A co-sensitized approach to efficiently fill the absorption valley, avoid dye aggregation and reduce the charge recombination

Compared with the development of novel organic dyes, co-sensitization is a much more convenient way to achieve highly efficient dye-sensitized solar cells (DSSCs). Here, two simple donor-(π conjugated spacer)-acceptor dyes, in which hexyloxy-substituted phenyl as an electron donor, cyanoacrylic acid as the electron acceptor and different spacers thiophene ( LD03 ) or furan ( LD04 ) as the π-linkers, were designed and synthesized as co-sensitizers for N719 -based DSSCs . The photophysical, electrochemical, photovoltaic performances and electrochemical impedance spectroscopy of these DSSCs were investigated in detail. When compared to the DSSCs fabricated from individual N719 , the co-sensitized DSSCs ( N719   +   LD03 and N719   +   LD04 ) showed significantly enhanced power conversion efficiencies (PCEs), short-circuit photocurrent density ( J sc ) and open circuit voltage ( V oc ) simultaneously, which owing to the co-sensitizers could effectively overcome the competitive light absorption by I 3 − in the electrolyte, avoid dye aggregation and reduce the charge recombination. Consequently, the co-sensitized DSSC ( N719   +   LD04 ) gave the highest PCE of 8.955% ( J sc   =   17.628   mA   cm −2 ,   V oc   =   0.758   V and fill factor   =   0.670), exhibiting an improvement of 13.412% compared to the device sensitized with N719 alone (PCE   =   7.896%) under illumination (AM 1.5G, 100   mW   cm −2 ).