Synthesis and characterization of perylene–bithiophene–triphenylamine triads: studies on the effect of alkyl-substitution in p-type NiO based photocathodes
作者:Martin Weidelener、Amaresh Mishra、Andrew Nattestad、Satvasheel Powar、Attila J. Mozer、Elena Mena-Osteritz、Yi-Bing Cheng、Udo Bach、Peter Bäuerle
DOI:10.1039/c2jm16847b
日期:——
We report the synthesis of new donorâÏâacceptor (DâÏâA) dyes and their application in dye-sensitized solar cells (DSCs) with nickel(II) oxide (NiO)-based photocathodes. These DâÏâA sensitizers incorporate a triphenylamine donor, a bithiophene Ï-bridge, and a perylenemonoimide (PMI) acceptor group. Two carboxylate groups attached to the triphenylamine afford strong anchoring to the NiO surface. The dyes in this series were varied firstly by the inclusion of an ethynyl linker between bithiophene and the triphenylamine moieties (1vs. 2), thereby increasing the length of the conjugated bridge. Despite very similar optoelectronic properties, the ethynyl-containing dye 2 showed a â¼25% improvement in power conversion efficiency in p-DSCs compared to 1, mostly attributed to the increased current density. Contrary to initial expectations, there was no major influence of the distance between the PMI unit of the dye and the NiO surface on the photoinduced dye anion lifetime, as measured by nanosecond transient absorption spectroscopy (TAS). Furthermore, altering the position of the alkyl chains on the bridging bithiophene in 3 and 4 resulted in a modest red shift in the dye absorption on account of increased charge delocalisation between the PMI and the Ï-bridge, owing to a reduced torsion angle between the PMI and the adjacent thiophene unit. Quantum-chemical DFT calculations were performed in order to evaluate these torsion angles and to study their influence on the electron density distribution in the relevant molecular orbitals. These changes of the molecular structure of the isomeric dyes 3 and 4 did not translate into improved photovoltaic performance, which is primarily attributed to lower charge photogeneration rates probed by transient absorption spectroscopy. While for p-type DSCs impressive overall solar-to-electric conversion efficiency of 0.04â0.10% under full sun illumination (simulated AM1.5G sunlight, 100 mW cmâ2) and a broad incident photon to current efficiency (IPCE) response (350â700 nm) is demonstrated for these new dyes, the study clearly shows the need for judicious design rules for p-type sensitizers for application in photocathodic DSCs.
我们报道了新型供体-π-受体(D-π-A)染料的合成及其在基于氧化镍(NiO)光阴极的染料敏化太阳能电池(DSC)中的应用。这些D-π-A敏化剂包含三苯胺供体、联噻吩π桥和苝酰亚胺(PMI)受体基团。两个连在三苯胺上的羧酸基团使染料与NiO表面牢固锚定。该系列染料首先通过在联噻吩和三苯胺单元之间引入乙炔连接基团(1 vs. 2)来变化,从而增加了共轭桥的长度。尽管光电性质非常相似,但含乙炔的染料2在p-DSC中与1相比显示了约25%的功率转换效率提升,这主要归因于电流密度的增加。与最初的预期相反,纳米秒瞬态吸收光谱(TAS)测量的结果显示,染料的PMI单元与NiO表面之间的距离对光诱导的染料阴离子寿命没有主要影响。此外,改变连接桥上的联噻吩上的烷基链的位置(3和4)导致染料吸收光谱的轻微红移,这是由于PMI和π桥之间的电荷离域增加,这是由于PMI和相邻噻吩单元之间的扭转角减小。进行了量子化学DFT计算,以评估这些扭转角并研究它们对相关分子轨道中电子密度分布的影响。异构体染料3和4的分子结构的这些变化并没有转化为光伏性能的改善,这主要是由于瞬态吸收光谱探测到的较低的电荷光生率。尽管对于p型DSC,在全太阳光照下(模拟AM1.5G阳光,100 mW cm⁻²)展示了令人印象深刻的总体光-电转换效率(0.04-0.10%)和广泛的入射光子-电流效率(IPCE)响应(350-700 nm),但对于这些新型染料的研究清楚地表明,在用于光阴极DSC的p型敏化剂的设计中,需要谨慎的设计规则。