The solvatochromism and aggregation-induce enhanced emission of triphenylamine substituted styrene derivatives and its application in dye sensitized solar cells

Abstract

Five new triphenylamine (TPA) based D-π-A structural motifs were strategically designed and synthesized in high purity. The photophysical, electrochemical, photovoltaic properties were studied and the optimized geometry calculations of D-π-A chromophores and dyes were ascertained by DFT and TD-DFT methods. Photoluminescence properties of all the chromophores were studied in different organic solvents as well as in aggregated states. Three chromophores emit blue fluorescence in ethanol solution. However, two chromophores TPA-PHA [(E)-4′-(4-(diphenylamino)styryl)-[1,1′-biphenyl]-4-carbaldehyde], TPA-PFA [(E)-4′-(4-(diphenylamino)styryl)-2-fluoro-[1,1′-biphenyl]-4-carbaldehyde] exhibited Aggregation-induced emission enhancement (AIEE) revealing the formation of excimer in excited state. The TPA-PFA had lesser quantum yield than TPA-PHA in an aggregated state, since the m-fluorine substitution on phenyl containing chromophore makes an “inductive effect”. Substitution of aldehyde group causes enhanced formation of ICT from donor to acceptor. From FE-SEM analysis we concluded that both AIEE chromophores exhibit two different kinds of “nano-aggregates” in the solid state. The AIEE chromophores (TPA-PHA and TPA-PFA) and its derivatives i.e., Dye-1, Dye-2 were utilized in DSSC application for the first time. The dye-1 and dye-2 exhibit power conversion efficiencies (PCE) of 1.9% (Jsc = 4.68 mA/cm2, Voc = 0.70 V and FF = 0.59) and 2.1% (Jsc = 5.05 mA/cm2, Voc = 0.68 V and FF = 0.61), respectively.