**2.1 Dye sensitized solar cells**

Dye-sensitive solar cell technologies continue to be the focus of scientific and industrial research as one of the photovoltaic devices that provide the opportunity to benefit from the sun, which is one of the renewable energy sources. The DSSC projects are widely oriented toward increasing power generation and low-cost generation. The numerous critical processes for DSSC power production mainly occur at the nanocrystal/dye/electrolyte interface (see **Figure 7**), which is now a significant research focus in this field. The maximum efficiency (14.3%) [51] has been obtained using a ruthenium complex in combination with an electrolyte [52, 53]. However, the limited supply of ruthenium and volatile organic solvents are a significant concern for the long-term stable operation of DSSCs. Due to their ideal properties of minimal

#### *Investigation of Boron-Based Ionic Liquids for Energy Applications DOI: http://dx.doi.org/10.5772/intechopen.105970*

vapor pressures, high conductivity, and thermal stability, RTILs have emerged as a possible choice for enhancing the efficiency of DSSCs. ILs-based DSSCs with ruthenium complexes as sensitizers have already demonstrated impressive photovoltaic performance and stability.

The properties of ILs make them appropriate for use in perovskite solar cells to address significant device efficiency and stability issues, as in DSSC. It was proposed that ILs form a protective layer on the perovskite film to provide the device with moisture and thermal stability. However, no extensive research on boron-containing ILs used in perovskite solar cell technology has been conducted [54, 57]. The DSSC conversion efficiency still lags behind that of organic solvent-containing DSSCs. The fundamental cause of this poor performance is the ILs' high viscosity, which results in mass transfer constraints on the photocurrent under sunlight. To overcome this problem, it uses a combination of a low viscosity IL and a redox-active salt as the electrolyte to optimize the diffusion rate of the redox couple. These additives optimize the kinetics of the processes of electron injection that occur at the photoanode. The nature of IL, especially basic anions such as dicyanamide, can significantly affect the position of the conduction band edge and thus the open-circuit voltage (Voc) of the device. The most efficient IL-based system reported to date employs the I− / I3 − redox couple in conjunction with one of a eutectic solution of imidazolium iodide salts [C2mim], yielding good stability [B(CN)4] − [53–56, 58]. According to research, when combined with titania/electrolyte in DSSCs, [B(CN)4] exhibits a higher photocurrent response. [B(CN)4] − anions cause a downward displacement of an electrolyteimmersed film's conduction-band edge, resulting in a more favorable energy balance at the titania/dye interface and thus a better exciton dissociation efficiency [53].

Organic dye-sensitized [B(CN)4] − IL-based solar cells were reported by Daibin Kuang et al [55]. It has been claimed that the first rapor and organic DSSC combined with these newly developed ILs (without solvent) obtained a conversion efficiency of 7.2% to electrical power. A molecularly tailored indoline sensitizer with 1-ethyl-3-methyl-imidazolium tetracyanoborate ([EMIB (CN)4]) was used in the electrolyte. This is the first time an ionic-liquid electrolyte has been used to achieve such high efficiency for organic dye-based ILs.

Magdalena Marszalek et al. [56] prepared and characterized the [B(CN)4] − anionbased series of ILs for use in DSSC applications. These new fluorous-free ILs were composed of [B(CN)4] − anions and cations such as imidazolium and ammonium. Synthesized and characterized novel BBILs were evaluated as electrolyte additives in DSSC, with obtained efficiencies of 7.35 and 7.85% under 100 and 10% sun, respectively, in combination with the standard Z907 dye [56].

Promising alternative electrode materials with BBILs may include nanostructures that may have lower charge transfer resistance for I− /I3 − relative to a molecular solvent in an IL electrolyte. However, reducing the charge transfer resistance to obtain acceptable performance under full solar radiation is extremely important for device development, and this field of study remains open to considerable advancement.
