D-sorbitol-induced phase control of TiO2 nanoparticles and its application for dye-sensitized solar cells.

Shoyebmohamad F Shaikh,Yun Jeong Hwang,Oh-Shim Joo,Rajaram S Mane,Byoung Koun Min

doi:10.1038/srep20103

Abstract

Using a simple hydrothermal synthesis, the crystal structure of TiO2 nanoparticles was controlled from rutile to anatase using a sugar alcohol, D-sorbitol. Adding small amounts of D-sorbitol to an aqueous TiCl4 solution resulted in changes in the crystal phase, particle size, and surface area by affecting the hydrolysis rate of TiCl4. These changes led to improvements of the solar-to-electrical power conversion efficiency (η) of dye-sensitized solar cells (DSSC) fabricated using these nanoparticles. A postulated reaction mechanism concerning the role of D-sorbitol in the formation of rutile and anatase was proposed. Fourier-transform infrared spectroscopy, 13C NMR spectroscopy, and dynamic light scattering analyses were used to better understand the interaction between the Ti precursor and D-sorbitol. The crystal phase and size of the synthesized TiO2 nanocrystallites as well as photovoltaic performance of the DSSC were examined using X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and photocurrent density-applied voltage spectroscopy measurement techniques. The DSSC fabricated using the anatase TiO2 nanoparticles synthesized in the presence of D-sorbitol, exhibited an enhanced η (6%, 1.5-fold improvement) compared with the device fabricated using the rutile TiO2 synthesized without D-sorbitol.

Highlights

Many solution based methods have been reported for the synthesis of TiO2 nanoparticles, such as sol–gel[10], solvothermal[11], and hydrolysis[12] etc
Cheng et al explained the difference in the crystallization of anatase and rutile TiO2 by the hydrolysis of TiCl4 in an aqueous solution using ligand field theory[26], and the crystallization occurred via dehydration between partially hydrolyzed Ti(OH)nCl6-n complexes
As-prepared TiO2 had a rutile crystal phase when prepared via the hydrolysis of the TiCl4 precursor in an acidic environment, whereas pure anatase TiO2 was obtained when D-sorbitol was added into the precursor solution

Summary

Introduction

Many solution based methods have been reported for the synthesis of TiO2 nanoparticles, such as sol–gel[10], solvothermal[11], and hydrolysis[12] etc. Various parameters are being suggested to affect the crystallinity as well as the size of the TiO2 product. The pH of the precursor solutions was suggested to affect the growth mechanisms and crystal structures of the TiO2 nanocrystals[16]. The acidic/alkaline conditions employed in the synthesis of TiO2 nanoparticles were observed to affect the performance of DSSC17. The aim of the present work is to prepare TiO2 nanocrystals with pure anatase phase using a low-temperature (< 200 °C) hydrothermal method. We observed that reactions proceeds even in the absence of D-sorbitol the resultant TiO2 product was pure rutile rather than anatase. The driving force for the anatase TiO2 synthesis was studied from the complex species of D-sorbitol with Ti cations coupled through hydroxyl ions in the solution. The present method is a facile single-step process, and TiO2 nanoparticles prepared in this present work are chemically, environmentally and mechanically stable for several days, justifying their long-term uses

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Results

Conclusion