Modulation of energy levels by donor groups: an effective approach for optimizing the efficiency of zinc-porphyrin based solar cells
作者:Bo Liu、Weihong Zhu、Yueqiang Wang、Wenjun Wu、Xin Li、Baoqin Chen、Yi-Tao Long、Yongshu Xie
DOI:10.1039/c2jm16804a
日期:——
In the design of efficient sensitizers for dye-sensitized solar cells (DSSCs), it is vital to modulate the HOMO and LUMO orbitals by introducing suitable donor and acceptor groups. In this respect, triphenylamine has been extensively used as the donor group. Porphyrin has strong absorption in the UV-Vis range, which makes it a promising dye candidate. In addition, a porphyrin molecule contains eight β positions and four meso-positions, which may be conveniently utilized for introducing multiple donor and acceptor moieties. In this work, various numbers of triphenylamine and trimethoxyphenyl groups are introduced to the porphyrin meso-positions as electron donors, with the aim to systematically modulate the energy levels and investigate the effect on the efficiency of the DSSCs. The HOMO–LUMO energy gaps remain almost constant irrespective of the donor groups, thus, the variation of the donors leads to a contradictory effect on the processes of electron injection and dye regeneration. In the case of the zinc porphyrin with two triphenylamine units and one trimethoxyphenyl group as the electron donors (M3T2P), moderate and well-matched HOMO and LUMO energy levels are observed, thus affording high efficiencies for both the electron injection and the dye regeneration processes. The overall conversion efficiencies (η) of the DSSCs based on these dyes lie in the range of 2.70–5.45%, with the optimized performance achieved by M3T2P, which can be rationalized by the efficient electron injection and dye regeneration processes, and the long electron lifetime, as demonstrated by the electrochemical impedance spectroscopy measurements. These results provide further insights into the strategy for elevating the efficiencies of DSSCs, especially those based on porphyrins, simply by modulating the electron donor groups.
在设计用于染料敏化太阳能电池(DSSC)的高效敏化剂时,通过引入合适的供体和受体基团来调节 HOMO 和 LUMO 轨道至关重要。在这方面,三苯胺已被广泛用作供体基团。卟啉在紫外可见光范围内有很强的吸收能力,因此是一种很有前途的候选染料。此外,卟啉分子包含 8 个 β 位和 4 个中间位,可方便地用于引入多个供体和受体分子。在这项研究中,卟啉中位引入了不同数量的三苯胺基团和三甲氧基苯基基团作为电子供体,目的是系统地调节能级并研究其对 DSSC 效率的影响。无论供体基团如何,HOMO-LUMO 能隙几乎保持不变,因此,供体的变化会对电子注入和染料再生过程产生相互矛盾的影响。而以两个三苯胺单元和一个三甲氧基苯基为电子供体的卟啉锌(M3T2P),其 HOMO 和 LUMO 能级适中且匹配良好,因此电子注入和染料再生过程的效率都很高。基于这些染料的 DSSC 的总体转换效率(η)介于 2.70% 至 5.45% 之间,其中 M3T2P 实现了最佳性能,这可以通过高效的电子注入和染料再生过程以及较长的电子寿命得到合理解释,电化学阻抗谱测量结果也证明了这一点。这些结果使人们进一步了解了通过调节电子供体基团来提高 DSSC(尤其是基于卟啉的 DSSC)效率的策略。