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

•Two simple co-sensitizers were synthesized for N719-based DSSCs.•The co-sensitizers could avoid dye aggregation and reduce charge recombination.•Both Jsc and Voc of the co-sensitized DSSCs were enhanced relative to single N719.•Co-sensitization of a DSSC with N719 and LD04 exhibited the highest PCE of 8.955%.

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 (Jsc) and open circuit voltage (Voc) simultaneously, which owing to the co-sensitizers could effectively overcome the competitive light absorption by I3− 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% (Jsc = 17.628 mA cm−2, Voc = 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).

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