Abstract
In this work, we study the light absorption properties of different novel molecules based on benzo[1,2-b:4,5-b′]dithiophene (BDT), namely, BT-2F, BTRCl, and BTTzR, which hold great promise as electron-donor materials in organic solar cells. By employing density functional theory, we study the electronic states and related transitions in these systems. Moreover, in the case of BTTzR, we observe that the addition of two and three oligothiophene chains to the central benzene ring of the BDT unit leads to both a red-shift of the existing peaks and, interestingly, the development of new blue-shifted features, an effect that permits to enhance the panchromaticity of the molecule in the visible spectral range, thus rendering these new derivatives highly appealing as light absorbers in organic solar cells.
Highlights
Together with other materials exhibiting high photovoltaic ability, such as metal-halide perovskites,1–5 semiconducting polymers,6,7 quantum dots,8,9 and carbon nanotubes,10,11 small molecules are widely studied in the solar cell research community
The authors reported excellent photovoltaic performance and power conversion efficiency as high as 7.38% under AM 1.5G irradiation (100 mW cm−2). They attributed the excellent photovoltaic performance to the high mobilities and broadband absorption with relatively high oscillator strength owing to the efficient conjugation in the backbone structure and intramolecular charge transfer (ICT) between the terminal acceptor units and the central donor building block (BDT)
We have studied the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of BTTzR, BTTzv2, and BTTzRv3, highlighting that such orbitals, in particular the HOMO orbital, are significantly delocalized over the oligothiophene pendants in BTTzRv3
Summary
Together with other materials exhibiting high photovoltaic ability, such as metal-halide perovskites, semiconducting polymers, quantum dots, and carbon nanotubes, small molecules are widely studied in the solar cell research community. They attributed the excellent photovoltaic performance to the high mobilities and broadband absorption with relatively high oscillator strength owing to the efficient conjugation in the backbone structure and intramolecular charge transfer (ICT) between the terminal acceptor units (octyl cyanoacetate and 3-ethylrhodanine) and the central donor building block (BDT) Following this seminal study, in 2020, a novel small molecule donor, BTTzR, was developed, and an all-small-molecule solar cell employing BTTzR as the electron-donor showed an impressive power conversion efficiency (PCE) of 13.9%.24. In 2020, a novel small molecule donor, BTTzR, was developed, and an all-small-molecule solar cell employing BTTzR as the electron-donor showed an impressive power conversion efficiency (PCE) of 13.9%.24 Such a high-efficiency was achieved thanks to the strong absorption in the wavelength range of 400–650 nm, as well as a wide optical bandgap of 1.88 eV, a low-lying highest occupied molecular orbital (HOMO) energy level scitation.org/journal/adv of −5.58 eV, and an ordered molecular orientation and packing. These results demonstrate that panchromaticity, i.e., the capability to absorb light in the whole visible range, is one of the key parameters necessary to achieve high PCEs
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