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Effects of thiophene substituents on hole-transporting properties of dipolar chromophores for perovskite solar cells

Cui, Jianyu, Rao, Wei, Hu, Weixia, Zhang, Zemin, Shen, Wei, Li, Ming, He, Rongxing
Journal of materials science 2018 v.53 no.9 pp. 6626-6636
absorption, electrochemistry, photovoltaic cells, spectral analysis, thiophene, wavelengths
We present a theoretical investigation of thiophene substituent effects on the electrochemical properties of dipolar chromophores (TCNE, TCNE22 and TCNE24) as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). Herein, the material properties in crystalline phases are explored by using the first-principle calculations combined with Marcus theory. The results show that the increased number of thiophene substituents for TCNE, TCNE22 and TCNE24 results in a redshift of the absorption spectrum (27–46 nm). Furthermore, both TCNE22 and TCNE24 have maximum absorption peaks at a wavelength of 400 nm. Most importantly, the molecular planarity is improved effectively, which generates strong intermolecular face-to-face π–π packing interaction. The higher hole mobility of TCNE24 (2.069 × 10⁻¹ cm² V⁻¹ s⁻¹) with four thiophene substituents is obtained due to the face-to-face π–π packing. The new designed TCNE24 not only has excellent spectral property, but also has strong hole mobility. Therefore, TCNE24 is a promising organic small-molecule HTMs. Our work provides theoretical guidance for designing higher-performance HTMs in PSCs.