A Low‐Energy‐Gap Thienochrysenocarbazole Dye for Highly Efficient Mesoscopic Titania Solar Cells: Understanding the Excited State and Charge Carrier Dynamics

Abstract

Maintaining both a high external quantum efficiency and a large open-circuit photovoltage of dye-sensitized solar cells (DSSCs) is a crucial challenge in the process of developing narrow-energy-gap dyes for the capture of infrared solar photons. Herein, we report two donor-acceptor organic dyes, C294 and C295, with a polycyclic heteroaromatic unit, 6,11-dihydrothieno[3',2':8,9]chryseno[10,11,12,1-bcdefg]carbazole (TCC), as the central module of the electron donor, and ethylbenzothiadiazole-benzioc acid as the electron acceptor. The interfacial charge recombination was successfully mitigated by introducing an additional branched aliphatic chain in C295. Furthermore, the O⋅⋅⋅S nonbonding interaction between the oxygen atom of the alkoxy group and the sulfur atom of the thiophene in C295 controlled the conformation of C295, resulting in a narrow energy-gap. Time-resolved spectroscopic measurements on C294 and the model dye C272 indicated that the elevation of the HOMO energy level decreased the kinetics and yield of hole injection owing to a reduction in the driving force and that the shortened excited-state lifetime caused by the narrowing of the energy gap was unfavorable for electron injection. By fine tuning the composition of the electrolyte, C294 and C295 eventually achieved high power conversion efficiencies of 11.5 % and 12.4 %, respectively, under full sunlight of air mass 1.5 global conditions.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…In their further research on donor–acceptor organic dyes, Wang and co-workers reported two more molecules with a NAP-based unit as the central module of the electron donor and ethynylbenzothiadiazole-benzoic acid as the electron acceptor, C5.2a and C5.2b , along with the previously reported model dye C5.1 (Chart ). The thiophene-fused compounds C5.2a and C5.2b were more electron rich, corresponding to a higher HOMO energy and decreased HOMO–LUMO gap compared to C5.1 .…”

New insights into the alkoxy effects on auxiliary adsorption and inhibiting charge recombination in dye-sensitized solar cells with high open circuit voltage: a theoretical investigation

“…They assumed that the additional side chains in C295 can lead to a more compact and well-arranged molecular layer on the surface of the titania film, which hindered the recombination between electrons in titania and the oxidized species in the electrolyte and accounted for its higher V oc . 8 Zhang et al showed that when the hexyl group was replaced with the dodecyl group as shown in Fig. 1, the V oc increased from 1170 mV to 1240 mV.…”

Accelerated Discovery of Potential Organic Dyes for Dye‐Sensitized Solar Cells by Interpretable Machine Learning Models and Virtual Screening

“…Further improving the PCE of DSSCs requires design and synthesis of new high-efficiency organic dyes, which play a pivotal role in absorbing visible light and generating photocurrent. [9][10][11][12][13][14][15] However, the chemical space of possible organic dyes is extremely huge due to the vast number of functional groups and their various linkage combinations, and accordingly, the tedious and expensive trial-and-error experimental procedure becomes the bottleneck to find an optimal dye molecule from such a huge chemical space.…”