Modification of photoelectrode with thiol-functionalized Calix[4]arenes as interface energy barrier for high efficiency in dye-sensitized solar cells

We successfully synthesize a series of bis-thiol-substituted calix[4]arene derivatives bearing diverse groups on the upper-rim/lower-rim (C@SH-1, C@SH-2, C@SH-3, C@SH-4, C@SH-5). For the first time, we apply these derivatives as interface modifiers for improving the photovoltaic response of a Ru-bipy dye (N-719)-sensitized TiO2 photoanode in dye-sensitized solar cells (DSSCs). We use FT-IR, H- and C-NMR, UVevis spectrophotometry, and elemental analysis techniques to characterize the structures of the calix [4]arene derivatives. We achieve an overall photon-to-electron conversion efficiency (PCE) of 12.97% with the DSSCs based on 25,27-bis(5-thiol-1-oxypentane)-26,28-dihydroxycalix[4]arene (C@SH-3)- modified TiO2 photoanode (Jsc ¼ 9.49 mA cm2 , Voc ¼ 672 mV, FF ¼ 61.1%) compared with a system of bare TiO2 (PCE: 6.82%) under AM 1.5G illumination of 300 W/m2 . In addition, we also study the influence of the chain length (C@SH-2; with 3 carbons and C@SH-3; with 5 carbons) and subsidiary ligand groups such as alkyl (C@SH-1), nitro (C@SH-4), and amine (C@SH-5) on the surface morphology, spectral response, and photovoltaic performance. Our results reveal that the C@SH-3 calixarene is the best derivative for modifiying the TiO2 photoanode. Thiol-functionalized Calix[4]arene molecules play a role in assisting charge separation and preventing back recombination, which accounts for the observed enhancement in photovoltaic performance.