Recent Progress in the Development of Eco-Friendly Processed Organic Solar Cells: Experiments and Theory
Résumé
Synergic effects concerning electronic structure and morphology in the PTB7-Th polymer and the non-fullerene acceptor ITIC molecule has resulted in state-of-art systems for organic solar cells (OSCs), achieving over 12% PCE values [1]. Furthermore, the substitution of harmful halogenated solvents to environmentally friendly solvents that do not compromise PCE values has become a subject of great interest in the literature [2]. In this work, we employed sulfur K-edge Angle-Resolved Near-Edge X-ray Absorption Fine Structure (NEXAFS), Resonant Auger (RAS), and the Core-Hole Clock spectroscopies in an attempt to gain information on the effect of different processing methods on the elec- tronic and morphological properties of these systems. These spectroscopic measurements (NEXAFS, RAES and XPS) were carried out at the SXS beamline of the Brazilian Syn- chrotron Light Laboratory (LNLS). In order to compare the use of an conventional acceptor molecule, we have performed Steady State and Time-Resolved Photoluminescence (TRPL) experiments for neat PTB7- Th and blends with ITIC and PCBM. TRPL measurements were carried at the Swansea’s Material Research Centre. To a better comprehension of the sulfur excited states involved in the electronic tran- sitions probed by the synchrotron-based-spectroscopic methods, theoretical calculations were performed utilizing Restricted-Excitation-Window Time-Dependent Density Functional Theory (REW-TD-DFT). In order to probe the extent of relativistic effects present in these transitions, we employed different Hamiltonians (ZORA, DKH, X2C) in our calculations. We also explored different chemical descriptors (the Donor-Acceptor and Aromatic- Quinoid approaches) to obtain information at valence level in both ground and low-lying excited states. All calculations were performed in NWChem 7.0, Gaussian16 and Amsterdam Density Functional (ADF).
[1] Jianhui Hou et al. “Organic solar cells based on non-fullerene acceptors”. In: Nature materials 17.2 (2018), pp. 119–128.
[2] Jingbo Zhao et al. “Efficient organic solar cells processed from hydrocarbon solvents”. In: Nature Energy 1.2 (2016), pp. 1–7.
[1] Jianhui Hou et al. “Organic solar cells based on non-fullerene acceptors”. In: Nature materials 17.2 (2018), pp. 119–128.
[2] Jingbo Zhao et al. “Efficient organic solar cells processed from hydrocarbon solvents”. In: Nature Energy 1.2 (2016), pp. 1–7.