Cheema Hammad, Baumann Alexandra, Loya E Kirkbride, Brogdon Phillip, McNamara Louis E, Carpenter Casey A, Hammer Nathan I, Mathew Simon, Risko Chad, Delcamp Jared H
Chemistry Department , University of Mississippi , University , Mississippi 38677 , United States.
Department of Chemistry & Center for Applied Energy Research (CAER) , University of Kentucky , Lexington , Kentucky 40506 , United States.
ACS Appl Mater Interfaces. 2019 May 8;11(18):16474-16489. doi: 10.1021/acsami.8b21414. Epub 2019 Apr 26.
Porphyrins are attractive chromophores for application in dye-sensitized solar cells (DSCs), as judicious tuning of donor-acceptor properties can enable excellent near-infrared (NIR) absorption and exceptional device performance. Here, we report a porphyrin-based dye (SM85) conjugated to the planar strong electron donor, indolizine, designed to extend absorption further into the NIR region by inducing π-π interactions such as head-to-tail dye aggregation. The optoelectronic consequences of indolizine incorporation in SM85 include raising the ground-state oxidation potential and broadening and red-shifting ultraviolet-visible-NIR absorptions, along with increased molar absorptivity when compared to the dye SM315. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations confirm the push-pull character of SM85, which features an overlap of frontier occupied and unoccupied orbitals. Steady-state spectrophotometric analyses reveal the presence of solution aggregates via absorption and emission spectroscopies. Aggregate modes were probed by DFT and TD-DFT analyses, and plausible models are presented. SM85-based DSC devices demonstrate a 5.7% power conversion efficiency (PCE) at full sun (7.4% PCE at 10% sun) with an exceptional improvement to the incident photon-to-current conversion onset at ∼850 nm. Current dynamics measurements, time-correlated single photon counting, and computational analyses are used to better understand device performances. This study puts forward a novel intramolecular charge-transfer porphyrin system with a dramatic shift into the NIR region, as is needed for nonprecious metal-based sensitizers, and provides an example of controlled, donor-acceptor-mediated aggregation as a complementary strategy to traditional donor-acceptor modifications to single-molecule π-systems in accessing enhancements in long wavelength light harvesting in molecular-based optoelectronic devices.
卟啉是用于染料敏化太阳能电池（DSC）的极具吸引力的发色团，因为对供体 - 受体性质进行明智的调节可以实现出色的近红外（NIR）吸收和卓越的器件性能。在此，我们报告一种与平面强电子供体中氮茚共轭的卟啉基染料（SM85），其设计目的是通过诱导π - π相互作用（如头对尾染料聚集）将吸收进一步扩展到近红外区域。将中氮茚引入SM85的光电效应包括提高基态氧化电位、拓宽并红移紫外 - 可见 - 近红外吸收，与染料SM315相比，摩尔吸光率也有所增加。密度泛函理论（DFT）和含时密度泛函理论（TD - DFT）计算证实了SM85的推挽特性，其特征在于前沿占据轨道和未占据轨道的重叠。稳态分光光度分析通过吸收光谱和发射光谱揭示了溶液聚集体的存在。通过DFT和TD - DFT分析探测了聚集模式，并给出了合理的模型。基于SM85的DSC器件在全日照下表现出5.7%的功率转换效率（PCE）（在10%日照下为7.4% PCE），在约850 nm处的入射光子到电流转换起始点有显著改善。通过电流动力学测量、时间相关单光子计数和计算分析来更好地理解器件性能。本研究提出了一种新型的分子内电荷转移卟啉系统，该系统向近红外区域有显著的光谱位移，这是基于非贵金属的敏化剂所需要的，并提供了一个受控制的、供体 - 受体介导的聚集的例子，作为传统供体 - 受体对单分子π系统修饰的补充策略，以实现分子基光电器件中长波长光捕获的增强。
