Dye-sensitized solar cells (DSSC) are mainly composed of nanoporous semiconductor films, dye sensitizers, electrolytes, counter electrodes and conductive substrates. In this, the electrolyte is located between the photoanode and the counter electrode, which undertakes the roles of dye regeneration and hole transport. According to the different states of electrolytes, it can be divided into liquid electrolytes, quasi-solid electrolytes and solid electrolytes. In electrolytes, redox couples are very important for the stability of DSSC. In the process of dye regeneration, redox couples are mainly responsible for the charge transport between the photoanode and the counter electrode. In addition, the performance stability, maximum photoelectric conversion efficiency, and open-circuit voltage of DSSC are all related to the composition of the electrolyte and the mass transport process of charge carrier diffusion in the electrolyte. It can be seen that the electrolyte has a great influence on the performance of DSSC. Electrolytes with excellent performance can enhance the stability, light harvesting efficiency and electron injection efficiency of DSSC devices, and promote the thin film, light weight and flexibility of DSSC devices.
Figure 1. Electrolytes in DSSC devices
- Liquid DSSC: The electrolyte used in the liquid DSSC device is a liquid electrolyte. Depending on the solvent used, liquid electrolytes can be divided into organic liquid electrolytes and ionic liquid electrolytes. In liquid electrolytes, the solvent is the most basic component, providing an environment for active ions to dissolve and diffuse. Common organic solvents in organic liquid electrolytes are nitriles (such as acetonitrile, valeronitrile, methoxypropionitrile), esters (such as ethylene carbonate, propylene carbonate, γ-butyrolactone). The DSSC device using ionic liquid as solvent shows good stability.
- Quasi-solid/solid-state DSSC: Quasi-solid and solid-state DSSC often use hole-conducting material (HTM) as the electrolyte. HTM used in solid-state dye batteries can be divided into P-type inorganic semiconductor materials and P-type organic semiconductor materials. In DSSC applications, HTM has the following requirements: (1) can transfer the holes generated by the oxidative dye; (2) can be deposited in the porous nanoparticle layer; (3) will not dissolve or degrade the dye; (4) transmittance in the visible spectral range. Such DSSC devices exhibit good stability and conversion efficiency, and have broad applications in the fabrication of inexpensive and flexible DSSC devices of different shapes and sizes.
- Haider Iftikhar, Gabriela Gava Sonai, Syed Ghufran Hashmi, Ana Flávia Nogueira, Peter David Lund. Progress on Electrolytes Development in Dye-Sensitized Solar Cells [J]. Materials, 2019, 12, 1988.