Dye-Sensitized Solar Cells

Abstract - A solar cell is a device that is used to convert solar energy into electricity. Semiconductor solar cells are made from two doped crystals, one n-type doped crystal, which has extra free electrons, and the other p-type doped crystal, which has extra holes. When the solar cell is placed in sunlight, photons from the sunlight can strike the bound electrons in the n-type semiconductor. This collision will give the electrons enough energy to be pushed out of the valence band through the band gap into the conduction band. In the conduction band, the electrons are free to move about the silicon. When the solar cell has a load placed across it, electrons will flow from the n-type side to the p-type side before returning to the n-type material, where the electron can once again combine with the valence band hole they left behind. In this way, sunlight creates an electrical current in the solar cell. [2]

INTRODUCTION

A major consideration when dealing with solar cells is the efficiency at which it converts the solar energy into electricity. Only photons with a certain energy level will enable the electrons to cross the band gap and contribute to producing an electric current. In the case of silicon, most of the visible light spectrum (from red to violet) has enough energy to produce a current. At the blue and violet end of the spectrum, the photons have more than enough energy to cross the band gap. Some of this energy is transferred into the electrons, but the vast majority of it is wasted as heat. [2]

The biggest issue with the standard approach to making a solar cell is the cost. Solar cells must have a thick layer of expensive doped silicon in order to capture photons at a useful rate. This also increases the chance that a newly released electron will run into a hole created by another freed electron and never reach the band gap. Many different approaches have been tried in an effort to reduce cost, but they have seen limited implementation due to a variety of issues. These reasons produce a maximum efficiency of standard silicon solar cells of around 12 to 15%. [2]

HISTORY

A dye-sensitized solar cell is low-cost thin film solar cell. The dye-sensitized solar cell was invented by Michael Grätzel and Brian O'Regan in Switzerland in 1991. This solar cell has a large upside because it is made from fairly inexpensive materials and does not require complicated machinery to be manufactured. When produced in large quantities, dye-sensitized solar cells should be significantly less expensive than previous versions of the solar cell. They can also be made into flexible sheets that are sturdier than previous solar cells. This would allow the solar cells to endure things, like hail or tree branches, which would have damaged previous solar cell designs. Dye-sensitized solar cells have smaller conversion efficiencies than the best thin film solar cells.