Influence of acceptor moiety in triphenylamine-based dyes on the properties of dye-sensitized solar cells

Triphenylamine-based organic dyes with different acceptor parts have been synthesized in an attempt to investigate the effect of the acceptor moiety on the properties of dye-sensitized solar cells. The light-to-electricity conversion efficiencies of 4.67% and 5.05% were obtained for the DSCs based on 2-(4-oxo-5-(4-(phenyl(4-styrylphenyl)amino)benzylidene)-2-thioxothiazolidin-3-yl)acetic acid (TPAR11) and 2-cyano-3-(4-(phenyl(4-styrylphenyl)amino)phenyl)acrylic acid (TC12), respectively. A molecular-orbital calculation shows that the delocalization of the excited state for TPAR11 is broken between the 4-oxo-2-thioxothiazolidine ring and the acetic acid, which affects the electron movement from dye molecule to the semiconductor film. The effects of chenodeoxycholic acid (CDCA) as the coadsorbent on the photovoltaic performance of the DSCs based on TPAR11 and TC12 have been also studied. It has been found that the addition of 1 mM CDCA coadsorbent improves the photocurrent for TPAR11 and the photovoltage for TC12, owing to the suppression of the quenching processes of the excited electrons between dye molecules or/and a more negative conductive band edge of TiO2 film. With the addition of 1 mM CDCA, the light-to-electricity conversion efficiencies of the DSCs based on TPAR11 and TC12 were 5.46% and 5.96%, respectively. This result indicates that both the acceptor moiety of metal-free organic dyes and the coadsorbent added in the electrode preparation have the effect on the photovoltaic performance of DSCs.