Y-shaped organic dyes with D2-π -A configuration as efficient co-sensitizers for ruthenium-based dye sensitized solar cells

Three new Y-shaped organic dyes, coded CD1-3, have been synthesized for dye-sensitized solar cells (DSSCs). They have a D2-pi -A configuration and been molecularly engineered to modulate the spectral properties and energy levels. For comparison, a D-pi -A type sensitizer with one donor group (CD4) is synthesized as well. We have performed a combined experimental and theoretical investigation of their optical, electrochemical, photovoltaic, geometrical and electronic characteristics. These new Y-shaped dyes display intensive UV-vis absorption with high molar extinction coefficients. So their roles as co-sensitizers for ruthenium-based DSSCs are further evaluated. As a consequence, the co-sensitized devices exhibit improved power conversion efficiencies (PCEs) in the range of 7.24-7.96% due to the enhanced short-circuit photocurrents (Jsc) and open-circuit voltages (Voc), which are higher than the DSSCs sensitized with N719 (PCE = 6.75%) or Z907 (PCE = 6.55%) alone. In addition, the mechanisms of these improvements have been elucidated by incident photon to current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) studies. The Jsc is improved because CD1-3 can compensate for the photocurrent loss by I-/I3; while the Voc is enhanced because the electron recombination process is retarded by these Y-shaped dyes upon co-sensitization. Superscript/Subscript Available

Automated summary

Three new Y-shaped organic dyes were synthesized for dye-sensitized solar cells, leading to improved power conversion efficiencies due to enhanced short-circuit photocurrents and open-circuit voltages. Experimental and theoretical investigations showed that the new dyes can compensate for photocurrent loss and retard electron recombination, resulting in better performance of the DSSCs.