Development of block copolymer-templated crack-free mesoporous anatase-TiO_2 film: tailoring sol-gel and EISA processing parameters and photovoltaic characteristics

摘要

A new facile strategy for preparation of mesoporous anatase-TiO_2 films by a combination of sol-gel and evaporation-induced self-assembly (EISA) processes aided by tri-block Pluronic F127 is reported. Two major parameters, sol preparation and EISA processing parameters, are identified for preparation of mesoporous crack-free films with desired thickness. The mesoporous crack-free films with thickness of 650 nm can be obtained with low water: precursor molar ratio (e.g., 2.5:1) under aging in 10 % relative humidity for 72 h at the low temperature of 5 ℃. Although template: precursor molar ratio and annealing temperature show little influence on preparation of crack-free films the optimum values are determined 0.005:1 and 350 ℃, respectively. Reducing the aging temperature down to 5 ℃ not only hinders the anatase-to-rutile phase transformation but also retards crystal growth. Furthermore, Brunauer-Emmett-Teller and Barrett-Joy-ner-Helenda results show that the isotherm corresponding to synthesized powders represents a combination of types Ⅱ and Ⅳ corresponding to mesoporous materials with average pore size in the range 5.8-8.8 nm and BET surface area of 72-99 m~2/g. UV-Vis absorption spectrum of prepared mesoporous TiO_2 film displays a blue shift relative to that of bulk TiO_2 due to the quantum size effect. The mesoporous TiO_2 film prepared under optimized conditions has good microstructural and optical properties for dye-sensitized solar cell (DSSC) applications. The DSSC made of optimized mesoporous TiO_2 film shows cell efficiency and short circuit current density of 6.31 % 15.23 mA/cm~2, respectively.