Ethyl Cellulose and Cetrimonium Bromide Assisted Synthesis of Mesoporous, Hexagon Shaped ZnO Nanodisks with Exposed ±{0001} Polar Facets for Enhanced Photovoltaic Performance in Quantum Dot Sensitized Solar Cells

Abstract

Hexagon shaped mesoporous zinc oxide nanodisks (ZnO NDs) with exposed ±{0001} polar facets have been synthesized by using ethyl cellulose (EC) and cetrimonium bromide (CTAB) as the capping and structure directing agents. We have characterized ZnO NDs using analytical techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area analysis and proposed a plausible mechanism for the formation of ZnO NDs. EC molecules form a colloidal solution in a 1-butanol:water (3:1) solvent system having a negative zeta potential (ζ ≈ -32 mV) value which can inhibit CTAB assisted c-axis growth of ZnO crystal and encourage the formation of ZnO NDs. In the control reactions carried out in presence of only CTAB and only EC, formation of hexagonal ZnO nanorods (NRs) and ZnO nanosheets (NSs) composed of numerous ZnO nanoparticles are observed, respectively. Photovoltaic properties of ZnO NDs as compared to ZnO NRs, ZnO NSs, and conventional ZnO nanoparticles (NPs) are investigated by co-sensitizing with CdS/CdSe quantum dots (QDs). An ∼35% increase in power conversion efficiency (PCE, η) is observed in ZnO NDs (η ≈ 4.86%) as compared to ZnO NPs (η ≈ 3.14%) while the values of PCE for ZnO NR and ZnO NS based devices are found to be ∼2.52% and ∼1.64%, respectively. Enhanced photovoltaic performance of the ZnO NDs based solar cell is attributed to an efficient charge separation and collection, boosted by the exposed ±(0001) facets apart from the single crystalline nature, better light-scattering effects, and high BET surface area for sensitizer particle adsorption. Electrochemical impedance spectroscopy (EIS) analysis further reveals that the charge recombination resistance and photoinduced electron lifetime are substantially higher in the ZnO ND based device than in ZnO NR, ZnO NP, and ZnO NS based devices, which demonstrates a slower electron-hole (e(-)-h(+)) recombination rate and faster charge migration through the single crystalline ZnO NDs.

Porous Single‐Crystal‐Based Inorganic Semiconductor Photocatalysts for Energy Production and Environmental Remediation: Preparation, Modification, and Applications

“…Cellulose can also provide adsorption sites to direct the growth of PSC precursor. Hexagon shaped mesoporous zinc oxide nanodisks (ZnO NDs) with exposed {0001} polar facets have been prepared by hydrothermal‐calcination protocol using ethylcellulose (EC) and CTAB as morphology templating agents 68. In the synthesis, CTAB molecules are proposed to act decreasing the surface tension of the solution, dismissing the energy required to form a new phase.…”

“…Proposed synthetic route for ZnO PSC nanodisks (NDs) (Path 1), nanorods (NRs) (Path 2), and nanosheets (NSs) (Path 3) under three different reaction conditions using a mixture of CTAB and EC (Path 1), or only CTAB (Path 2), and only EC (Path 3). Reproduced with permission 68. Copyright 2015, American Chemical Society.…”

“…Then, the charge transfer follows a sensitization mechanism in photocatalytic reaction. As an example of sensitization mechanism, hexagon shaped ZnO PSC nanodisks with exposed {0001} facets were modified either by CdS quantum dots (QDs) via successive ionic layer adsorption and reaction (SILAR) process, or by CdSe QDs via chemical bath deposition (CBD) method, separately 68…”

Quantum dot sensitized solar cell: Recent advances and future perspectives in photoanode

“…Chetia et al [96] have fabricated hexagonal shaped mesoporous ZnO nano-disks using ethyl cellulose and cetrimonium bromide as capping agent and structural directing agent. The prepared ZnO nano-disks are used as a photo-anodic material for CdS/CdSe QDSSC and performance is compared with ZnO nanorod, nanosheets and nano-particle based solar cell.…”

A facile method for synthesis of graphene-coated hexagonal ZnO photocatalyst with enhanced photodegradation activity

“…However, HZO was found to exhibit obvious increasing efficiency, and the photocatalytic efficiency reached to 69% after 50 min. Compared with the irregular shape of CZO, HZO particles own hexagonal shape with thin thickness, which could generate considerable internal electric field and facilitate the separation of photogenerated electron-hole pairs [19]. The enhanced separation efficiency of photogenerated charges could increase the photodegradation activity of ZnO.…”