improvement in the power‐conversion efficiency of DSCs.

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We report high thermoelectric performance in nanostructured p-type PbS, a material consisting of highly earth abundant and inexpensive elements. The high level of Na doping switched intrinsic n-type PbS to p-type and substantially raised the power factor maximum for pure PbS to ~9.0 μW cm(-1) K(-2) at >723 K using 2.5 at. % Na as the hole dopant. Contrary to that of PbTe, no enhancement in the Hall coefficient occurs at high temperature for heavily doped p-type PbS, indicating a single band model and no heavy hole band. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding SrS or CaS, which form a combination of a nanostructured/solid solution material as determined by transmission electron microscopy. We find that both nanoscale precipitates and point defects play an important role in reducing the lattice thermal conductivity, but the contribution from nanoscale precipitates of SrS is greater than that of CaS, whereas the contribution from point defects in the case of CaS is greater than that of SrS. Theoretical calculations of the lattice thermal conductivity based on the modified Callaway model reveal that both nanostructures and point defects (solid solution) effectively scatter phonons in this system. The lattice thermal conductivity at 723 K can be reduced by ~50% by introducing up to 4.0 at. % of either SrS or CaS. As a consequence, ZT values as high as 1.22 and 1.12 at 923 K can be achieved for nominal Pb(0.975)Na(0.025)S with 3.0 at. % SrS and CaS, respectively. No deterioration was observed after a 15 d annealing treatment of the samples, indicating the excellent thermal stability for these high performance thermoelectrics. The promising thermoelectric properties of nanostructured PbS point to a robust low cost alternative to other high performance thermoelectric materials.

Since the advent of dye-sensitized solar cells (DSCs), which have achieved $11% of power conversion efficiency (PCE) in TiO 2 -based photoelectrodes, a lot of efforts have been devoted to make low-cost, light-weight, high-performance photovoltaic devices. [1][2][3] Nanostructured metal oxides are one of key factors in determining the PCE of DSCs, because the nanostructured networks provide a huge surface area to accommodate a large quantity of dye molecules that relate to the light harvesting of a photoelectrode in DSCs.ZnO is a good alternative of TiO 2 because it has a similar band gap but higher electron mobility than TiO 2 . [4][5][6][7] The mobility of ZnO is about 115-155 cm 2 V À1 s À1, much higher than that of TiO 2 , $10 À5 cm 2 V À1 s À1. Recently, DSCs with photoelectrodes made of submicrometer-sized aggregates of ZnO nanocrystallites demonstrated a PCE of 5.4% due to much enhanced light scattering without compromising the surface area for dye molecule adsorption. [8][9][10] A porous structured ZnO aggregates of nanocrystallites were thought to be helpful to retain their high surface area. Although this PCE is still lower than that of TiO 2 DSCs, it doubled the PCE of ZnO nanocrystallite DSCs.Atomic layer deposition (ALD) has been used to introduce extremely thin and conformal coating due to its unique self-limiting nature and low growth temperature; lots of semiconductor materials like TiO 2 , ZnO, SnO, and Al 2 O 3 can be grown by ALD. [11][12][13] In this study, we utilized ALD to deposit ultrathin TiO 2 layer on the porous structure of ZnO aggregates and demonstrated much enhanced PCE of ZnO DSC with photoelectrodes made of submicrometer-sized aggregates of ZnO nanocrystallites.As illustrated schematically in Figure 1a-c, TiO 2 ultrathin layer deposited by ALD would form a complete and conformal coverage on the surface and even inside pores of ZnO that would otherwise be exposed to dye electrolyte during the dye loading. Consequently, all the dye molecules would adsorb onto the surface of TiO 2 coating. Such an ultrathin and conformal ALD coating would not change the morphology the underline ZnO structures as shown in Figure 1e and 1f. The coating of TiO 2 layer on the surface of ZnO by ALD is presumably so thin that would not affect any detectable change in the morphology by means of scanning electron microscopy (SEM). Brunauer Emmett Teller (BET) results demonstrate that micropores inside each aggregate still remain after ALD, indicating that the porous structure of ZnO is preserved. As shown in Table 1, the slight decrease in the size and volume of the micropore was observed due to the introduction of ALD-TiO 2 layer. In addition, the connections between adjacent ZnO nanocrystallites would retain to ensure a favorable electron motion through ZnO (as suggested in Fig. 1d). Such structure would improve the surface stability with enhanced dye loading on the ZnO surface, while retains the advantage of high electron mobility in ZnO.It is reported that the growth rate of TiO 2 at the substrate tempera...

The diverse reactivity of 5-hydroxymethylfural (HMF) in Pd/C-catalyzed reactions is described with emphasis on the role of additives that affect selectivity.

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