Graphene, a promising two-dimensional carbon material, has been extensively employed in dye-sensitized solar cells (DSSCs) with encouraging results. However, how graphene improves the power conversion efficiency is still unclear. In this research, a series of dyes with pristine, doped and hole graphene based on the dye WS5 were designed and systematically investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT), aimed at revealing the effect of these functionalized graphenes on photophysical properties. The results based on the absorption properties reveal that introducing functionalized graphene not only enhances absorption intensity, but also expands the absorption spectrum, which will lead to a better photocurrent response. According to an analysis of the intermolecular interaction between dye and I₂, all the designed dyes possess a slow electron recombination rate, except WS5-HoS, and then possibly an increasing V_OC. Additionally, J_ph increases steadily as the electronegativity of the doped atoms (C, Si and Ge) in graphene increases. The dyes with the insertion of short functionalized graphene exhibit a superior performance in J_ph to that of long functionalized graphene. Meanwhile, using graphene to decorate the dye WS5 could adjust energy levels to narrow the energy gap. Dyes with short functionalized graphene exhibit the smallest HOMO–LUMO gaps, followed by long functionalized graphene and the dye WS5. With the enhancement in the electronegativity of doped atoms (C, Si and Ge) in graphene, the energy gap decreases steadily. Inserting functionalized graphene facilitates electron transfer properties due to lower aromaticities, especially for dyes with short functionalized graphene. Taken all together, the introduction of short functionalized graphene in a dye is a valid approach to increase overall efficiency, especially for graphene doped with atoms of larger electronegativity, so the photophysical properties of DSSCs could be boosted in the future.

中文翻译：

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关于原始，掺杂和空穴石墨烯对染料敏化太阳能电池整体性能影响的理论见解†

石墨烯是一种有前途的二维碳材料，已被广泛用于染料敏化太阳能电池（DSSC）中，并取得了令人鼓舞的结果。然而，石墨烯如何提高功率转换效率仍不清楚。在这项研究中，设计了一系列基于染料WS5的原始，掺杂和空穴石墨烯的染料，并通过密度泛函理论（DFT）和时变DFT（TD-DFT）进行了系统研究，旨在揭示这些染料的效果。功能化石墨烯对光物理性质的影响。基于吸收特性的结果表明，引入官能化的石墨烯不仅增强了吸收强度，而且扩展了吸收光谱，这将导致更好的光电流响应。根据对染料与I之间分子间相互作用的分析₂，所有的设计染料具有缓慢的电子的复合率，除了WS5-HOS，然后可能增加V _OC。另外，随着石墨烯中掺杂原子（C，Si和Ge）的电负性增加， J _ph稳定增加。插入短官能化石墨烯的染料在J _ph中表现出优异的性能到长功能化石墨烯。同时，使用石墨烯装饰染料WS5可以调节能级以缩小能隙。短功能化石墨烯的染料具有最小的HOMO-LUMO间隙，其次是长功能化石墨烯和染料WS5。随着石墨烯中掺杂原子（C，Si和Ge）的电负性增强，能隙稳步减小。插入官能化的石墨烯由于较低的芳香性而促进了电子转移性能，特别是对于具有短官能化石墨烯的染料。综上所述，在染料中引入短官能化石墨烯是提高整体效率的有效方法，尤其是对于掺杂有较大电负性原子的石墨烯而言，因此将来可以提高DSSC的光物理性能。