Academic journal article American Academic & Scholarly Research Journal

Sensitization of Nanocrystalline Titanium Dioxide Solar Cells Using Natural Dyes: Influence of Acids Medium on Coating Formulation

Academic journal article American Academic & Scholarly Research Journal

Sensitization of Nanocrystalline Titanium Dioxide Solar Cells Using Natural Dyes: Influence of Acids Medium on Coating Formulation

Article excerpt

Abstract. Dye Sensitzed solar cells (DSSC) has drawn attention as an alternative to the silicon based solar cells due to their low fabrication cost and reasonably high efficiency. This paper presents an approach on the development of DSSC and the photoelectrochemical effect and conversion efficiency available natural dye sensitized Titanium dioxide (TiO^sub 2^) photoelectrode with respect to acid treatment of coating formulation. Acid treatment on TiO^sub 2^ paste was observed using an organic acid (citric acid) and an inorganic acid (nitric acid) considering a base natural dye (red spinach). Optimal concentration of these acids (organic and inorganic) was determined by cell performance. Five different natural dyes were used as sensitizers of DSSC and their performance was observed considering photoelectrochemical output and UV-visible absorption using optimized acid concentrations. Citric Acid treated cells with red spinach dye as sensitizer produced the best performance with 1mAcm^sup -2^ current density with 505mV potential. It was found that DSSC showed better photovoltaic performance and higher conversion efficiency when the TiO^sub 2^ paste was treated by organic acid than inorganic acid and red spinach dye proved to be the best sensitizer.

Keywords: Dye Sensitized Solar Cell, Nanocrystalline, Natural Sensitizers, Photoelectrochemical output, Acid medium.

1. INTRODUCTION

Silicon based solar cells were the most popular before the emerging of dye-sensitized solar cells. These solid-state junction devices have dominated photovoltaic industry. Since Grätzel et al. developed dye-sensitized solar cells (DSSCs) in 1991, these have attracted a significant devotion due to their environmental friendliness and low cost of production along with reasonably high efficiency. A DSSC is composed of a nanocrystalline porous semiconductor (TiO2) electrode-absorbed dye, a counter electrode, and an electrolyte containing iodide and tri-iodide ions. In DSSCs, the dye as a sensitizer plays a key role in absorbing sunlight and transforming solar energy into electric energy.

In conventional silicon based solar cells, silicon both absorbs the sunlight and acts as the charge carrier. But in DSSC, light is absorbed by the sensitizer and charge separation takes place by the photo-induced electron injection from dye to sensitizer. In contrast to conventional solar cells DSSC is a photoelectrochemical cell. It resembles natural photosynthesis in two respects like it uses organic dye based on chlorophyll to absorb lights and produces a flow of electrons. And it uses multiple layers to enhance both the light absorption and electron collection efficiency. The photoelectrode plays one of the most important roles in high efficiency of DSSC because this is the first step towards electron transport. So lots of efforts have been reported for the modification of the photo electrode. Titanium dioxide (TiO2) as a photocatalyst for degrading organic pollutions has attracted much attention because of its various advantages. Unfortunately, the technological use of TiO2 is limited by its wide band gap (3.2eV for anatase), which requires UV light irradiation to obtain its photocatalytic activity. Because UV light only accounts for a small fraction (5%) of the sun's energy compared to visible light (45%), any attempt making TiO2 absorb visible light will have a profound positive effect on its visible photocatalytic performance. For this purpose, various efforts have been directed toward the development of visible-light responsive TiO2 materials. One was based on the chemical/physical adsorption of dye molecules on TiO2 surface for construction of dye-sensitized photocatalysts that could work under visible light irradiation. Another approach utilized the chemical reaction between Ti- OH and phenolic hydroxyl of organic compounds (not dye), such as catechol, salicylic and binaphthol , to form surface complexes on TiO2 surface and to realize visible light absorption. …

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