Metal-free organic dyes with di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole as an auxiliary donor for efficient dye-sensitized solar cells: Effect of the molecular engineering on the photovoltaic performance

Abstract

A series of novel di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP)-based organic dyes (WL5-10) with D-D-π-A or D-D-A-π-A configurations are designed and the relationship between the properties and molecular configurations of these organic dyes are studied systematically. WL5,7–8 with D-D-π-A configuration incorporating triphenylamine or phenothiazine as donor and DBTP as auxiliary donor and WL9-10 with D-D-A-π-A configuration incorporating benzothiadiazole as an auxiliary acceptor are synthesized to study the effect of the molecular engineering on the photovoltaic performance. WL5,7–8 exhibit similar absorption spectra and high molar extinction coefficient. Especially, the dye WL5 with phenothiazine as terminal donor displays a high PCE of 6.75%, which is much higher than that of the dye WL1a with D-π-A configuration. WL9-10 show the weakest performance, which is attributed to electron trap and mismatch of energy-level due to the strongest electron withdrawing group benzothiadiazole. Finally, a high power conversion efficiency of 7.94% with chenodeoxycholic acid as the co-absorbent for the DSSC based on WL5 is achieved. The results indicate that the molecular engineering of the dyes affects the photovoltaic performance greatly, and the DBTP-based organic dye with D-D-π-A configuration by incorporating an extra terminal donor might be an effective approach to enhance the photovoltaic performance.