Dye Aggregation, Photostructural Reorganization and Multiple Concurrent Dye···TiO₂ Binding Modes in Dye-Sensitized Solar Cell Working Electrodes Containing Benzothiadiazole-Based Dye RK-1

Journal Article · 03 December 2019 · ACS Applied Energy Materials

DOI: https://doi.org/10.1021/acsaem.9b01666 · OSTI ID:1606546

Chen, Hao ^[1]; Gong, Yun ^[2]; Vázquez-Mayagoitia, Álvaro ^[3]; Zhang, Jun ^[4]; Cole, Jacqueline M.  ^[5]

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1. Univ. of Cambridge (United Kingdom). Cavendish Lab.; Rutherford Appleton Lab., Harwell Science and Innovation Campus, Didcot, Oxfordshire (United Kingdom)
2. Univ. of Cambridge (United Kingdom). Cavendish Lab.
3. Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States
4. Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, P.R. China
5. Univ. of Cambridge (United Kingdom). Cavendish Lab. and Dept. of Chemical Engineering and Biotechnology; Argonne National Lab. (ANL), Argonne, IL (United States); Science and Technology Facilities Council (STFC), Oxford (United Kingdom). Rutherford Appleton Lab. (RAL), ISIS Neutron and Muon Facility; Rutherford Appleton Lab., Harwell Science and Innovation Campus, Didcot, Oxfordshire (United Kingdom)

Dye-sensitized solar cells (DSSCs) are widely considered to be promising contenders for the next generation of photovoltaic devices. The light-harvesting component in the DSSCs, that is, the sensitizers, are adsorbed onto the semiconductor layer to form the photoelectrode that absorbs solar energy and converts it into electrical power. The choice of dye has a profound impact on the DSSC performance. Thus, substantial research efforts have been devoted to the development and testing of a large variety of sensitizers during the past decades. We, herein, focus our attention on the metal-free benzothiadiazole-based dye, 2-cyano-3-(4-(7-(5-(4-(diphenylamino)phenyl)-4-octylthiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl) acrylic acid (RK-1), which exhibits excellent power conversion efficiency and high stability. In this work, simulations and experiments were combined to conduct a systematic study of its optical and structural properties. RK-1 shows a broad absorption band over the visible region and the formation of H aggregates in solution. Deprotonation of the cyanoacrylic acid group in RK-1 occurs upon dye adsorption onto TiO₂. This induces a hypsochromic shift of the absorption band. The emission spectrum of RK-1 shows a broad band and a large Stokes shift (6949 cm^–1), indicating the presence of several different structural reorganization processes during excitation. Time-dependent density functional theory (TD-DFT) calculations reveal that intramolecular charge transfer in RK-1 molecules should be predominantly attributed to the HOMO–LUMO transition. DFT modeling also reveals the involvement of the cyano group of RK-1 in anchoring to TiO₂, which makes the dye···TiO₂ binding structure more stable. Fourier transform infrared spectroscopy data prove that bridging bidentate (BB) and COO/CN (A2) binding modes coexist in the RK-1···TiO₂ interfacial structure.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); Science and Technology Facilities Council (STFC); Cambridge Overseas Trust
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1606546
• Journal Information: ACS Applied Energy Materials, Vol. 3, Issue 1; ISSN 2574-0962
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English