Journal Information
Journal ID (publisher-id): chemical
Title: Journal of the Korean Chemical Society
Translated Title (ko): 대한화학회지
ISSN (print): 1017-2548
ISSN (electronic): 2234-8530
Publisher: Korean Chemical Society대한화학회
All chemicals were used as received; Cadmium nitrate tetrahydrate [Cd(NO3)2·4H2O, ≥99.0%], cadmium acetate dihydrate [Cd(CH3COO)2·2H2O, reagent grade, 98.%], sodium sulfide nonahydrate (Na2S·9H2O), sodium sulfide (Na2S), antimony(III) chloride (SbCl3, ACS reagent, ≥99.0%), silver nitrate (AgNO3, ACS reagent, ≥99.0%), bismuth nitrate pentahydrate [Bi(NO3)3·5H2O, ACS reagent, ≥98.0%], copper nitrate hydrate [Cu(NO3)2·xH2O, 99.999%], lead nitrate [Pb(NO3)2, 99.999%], and triethanolamine (TEA, reagent grade, 98%) were purchased from Sigma-Aldrich. Ethanol and methanol were of HPLC-grade.
0.20 M Co(II) complex of [Co(bpy)3](PF6)2, 0.05 M Co(III) complex of [Co(bpy)3](PF6)3, and 0.10 M, lithium perchlorate (LiClO4) were dissolved in acetonitrile. Here, bpy stands for bipyridine.
For a thin TiO2 blocking layer, fluorine-doped tin oxide (FTO)-coated glass electrode (Solaronix, 8 Ω/□) was treated with 40 mM TiCl4 aqueous solution for 30 min at 70 ℃ and then washed with pure water. The electrode was gradually heated to 500 ℃. Using screen-printing machine and commercial TiO2 pastes, about 5 μm thick TiO2-blend layer (Dyesol, 18NR-AO; TiO2 particle size 20~450 nm) which is responsible for adsorbing most of sensitizers in the electrode and ~4 μm scattering layer (Dyesol, WER2-O; TiO2 particle size 150~250 nm) were deposited sequentially and then sintered up to 500 ℃ to make a mesoporous TiO2 film. Finally, the typical TiCl4 post-treatment was applied as the same manner with the pre-treatment of TiCl4. A platinium (Pt)-counter electrode was prepared by following procedure; a 10 nM solution of chloroplatinic acid hexahydrate (H2PtCl6·6H2O, Sigma-Aldrich) in ethanol was dropped onto the FTO electrode and dried in air for 20 min. Then, the electrode was annealed gradually to 450 ℃ for 30 min under atmospheric conditions.
To grow CdS QD sensitizer, the typical SILAR process was done by alternative dipping of as-prepared FTO/TiO2 electrodes in 0.05 M Cd(NO3)2 and 0.05 M Na2S·9H2O aqueous solutions, respectively for 1 minute, which was repeated five times. Between dipping, a washing step was included for 1 minute in pure water. After depositing CdS by following the SILAR process, the cation-exchange process was done by dipping the as-deposited CdS/TiO2/FTO electrode into 0.10 M AgNO3, Bi(NO3)3, Cu(NO3)2, or Pb(NO3)2 aqueous solution for 30 seconds [0.10 M Bi(NO3)3, was saturated due to its low solubility in water]. The yellow color of CdS/TiO2/FTO electrode was changed immediately by a cation-exchange for new target QDs.
SILAR and cation exchange processes were used to prepare Sb2S3 QD sensitizer. For SILAR-growing of CdS, a 0.10 M Cd(CH3COO)2· 2H2O and 1 M triethanolamine in ethanol/water (1:1, v/v), and a 0.10 M Na2S·9H2O in methanol/water (1:1, v/v) were used for each cationic and anionic source. The mesoporous TiO2 film-covered FTO electrode was dipped into Cd2+ solution, pure ethanol (then dried in air), the S2- solution, and then pure methanol (then dried in air) successively for 1 min each. Such immersion cycle was repeated 9 times. After this SILAR process, the electrode of TiO2/CdS was immersed into a 0.10 M SbCl3 in ethanol for 10 min to induce cation exchange process at room temperature. A post-treatment of annealing in N2 atmosphere was applied by increasing temperature from 100 ℃ to 300 ℃ for 20 min. The color change was observed on the TiO2/Sb2S3 electrode during the annealing procedure, which was orange before annealing and gradually turned dark brown as the temperature increased. But, in the case of CdS, there was only a slight change in the intensity of color.
A 0.020 M SbCl3 in ethanol and 0.020 M Na2S in ethanol were used for each cationic and anionic source for depositing Sb2S3 by the SILAR process, which was repeated 5 times with a dipping time of 90 seconds each. Between the dipping in each precursor solution, the electrode was washed in pure ethanol in 3 minutes. The as-prepared Sb2S3-deposited electrode was annealed to 300 ℃ for 20 minutes under nitrogen.
To make QD-sensitized solar cells with a counter electode of the typical platinized FTO glass, the as-prepared QD-sensitized photoanode and Pt-cathode were combined by hot-press machine through the Surlyn film, and the electrolyte solution was injected through a pre-drilled hole through the counter electrode.
The current-voltage and open-circuit voltage decay characteristics were analyzed under a standard illuminating condition (1 sun, 100 mW cm-2) using a solar simulator (Peccell, PEC-L01) and a potentiostat (IVIUM, Compactstat). Various irradiance intensities from 0.1 to 1.0 sun could be provided with optical attenuators. The incident photon-to-current efficiency (IPCE) data were collected by a light source (ABET 150W Xenon lamp, 13014) with a monochromator (DONGWOO OPTORN Co., Ltd., MonoRa-500i) and a potentiostat (IVIUM, Compactstat) based on DC method without chopper and light bias. Optical absorbance was measured with a UV-VIS spectrophotometer (PerkinElmer Lambda 25).