Exploring the effect of cyclic-functionalized boron-dipyrromethene on the optoelectronic and nonlinear optical properties of coumarin donor-Based D-Π-A dyes for dye-sensitized solar cells: a DFT/TD-DFT approach

Abstract Coumarin and its derivatives have been widely studied as a photosensitizer for dye-sensitized solar cells (DSSC) with encouraging results. However, its use in such a device is limited by its low spectral response in the red band and near-infrared. In this study, we used boron-dipyrromethene (BODIPY) as well as BODIPY functionalized with a homocycle (cyclopentadiene) or heterocycles (pyrrole, furan, and thiophene) as π -spacers to design five D- π -A type dyes (CB0 to CB4) based on the NKX−2700 dye. The optoelectronic, nonlinear optical (NLO), and intramolecular charge transfer (ICT) properties were studied in detail at the MN15 theory level combined with the 6-31 G(d,p) basis set. The study aims to demonstrate the effectiveness of cyclic compound-functionalized BODIPY in overcoming these defects in D- π -A dye systems used in DSSCs. Theoretical results reveal that fusing BODIPY with cyclic compounds as π -conjugated spacers is an excellent strategy to enhance the optoelectronic and ICT properties of D- π -A dye systems. This improvement leads to an excellent light-harvesting efficiency (LHE) with a broader spectral response range (350–1000 nm), lower excitation energy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ex</mml:mi> </mml:mrow> </mml:msub> </mml:math> ), smaller bandgap ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">gap</mml:mi> </mml:mrow> </mml:msub> </mml:math> ), higher molar extinction coefficient, and the lowest reorganization energy ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">total</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) compared to the reference dye NKX-2700. These factors may contribute to a higher short-circuit current ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>J</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">SC</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) in DSSCs. The NLO property analysis suggests that the CB3 dye could offer better light interaction, which is crucial for optimizing DSSC performance. This study provides new ideas for the synthesis of highly efficient metal-free organic dyes for DSSCs.