Tuning the auxiliary donor in D–D–π–A photosensitizers to enhance DSSC photovoltaic performance: a DFT/TDDFT study

Harvesting solar energy from sunlight to generate electricity is considered one of the most important technologies to address future sustainability. Dye-sensitized solar cells (DSSCs) have attracted tremendous interest and attention over the past two decades due to their potential advantages for being implemented on large areas and using light-weight flexible substrates. The electronic, optical, and photovoltaic properties of dyes are pivotal for efficient solar energy conversion, and these properties can be finely tuned by structural modifications. In this study, we have designed a series of D-D-π-A architectured dyes, employing coumarin-thiophene-cyanoacrylic acid as the D-π-A core with the integration of eight efficient auxiliary donor units. Density functional theory (DFT) and time-dependent DFT (TD-DFT) computations have been employed to elucidate the electronic structure and optical characteristics of the dyes. Through DFT and TD-DFT simulations, we investigate the impact of various auxiliary donors on geometrical configurations, electronic structures, and optical properties. Our findings reveal that the incorporation of double donors not only enhances electron-donating capabilities but also impedes aggregation between dye molecules, thereby preventing recombination of injected electrons with the I^-/I₃ ^- in the electrolyte at TiO₂ semiconducting surfaces. This study underscores the effectiveness of incorporating auxiliary donor groups into organic dyes as a promising strategy for the development of high-performance, metal-free organic dyes tailored for photovoltaic applications.