Natural Sensitizer for Dye-Sensitized Solar Cells Using Three Layers of Photoelectrode Thin Films with a Schottky Barrier

Chang Chang

doi:10.3844/ajnsp.2010.13.22

Abstract

Problem statement: This study combines Au nanoparticles with TiO2 nanoparticles to form a Schottky barrier and applies it to the photoelectrode thin film of Dye-Sensitized Solar cells (DSSCs). Approach: First, commercial TiO2 powder (Degussa P25) was put into the alkaline solution to prepare TiO nanotubes (Tnt) by a hydrothermal process. Tnt were sintered at 550° to obtain TntC550 particles and fabricated into a translucent sol by two hydrothermal treatments and baked at 180° to acquire H180 particles. H180 and TntC550 were spread into transparent polymer films by a doctor blade. H180 serves as the first layer and TntC550 the second, with both were sintered at 450°. The third layer uses hydrogen tetrachloroautate (HAuCl4) and trisodium citrate (C6H5Na3O7) to prepare Au nanoparticles by salt reduction. Natural dyes of bougainvillea leaves for chlorophyll and blueberries for anthocyanin were employed in this study. Extracted chlorophyll and anthocyanin dyes were also blended in the proportion of 1: 1 as a mixed dye and these three different natural dyes were compared to compare their photoelectric conversion efficiencies. Electrolyte and counter electrode (Pt) were added to form the sandwich structure of DSSCs. After being sealed, DSSCs were tasted for fill factor, photoelectric conversion efficiency and incident photon-to-current conversion efficiency. Results: Spherical Au nanoparticles around 27nm were adhered to the TntC550 make a film by self-assembly to complete the preparation of the third of photoelectrode thin film of DSSCs. Results from the experimental tests show that for the dye mixtures, photoelectric conversion efficiency of DSSCs in this study can reach 0.75% with the VOC of 0.56 V and JSC of 2.93 mA/cm2 and FF of 0.47. Conclusion: It can be seen from the current density logarithm and voltage diagram that the prepared Au nanoparticles produce Schottky barriers on the surface of TiO2. Due to the Schottky barrier, electrons were unable to go back to the dye molecules or electrolyte, thus effectively enhancing the electronic conversion efficiency.

Highlights

Pollution has increasingly become a worldwide concern in the past few decades
The high energy conversion efficiency of the widely used N719 sensitizer [bis(tetrabutylammonium) cis-dithiocyanatobis (2,2′bipyridine-4-COOH,4′-COO−), ruthenium(II)] and other related Ru-bipyridyl- based dyes derives from the spatial separation of the donor– the Lowest Unoccupied Molecular Orbital (LUMO), which is close to the TiO2 surface and the acceptor, the highest occupied molecular orbital (HOMO) resulting in injection which is much faster than recombination (Mohran, 2005; Liu and Wang, 2010)
TiO nanotubes (Tnt) hydrothermally fabricated by 550°C calcinating treatment (Tnt-C550) and TiO2 nanoparticles (H180) obtained by exposing Tnt to two cycles of hydrothermal treatment We investigate the differences in structure, morphology and the level of light scattering of these three materials

Summary

Introduction

Pollution has increasingly become a worldwide concern in the past few decades. how to enhance the Energy technology is one of the most important efficiency of natural energy use and to recycle technologies. A photoelectrode fabricated from TiO2 nanotubes can increase the short-circuit current and the photoelectric conversion efficiency of DSSCs. In addition, TiO2 particles fabricated by different methods can increase the length of the path along which photons pass via the properties of light scattering if TiO2 particles with good properties of optical transmittance and scattering properties are used. With very high chemical energy, the surface of metallic nanoparticles exhibit resonance absorption when the incident light frequency approaches the surface plasma frequency of Au nanoparticles, causing the electrons of Au nanoparticles to move from their orbit to the surface plasma absorption band and producing chemical bonds with molecules This phenomenon will directly affect optical properties and can be applied in DSSCs (Akbarzadeh et al, 2009; Gun et al, 2011). This study uses hydrothermal treatment to prepare Tnt. To increase photoelectric conversion efficiency, this study adopts two different morphologies of TiO2 materials.

Methods

Results

Conclusion