Effective dyes for DSSCs–Important experimental and calculated parameters

This review article gives a short overview of the basic principle and criteria to evaluate the performance of dye-sensitized solar cells. Experimental measurements such as the short-circuit current density, open-circuit photovoltage, fill factor, energy conversion efficiency, light harvesting energy and band gap, are discussed and formulas to measure them are provided. In addition, density functional theory calculated parameters often used to evaluate dyes for dye-sensitized solar cells are explained and formulated. These include light harvesting energy, oscillator strength, injection driving force, regeneration driving force, driving force for charge recombination, excited state lifetime, the character (e.g. metal based, ligand based, π, π* etc.) and energy of the highest occupied and lowest unoccupied molecular orbital, natural transition orbitals, band gap and reorganization energy for electron and hole. The relationship between the density functional theory calculated and experimentally measured parameters is explained. An enhanced short-circuit current density and improved performance of dye-sensitized solar cells are anticipated with higher calculated values for light harvesting efficiency, driving force for electron injection and regeneration, and lower calculated values of reorganization energy. Additionally, higher calculated values of the dipole moment of the dye perpendicular to the TiO2 semiconductor surface are expected to enhance the open-circuit photovoltage, consequently contributing to the overall performance of dye-sensitized solar cells. Figures to illustrate the different measurable parameters and selected examples from the literature are provided. These techniques can be employed in subsequent experimental and theoretical studies to validate potential new dyes for use in dye-sensitized solar cells.