Dye-Sensitized Solar Cells

Introduction

The photosensitizers absorb photons and have a wide spectral absorption range, which is an important part of the dye-sensitized solar cells (DSSCs) and directly affects the energy conversion efficiency of the cell. DSSCs combine the advantages of photosensitizers and inorganic semiconductors, have a wide spectral response range, simple manufacturing process, low cost, environmental friendliness, and broad application prospects, so they have attracted people's attention.

Figure 1. The dye-sensitized solar cells

Requirements for Photosensitizer

A photosensitizer is considered efficient for DSSCs when it fulfills these requirements:

a) The absorption spectrum of the photosensitizers should cover the whole visible region and even the part of the near-infrared.

b) The photosensitizers should have anchoring groups (-COOH, -H₂PO₃, -SO₃H, etc.) to strongly bind the dye onto the semiconductor surface.

c) For n-type DSSCs, the excited state level of the photosensitizer should be higher in energy than the conduction band edge of n-type semiconductor, so that an efficient electron transfer process between the excited dye and conduction band of the semiconductor can take place. In contrast, for p-type DSSCs, the HOMO level of the photosensitizers should be at more positive potential than the valene band level of p-type semiconductor.

d) For dye regeneration, the oxidized state level of the photosensitizer must be more positive than the redox potential of electrolyte.

e) The photosensitizers should be photostable, electrochemical and thermal stability are also required.

Mechanism

In generally, an exciton (e-h pair) is produced after photon absorption by the dye molecule, which moves toward the conduction band (CB) of TiO₂ and the conductive substrate. Then, an electron is transferred through the external load to the counter electrode, reduces the electrolyte (I⁻/I³⁻), and regenerates the dye.^[1]

Figure 2. Schematic illustration of the basic mechanism of DSSCs.

What Can Alfa Chemistry Do?

Alfa Chemistry's technical R&D team has focused on the preparation and application of photosensitizers for many years, which has established long-term cooperative relationships with many well-known enterprises and research institutions. We have conducted research on various problems encountered by DSSCs, which can select the appropriate solution according to the customer's experimental purpose. The DSSCs technologies we provide are as follows:

• We can provide various electrochemical measurements, including cyclic voltammetry, differential pulse voltammetry, square wave voltammetry, electrochemical impedance spectroscopy, and spectroelectrochemistry.
• We can provide various photoelectrochemical measurements, including electron transport measurements, electron lifetime measurements, electron concentration measurements, electron quasi-fermi level measurements, charge collection efficiency and diffusion length, and photoinduced absorption spectroscopy.
• We also can provide the module designs and develop solution according to customer needs.

Reference

• Grätzel M. Dye-sensitized solar cells. J. Photoch. Photobio. C, 2003, 4(2): 145-153.