Dye-sensitized solar cells based on organic dyes with naphtho[2,1-b:3,4- b′]dithiophene as the conjugated linker

Naphtho[2,1-b:3,4-b′]dithiophene is used for the first time as the π-spacer for metal-free organic dyes in dye-sensitized solar cells (DSSCs). Four new donor-(π-spacer)-acceptor organic dyes using triarylamine or carbazole as the electron-donating group, cyanoacrylic acid as the electron-withdrawing anchoring moiety, and naphtho[2,1-b:3,4-b′] dithiophene as the linker were synthesized. The absorption, electrochemical, and photovoltaic properties of the dyes were investigated. DSSCs based on these dyes as sensitizers had efficiencies ranging from 3.98% to 4.60%. The highest efficiency was 4.60 ± 0.16% with a J_sc of 10.8 ± 0.4 mA cm^-2, a V_oc of 657 ± 5 mV, and a fill factor of 64.0 ± 0.2% under 100 mW AM 1.5 irradiation. The incident photon-to-current efficiency (IPCE) measurement showed that these dyes had high quantum efficiency over the visible range, and the long π-spacer of the molecule resulted in broader IPCE at long wavelength and high J_sc. Photovoltage transient was used to understand the electron recombination and the trends of the photovoltaic parameters (e.g. V_oc and efficiency) of the DSSCs based on these organic dyes.