Molecular Gelation-Induced Functional Phase Separation in Polymer Film for Energy Transfer Spectral Conversion

A new strategy for creating the energy transfer spectral conversion thin film by using fluorophore-functionalized molecular gelation is proposed. This is based on the facts that nanofibrillar phase separation of the self-assembling pyrene derivative as a fluorophore is formed in a bulk polymer-containing organic gel, and consequently that the phase-separated nano domain in a polymer thin film is enough small to keep the transparency but also extremely high Storks shift is gained by efficient excimer formation through highly ordered stacking among the pyrene moieties. When the phase separation-mediated functional polymer is applied as spectral conversion films (SCFs) for copper-indium-gallium-selenide (CIGS) solar cell, the SCF-covered solar cell exhibits significant improvement of power conversion efficiency by increase of photocurrent. In this paper, the FRET efficiency and emission wavelength are also demonstrated to be thermotropically switchable since order-to-disordered transitions are essential characteristics of as non-covalent low molecular assembling.