Five novel metal-free organic dyes DQ1-5 containing a dipentyldithieno[3,2-f:2',3'-h]quinoxaline (DPQ) unit were synthesized and applied in dye-sensitized solar cells (DSSCs), where DPQ was employed as a π-spacer for the first time. Their photophysical, electrochemical, and theoretical calculations and photovoltaic properties were systematically investigated. All the five dyes show broad photoresponse. Especially the absorption edges of DQ3-5 extend to 800 nm on the TiO2 films. The inserted electron-rich unit 3,4-ethylenedioxythiophene or electron-withdrawing group benzothiadiazole (BTD) in DPQ-based dyes can greatly influence the optoelectronic properties of the dyes. In addition, the different electron donors also significantly affect the performance of the DSSCs. Under standard global AM 1.5 solar light conditions, the DQ5 sensitized solar cell obtained a power conversion efficiency of 7.12%. The result indicates that the rigid DPQ-based organic dye is a promising candidate for efficient DSSCs.
Keywords: dipentyldithieno[3,2-f:2′,3′-h]quinoxaline; dye-sensitized solar cells; metal-free organic dyes; optoelectronic properties; photoresponse.