Tu Wei Han, Tan Yi Yin, Rege Omkar, Manzhos Sergei
Anderson Junior College, 4500 Ang Mo Kio Avenue 6, Singapore, 569843, Singapore,
J Mol Model. 2015 Apr;21(4):67. doi: 10.1007/s00894-015-2624-2. Epub 2015 Mar 7.
We present a computational density functional theory study of the potential to improve the solar absorbance of small organic dyes featuring a phenothiazine donor and an acceptor moiety that combines a thiophene unit and a cyanoacrylic group. We consider different conjugation orders and functional groups on and around the thiophene unit, including electron-donating and electron-withdrawing moieties (H, F, CH3, CF3, and CN). We predict that by combining change of conjugation order and functionalization with electron withdrawing CN groups, it must be possible to decrease the excitation energy by up to 60 % vs. the parent dye (which would correspond to a redshift of the absorption peak maximum from 450 nm to 726 nm), effectively enabling red light absorption with small dyes. The contraction of the band gap is mostly due to the stabilization of the LUMO (by up to 1.8 eV), so that-in spite of the kinetic redundancy of the parent dye with respect to the conduction-band minimum of TiO2-care must be taken to ensure efficient injection when using the dyes in dye-sensitized solar cells. By studying 50 dyes, of which 44 are new dyes that are studied for the first time in this work, we identify parameters (such as charges, dihedral angles between donor and acceptor groups, bond length alternation) which can serve as predictors of the band gap. We find that bond length alternation or dihedral angles are not good predictors, while the charge on the thiophene unit is.
我们开展了一项计算密度泛函理论研究，旨在探究改善一类小型有机染料太阳能吸收率的潜力。这类染料以吩噻嗪为供体，其受体部分结合了噻吩单元和氰基丙烯酸基团。我们考虑了噻吩单元上及其周围不同的共轭顺序和官能团，包括供电子和吸电子基团（氢、氟、甲基、三氟甲基和氰基）。我们预测，通过结合共轭顺序的改变以及用吸电子的氰基进行官能化，与母体染料相比，激发能有可能降低多达60%（这将对应于吸收峰最大值从450纳米红移至726纳米），从而有效地使小型染料能够吸收红光。带隙的缩小主要归因于最低未占分子轨道的稳定化（高达1.8电子伏特），因此，尽管母体染料相对于二氧化钛的导带最小值在动力学上存在冗余，但在染料敏化太阳能电池中使用这些染料时，仍必须注意确保有效的注入。通过研究50种染料，其中44种是在本工作中首次研究的新染料，我们确定了一些参数（如电荷、供体和受体基团之间的二面角、键长交替），这些参数可作为带隙的预测指标。我们发现键长交替或二面角不是很好的预测指标，而噻吩单元上的电荷是。
