Efficiency improvement of dye-sensitized solar cells by in situ fluorescence resonance energy transfer

A 1,8-naphthalimide derivative (H-NIM) containing an alkyl carboxylic chain has been rationally designed and synthesized for efficient utilization of fluorescence resonance energy transfer (FRET) in dye-sensitized solar cells (DSSCs). The H-NIM fluorophore, which can absorb ultraviolet light and emit green light under illumination, is doped into a TiO2 mesoporous film with N719 molecules by a co-adsorption method. The H-NIM fluorophore adsorbs on the TiO2 by the same method as N719, via its carboxylic groups, ensuring more efficient energy transfer from H-NIM (FRET donor) to N719 (FRET acceptor) via in situ FRET and thereby promoting light harvesting of N719 molecules in the spectral range of ultraviolet light. The co-adsorption of H-NIM and N719 also reduces charge recombination by shielding the contact area between TiO2 and the electrolyte. Our results show that the optimal doping ratio of the H-NIM fluorophore is 17%, at which the power conversion efficiency (PCE) of the DSSC is improved by 10.8% and 21% under one sun (AM1.5G) and 600 lux illumination by T5 fluorescent lamps, respectively, compared with a DSSC in which only N719 molecules were adsorbed.