Bridge effect on the charge transfer and optoelectronic properties of triphenylamine-based organic dye sensitized solar cells: theoretical approach

In this work, a series of six organic dyes-sensitized solar cells (DSSCs) combining various pi-bridges with a fixed donor (triphenylamine) and a fixed electron acceptor (cyanoacrylic acid), namely D1-6, were studied. The geometrical structure, electronic and optical properties of these dyes have been investigated with the density functional theory and TD-BHandHLYP hybrid functional (time-dependent Becke-Half-and-Half-Lee-Yang-Parr's) methods. The effects of pi-bridging of the dyes have shown that the rings with a sulfur atom reduce the energy gaps and provide a redshift of the absorption spectra. Similarly, we focus on the description of the ground and excited state properties. On the other hand, the pyrrole group improves the open-circuit voltage (V-OC) and the light-harvesting efficiency parameters leading to greater power conversion efficiency. Furthermore, the results revealed lowest total reorganization energy lambda (lambda(+) and lambda(-)) for the dye D3 with pyrrole linkage, which reflects its most favorable charge-transport properties, implying a lower charge recombination rate, faster charge injection and dye regeneration processes. Therefore, this study would provide a new path to design novel conjugated organic molecules as dyes for high-performance DSSCs.