The Role of Thiophene as a π-Spacer in Dye-sensitized Solar Cells: A Critical Review

Introduction: Over the past three decades, extensive research has been devoted to developing non-metallic organic dyes for dye-sensitized solar cells (DSSCs). The choice of the π-segment is critical to the device performance, as it controls not only the intrinsic electronic properties of the dye but also the energetic alignment, particularly during electron injection and dye regeneration. Method: A systematic review of published literature was used to obtain data on these dye-sensitized solar cells. Herein, we have targeted organic dyes with thiophene π-spacers and compared their efficiency with furan and benzene π-spacers. We have also discussed various dyes containing thiophene (T), bithiophene (BT) and thienothio[3,2-b] thiophene (TT) moieties. Results: Experimental and computational studies indicate that thiophene π-spacers play a critical role in DSSC performance, having a far greater impact on efficiency than other heterocyclic π-spacers. Previous studies revealed that dye with thiophene spacer group showed better efficiency (TD1 = 6.10%) than furan (TD2 = 5.5%) and benzene (TD3 = 5.1%) containing dyes. Conclusion: This review demonstrates that the use of thiophene π-spacers in DSSCs significantly improves efficiency compared to furan or phenyl rings. Oligothiophene-based π-conjugated spacers, which exhibit broad and intense absorption, show higher efficiencies than monothiophene-based spacers, underscoring their enhanced light-harvesting performance.