Abstract
Due to their low cost, facile fabrication, and high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have attracted much attention. Ruthenium (Ru) complex dyes and organic solvent-based electrolytes are typically used in high-efficiency DSSCs. However, Ru dyes are expensive and require a complex synthesis process. Organic solvents are toxic, environmentally hazardous, and explosive, and can cause leakage problems due to their low surface tension. This review summarizes and discusses previous works to replace them with natural dyes and water-based electrolytes to fabricate low-cost, safe, biocompatible, and environmentally friendly DSSCs. Although the performance of “eco-friendly DSSCs” remains less than 1%, continuous efforts to improve the PCE can accelerate the development of more practical devices, such as designing novel redox couples and photosensitizers, interfacial engineering of photoanodes and electrolytes, and biomimetic approaches inspired by natural systems.
Highlights
To develop eco-friendly dyesensitized solar cells (DSSCs), efforts to replace organic electrolytes with aqueous electrolytes have progressed for several years (Table 4)
The relatively poor performance of DSSCs using aqueous electrolytes compared to organic electrolytes can be attributed to various causes: (1) less wettability of the photoanode surface [104,107,108,112]; (2) desorption of the dye from the surface of the semiconductor [89,118,119,120]; (3) reduction in the diffusion coefficient [89,104,107,108,112]; (4) recombination derived from a higher concentration of free iodine [91,121]; and (5) negative shift of the conduction band [122,123,124]
Bella et al used the TiCl4 treatment, which improved the power conversion efficiency (PCE) of DSSCs based on an aqueous electrolyte comprising NaI and I2 from 1.25% to 2.37% (Figure 5b) [116]
Summary
For high-efficiency DSSCs, Ru-complex dyes and organic solvent-based electrolytes are typically used. Ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP) are used due to their low vapor pressure and volatility. Such organic solvents are not the best choice in terms of safety [19]. Ru-complex dyes absorb a wide range of absorption wavelength from 300 nm to 600 nm in visible light, resulting in high-efficiency DSSCs with the maximum efficiency of. The typical components in DSSCs, organic solvents, and Ru-based complex dyes may need to be replaced to realize low cost, biocompatible, and environmentally benign devices. Water and natural dyes derived from plants could be excellent alternatives
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