Deep eutectic solvent based on choline chloride and phenol as electrolyte additives in dye-sensitized solar cells: a comparison with 4-tert-butylpyridine

The electrolyte additives are used in dye-sensitized solar cells to improve the photovoltaic performance of the devices, but they still remain their problems on the long-term stability of the solar cells and chemical safety. We have studied the use of two deep eutectic compounds based on choline chloride and phenol with two ratios of 1:2 and 1:3 as alternative electrolyte additives. These compounds own their advantages as eco-friendly chemicals, low cost, and simple synthesis process even at a large amount production. The two compounds, in comparison with the popular additive 4-tert-butylpyridine (4-TBP), were implemented in the functional devices which were characterized by current–voltage measurement and electrochemical impedance spectroscopy. Results showed that the two new additives could improve open circuit voltage values about 10–40 mV, whereas about 100 mV for 4-TBP, compared to the case without additives. Furthermore, using these new additives could result in a higher the short circuit current (J_sc) which was not observed with 4-TBP. These phenomena were explained by the shielding effects and charge transfer processes at the interfaces of electrodes and electrolyte. This study helped to design new efficient and eco-friendly additives for dye-sensitized solar cells in future scale-up production and commercialization.