Influence of the donor size in panchromatic D–π-A–π-A dyes bearing 5-phenyl-5H-dibenzo-[b,f]azepine units for dye-sensitized solar cells

Two D–π-A–π-A organic dyes (YC-1 and YC-2) with 5-phenyl-5H-dibenzo[b,f]azepine derivatives as donor, thiophene as π bridge, and isoindigo and cyanoacrylic acid as acceptors were prepared. YC-1 and YC-2 show a panchromatic absorption between 300 nm and 800 nm both in solution and neat film. The photovoltaic performances of both dyes were evaluated in dye-sensitized solar cells based on iodide/triiodide electrolyte without any co-sensitizer. The YC-1 based device displays better device performance with open-circuit photocurrent density of 12.12 mA cm−2, open-circuit voltage of 0.53 V, and fill factor of 68.9%, corresponding to overall conversion efficiency (η) of 4.38%. The inferior performance of device based on YC-2 (η = 1.46%) is ascribed to short electron lifetime as evidenced from electrochemical impedance spectroscopy measurement. This research provided a potential promising donor unit for organic dyes and revealed the influence of donor size in organic dyes for photovoltaic performances. •Tow D-π-A-π-A dyes bearing 5-phenyl-5H-dibenzo-[b,f]azepine units were synthesized.•The effect of donor size on the property of sensitizer was systematically studied.•The dyes show panchromatic absorption between 300 and 800 nm in solution and neat film.•PCE of 4.38% was achieved for DSSCs based on I3−/I− electrolyte without co-sensitizer.