Rational Design of Low-Band Gap Star-Shaped Molecules With 2,4,6-Triphenyl-1,3,5-triazine as Core and Diketopyrrolopyrrole Derivatives as Arms for Organic Solar Cells Applications.

Xinhao Zhang,Ruifa Jin

doi:10.3389/fchem.2019.00122

Abstract

A series of D–A novel star-shaped molecules with 2,4,6-triphenyl-1,3,5-triazine (TPTA) as core, diketopyrrolo[3,4-c]pyrrole (DPP) derivatives as arms, and triphenylamine (TPA) derivatives as end groups have been systematically investigated for organic solar cells (OSCs) applications. The electronic, optical, and charge transport properties were studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches. The parameters such as energetic driving force ΔEL−L, adiabatic ionization potential AIP, and adiabatic electron affinity AEA were also calculated at the same level. The calculated results show that the introduction of different groups to the side of DPP backbones in the star-shaped molecules can tune the frontier molecular orbitals (FMOs) energy of the designed molecules. The designed molecules can provide match well with those of typical acceptors PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester). Additionally, the absorption wavelengths of the designed molecules show bathochromic shifts compared with that of the original molecule, respectively. The introduction of different groups can extend the absorption spectrum toward longer wavelengths, which is beneficial to harvest more sunlight. The calculated reorganization energies suggest that the designed molecules are expected to be the promising candidates for ambipolar charge transport materials except molecule with benzo[c]isothiazole group can be used as hole and electron transport material. Moreover, the different substituent groups do not significantly affect the stability of the designed molecules.

Highlights

Nowadays, organic π-conjugated small molecules (SMs) used as the donors in organic solar cells (OSCs) have drawn intense attention because of their outstanding advantages, such as excellent reproducibility, easy purification, well-defined chemical and optoelectronic properties (Coughlin et al, 2014; Yao et al, 2016; Bin et al, 2017)
The star-shaped D–A type DPP-based molecules may possess narrower band gap, broader absorption region, strong light absorption, and high charge carrier mobility (Sharma et al, 2014; Shiau et al, 2015). Considering these merits and characteristics mentioned above, in this contribution, we report the design of a series of novel star-shaped DPP-based molecules with electronaccepting 2,4,6-triphenyl-1,3,5-triazine (TPTA) as core, electron accepting DPP derivatives as arms, and electron-donating triphenylamine derivatives (TPA) as end groups for OSCs applications
In order to characterize the optical and electronic properties, we investigated the distributions of the frontier molecular orbitals (FMOs) for the designed molecules

Summary

Introduction

Organic π-conjugated small molecules (SMs) used as the donors in organic solar cells (OSCs) have drawn intense attention because of their outstanding advantages, such as excellent reproducibility, easy purification, well-defined chemical and optoelectronic properties (Coughlin et al, 2014; Yao et al, 2016; Bin et al, 2017). The high-efficiency SMs donor materials should possess suitable frontier molecular orbital (FMOs) (including the highest occupied molecular orbital, HOMO, and lowest unoccupied molecular orbital, LUMO) energy levels, high charge carrier mobility, broad absorption region, and miscibility with fullerene derivatives. In this regard, the HOMO level of the designed donor materials should been reduced to increase the open circuit voltage (Voc), because the HOMO of donor and the LUMO of acceptor are closely relate to the Voc. With the aim to harvest more sunlight, the energy gaps of the designed donor materials should been decreased, which results in an increase in the short circuit current density (Jsc) (Loser et al, 2017; Maglione et al, 2017; Zhang et al, 2017).

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Results

Conclusion