Determination of complex optical constants of PBDB-T-2F/ITIC-4F organic solar cells
Anil Kumar Bharwal a, Yatzil Avalos b, Carmen Ruiz-herrero a, Olivier Margeat b, Christine Videlot-Ackermann b, Jorg Ackermann b, Ludovic Escoubas a, David Duché a, Jean-Jacques J.J. Simon a
a Aix-Marseille Univ., Univ. Toulon, UMR CNRS 7334, Institut Matériaux Microélectronique Nanoscience de Provence (IM2NP), Marseille, France
b Aix-Marseille University, Centre Interdisciplinaire de Nanosciences de Marseille CINaM, UMR CNRS 7325, Marseille, France, CINaM Campus de Luminy, Marseille, 13288, France
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Anil Kumar Bharwal, presentation 133
Publication date: 20th April 2022

Solution-processed bulk-heterojunction organic solar cells (OSCs) have arisen as a promising alternative to inorganic solar cells due to their transparency, flexibility, and improved power conversion efficiency (PCE) [1–3]. At present, the PCE of OSCs has surpassed 18%, beginning to compete with the different PV technologies existing at an industrial scale [4,5]. To achieve a firm cost reduction for an existing market, OSCs based on non-fullerene acceptors (NFA) based molecules are of great interest [6,7]. In an OSC device, the photoactive layer comprising of electron donors and acceptors is the core component for photoelectric conversion. However, understanding the complex optical constants of the active layer of OSC is very important for the optimization of the OSCs. For this purpose, spectroscopic ellipsometry measurements are performed to determine the optical properties of the ITIC-4F NFA and PBDB-T-2F donor-based active layer. In this work, we report the optical characterizations and modeling to investigate the intermolecular interactions and electronic transition of ITIC-4F and PBDB-T-2F, likely playing a key role in affecting both PCE and stability. The energies of the optical transitions and the bandgap of the PBDB-T-2F and ITIC-4F as well as of their blends are determined using a Gaussian model and compared to the experimental results obtained from UV-photospectrometry (figure 1a). Small changes in optoelectronic transitions in the blends as compared to pure materials are attributed to the material interactions (figure 1b) which resulted in improved solar cell stability. Additionally, we performed a comparison between fresh and aged samples based on both pure and blend materials by optical measurements. The optical results showed that the blend materials in both fresh and aged conditions were more stable than the pure ones, further confirming that the stability of blends-based solar cells is improved by material interactions.

This work is supported by the NFA-15 project (Project no- ANR-17-CE05-0020).

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