Synthesis and photophysical properties of tetraphenylethylene derivatives as luminescent downshifting materials for organic photovoltaic applications

Abstract

Luminescent Down-Shifting (LDS) is an optical approach applied in several photovoltaic (PV) technologies in which high energy solar radiation is converted to a wavelength region where the response of the photovoltaic devices is better. The use of LDS layers on organic photovoltaics (OPV) could serve two purposes: to prevent cell degradation by filtering the incident ultraviolet (UV) radiation and to improve the spectral response of PV cells at short-wavelength. This work reports, the design and synthesis of a series of tetraphenylethylene (TPE) derivatives based on TPE-A or A-π-TPE-π-A molecular structure featuring various electron-acceptor (A) groups. The photophysical properties of the new LDS compounds were systematically studied in 1,4-dioxane solution and film (Zeonex) by UV–visible absorption and fluorescence spectroscopy, and electrochemical properties studied by cyclic voltammetry. Thermal stability of the new LDS compounds was evaluated by Thermogravimetric analysis (TGA). Theoretical computational studies provided evidence of existence of intramolecular charge-transfer (ICT) between frontier orbitals of donor and acceptor moieties. The good photophysical and thermal properties of the synthesized TPE derivatives, associated with high molar absorption coefficients in UV spectrum and emission maximum in the range of 476–531 nm, make them promising candidates for LDS layers in OPV application.