Biswas Abul Kalam, Das Amitava, Ganguly Bishwajit
Computation and Simulation Unit (Analytical Discipline and Centralized Instrument Facility), CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar-364002, India.
Academy of Scientific and Innovative Research, CSIR-National Chemical Laboratory, Pune-411008, India.
Phys Chem Chem Phys. 2015 Dec 14;17(46):31093-100. doi: 10.1039/c5cp05144d.
The power conversion efficiency of metal-free organic dyes in dye-sensitized solar cells (DSSCs) is now comparable to ruthenium-based polypyridyl and zinc-based porphyrin dyes. We have computationally investigated the structural, electronic and optical properties of a series of metal free organic dyes and their corresponding silicon substituted dyes. The DFT and TD-DFT calculations revealed that silicon substituted organic dyes have higher efficiency than the corresponding silicon free organic dyes. The computational results showed that the presence of silole units as a spacer group can significantly affect the performance of DSSCs compared to typically using thiophene as a spacer unit. These results corroborate the experimental observations reported in the literature. The time-dependent density functional theory (TDDFT) calculations performed at the CPCM–CAM-B3LYP/6-31+G* level of theory showed better agreement with the experimental absorption spectra of some reported metal free organic dyes having silole in the spacer group compared to other functionals and are employed in this study. Indoline donor based dye 5 showed a much shorter absorption spectrum (absorption peak at 425 nm) and smaller electron injection driving force (ΔGinjection = -1.77 eV) than the corresponding dye 8 containing silicon substituted indoline as a donor and a silole group as a spacer unit. λmax = 502 nm and ΔGinjection = -1.82 eV calculated for dye 8 are much larger than the corresponding silicon free dye 5. The silicon based dye 8 helps in achieving a much lower ΔGregeneration value than 5, which can facilitate the faster electron injection rate from the dye to the semiconductor TiO2. Dye 8 should also have a higher Voc value compared to other dyes (5-7) due to favourable interaction with the electrolyte (I(-)/I3(-)). The higher planarity and better conjugation in dye 8 facilitate the transfer of electrons from the dye molecules to the semiconductor TiO2. The calculations performed with phenyl protecting groups near the silicon center of the dye molecule 8 to diminish the dimerization process showed very similar optical properties as obtained with the corresponding unprotected dye system. The designed julolidine and pyrrolo-indolizine donor based dyes also showed a similar trend as observed for indoline donor based dyes.
染料敏化太阳能电池（DSSC）中无金属有机染料的功率转换效率现已与钌基多吡啶和锌基卟啉染料相当。我们通过计算研究了一系列无金属有机染料及其相应的硅取代染料的结构、电子和光学性质。密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算表明，硅取代有机染料比相应的无硅有机染料具有更高的效率。计算结果表明，与通常使用噻吩作为间隔单元相比，硅杂环戊二烯单元作为间隔基团的存在会显著影响DSSC的性能。这些结果证实了文献中报道的实验观察结果。在CPCM–CAM-B3LYP/6-31+G*理论水平上进行的含时密度泛函理论（TDDFT）计算表明，与其他泛函相比，其与文献中报道的一些间隔基团中含有硅杂环戊二烯的无金属有机染料的实验吸收光谱吻合得更好，本研究采用了该理论。与相应的以硅取代吲哚啉为供体、硅杂环戊二烯基团为间隔单元的染料8相比，基于吲哚啉供体的染料5的吸收光谱要短得多（吸收峰在425 nm），电子注入驱动力也更小（ΔGinjection = -1.77 eV）。染料8的计算值λmax = 502 nm和ΔGinjection = -1.82 eV比相应的无硅染料5大得多。基于硅的染料8有助于实现比染料5低得多的ΔGregeneration值，这可以促进从染料到半导体TiO2的更快电子注入速率。由于与电解质（I(-)/I3(-)）的有利相互作用，染料8与其他染料（5 - 7）相比也应具有更高的开路电压（Voc）值。染料8中更高的平面性和更好的共轭性有助于电子从染料分子转移到半导体TiO2。在染料分子8的硅中心附近使用苯基保护基团以减少二聚化过程的计算显示，其光学性质与相应的未保护染料体系非常相似。设计的基于久洛里定和吡咯并吲哚嗪供体的染料也显示出与基于吲哚啉供体的染料类似的趋势。
