INTRODUCTION

Dye sensitized solar cells are next-generation solar cells based on innovative technology. Unlike conventional silicon-based solar cells, dye-sensitized solar cells consist primarily of photosensitive dye and other substances. A dye-sensitized solar cell is a low-cost solar cell. This cell is also known as the Gratzel cell & was invented by Michael Gratzel and Brian O’Regan. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectrochemical system. It belongs to the group of thin film solar cells.
Its price/performance ratio is high enough to compete with fossil fuel electricity generation. The reason of rising popularity of these cells is its low-cost materials & the fact that it does not require elaborate high end manufacturing apparatus.

STRUCTURE

A dye-sensitized solar cell consists of a layer of titanium dioxide nanoparticles, covered with a molecular dye that absorbs sunlight. Titanium dioxide is the preferred material because of its resistance to continuous electron transfer. However, it only absorbs a small fraction of the solar photons (those in the UV). The absorption is intensified by the molecular sensitizers of the dye molecules attached to the semiconductor surface, which absorbs a great portion of the solar light. The titanium dioxide is immersed under an electrolyte solution, above which is a platinum-based catalyst.

PROCESS

Sunlight falls onto the dye layer where it absorbs energy, which enables the dye to enter an excited state & emits electrons which is absorbed by the titanium dioxide. The electrons flow (by diffusion) toward the transparent electrode where they are collected for powering a load. After flowing through the external circuit, they are re-introduced into the cell on a metal electrode on the back, flowing into the electrolyte. The electrolyte then transports the electrons back to the dye molecules.

DIFFERENCE FROM THE TRADITIONAL SILICON CELL

In the dye-sensitized solar cell, the bulk of the semiconductor is used solely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte. This way it is different from the traditional silicon cell, where the silicon acts as both the source of photoelectrons, as well as providing the electric field to separate the charges and create a current.

MEASURES TO INCREASE THE EFFICIENCY

• The dye molecules can be modified to increase the range where light can be absorbed. The absorption of light can also be increased by increasing the dye molecules absorbed in titanium dioxide.
• Internal resistance can be reduced by modifying the electrode structure and electrolyte.
• The efficiency of the solar cell can also be enhanced by increasing the aperture ratio.
• A semiconductor material is used as a platform to hold large numbers of the dye molecules to increase the number of molecules for any given surface area of cell, since the dye molecules are quite small. This is done to capture a reasonable amount of the incoming light.

ADVANTAGES

• Dye sensitized solar cells are the most efficient third-generation solar technology available & is greatly used in applications like rooftop solar collectors. The power production efficiency is around 11%, as compared to thin-film technology cells which are between 5% and 13%, and traditional commercial silicon panels which operate between 12% and 15%.
• In a silicon solar cell, it acts both as a source of electrons as well as an electric field provider, whereas in a DSSC, the semiconductor is used mainly for charge transport & the photo electrons are supplied by a different source(dye).
• DSSCs work even in low-light conditions. Hence they are very popular under cloudy weather conditions and non-direct sunlight, where traditional cells would be a failure. The cutoff in DSSC is so low they have been proposed for indoor usage, to collect energy for small devices from the lights in houses.
• A traditional solar cell is encased in glass with a metal at back for increasing its strength. Such setup may cause a decrease in its efficiency, as the cells heat up internally. However DSSCs are built up with only a thin layer of conductive plastic on the front side to allow radiation of heat much easily & quickly and therefore operate at low internal temperatures. Also the cell’s mechanical structure is such that it indirectly leads to higher efficiencies in higher temperatures.

DISADVANTAGES

• DSSCs are not considered as an option, for large-scale deployments where higher-cost higher-efficiency cells are more viable.DSCC is not manufactured in commercial scale yet.The sharp cut in silicon solar panels costs have led other types of solar technology like Solar Thermal and Thin Film Technology taking a back seat.
• One of the major concerns in a dye sensitized solar cell design is the use of the liquid electrolyte, which is not very stable at varying temperatures. The electrolyte can freeze at low temperatures cutting power production and causing physical damage. Sealing the panels becomes a difficult task, when the liquid expands at higher temperatures.
• Another major drawback is the electrolyte solution, which contains volatile organic solvents and must be carefully sealed. Replacing the liquid electrolyte with a solid has been a major ongoing field of research.

Read more about the Most Efficient Solar Cells .