Ashassi-Sorkhabi Habib, Salehi-Abar Parvin
Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz Tabriz Iran
RSC Adv. 2018 May 18;8(33):18234-18242. doi: 10.1039/c8ra01879k. eCollection 2018 May 17.
Density functional theory (DFT) was used to investigate the electronic and optical properties of the , , and derivatives of 2,2',7,7'-tetrakis-(,-di-4-methoxyphenylamino)-9,9'spirobifluorene (spiro-OMeTAD) and its two oxidized forms (+1 and +2). The energy level, distribution shape, and density of highest occupied molecular orbital (HOMO) and of lowest unoccupied molecular orbital (LUMO) were computed for all three derivatives and compared in the neutral and oxidized forms. Results indicated that the different positions of OMe in the spiro-OMeTAD framework lead to different optical properties. It was also found that compared to the neutral form, in the oxidized forms, the maximum absorption band red shifts, new signals in the visible range between 500 and 850 nm appear, and the Stokes shift values reduce for all three derivatives. The exciton binding energy of spiro-OMeTAD with an -OMe substituent is 0.52 eV, being smaller than that of -OMe and -OMe, indicating easier generation of free charge carriers. The hole mobility was calculated for all three molecules, and the obtained data revealed that the hole mobility of the -OMe substituent has a value of 7.90 × 10 cm V s, which is respectively 3 and 11 times larger than that of -OMe and -OMe. The smaller exciton binding energy and larger hole mobility of the -OMe substituent will result in a higher short-circuit current density ( ) and a higher fill factor, respectively, demonstrating that -spiro-OMeTAD is a promising candidate for use in perovskite solar cells. The reorganization energy, electron affinity, and ionization potential were also calculated and discussed.
采用密度泛函理论（DFT）研究了2,2',7,7'-四（N,N-二-4-甲氧基苯基氨基）-9,9'-螺二芴（spiro-OMeTAD）及其两种氧化态（+1和+2）的衍生物的电子和光学性质。计算了所有三种衍生物在中性和氧化态下的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）的能级、分布形状和密度，并进行了比较。结果表明，spiro-OMeTAD骨架中OMe的不同位置导致不同的光学性质。还发现，与中性态相比，在氧化态下，所有三种衍生物的最大吸收带红移，在500至850 nm的可见光范围内出现新信号，斯托克斯位移值减小。带有-N-OMe取代基的spiro-OMeTAD的激子结合能为0.52 eV，小于-O-OMe和-S-OMe的激子结合能，表明更容易产生自由电荷载流子。计算了所有三种分子的空穴迁移率，所得数据表明，-N-OMe取代基的空穴迁移率值为7.90×10⁻³ cm² V⁻¹ s⁻¹，分别比-O-OMe和-S-OMe的空穴迁移率大3倍和11倍。-N-OMe取代基较小的激子结合能和较大的空穴迁移率将分别导致更高的短路电流密度（Jsc）和更高的填充因子，表明-N-spiro-OMeTAD是用于钙钛矿太阳能电池的有前途的候选材料。还计算并讨论了重组能、电子亲和能和电离势。
