Modified pyrene based organic sensitizers with thiophene-2-acetonitrile as π-spacer for dye sensitized solar cell applications

• Synthesized metal free organic sensitizers for fabrication of dye sensitized solar cells.
• The solid state absorption spectrum of PTC and PTR dye adsorb on TiO2 film shows J- and H- type aggregation.
• The spatial separation is high for PTC dye illustrates the effective and fast electron injection from excited dye to TiO2 film.
• Noticed decreased electron injection yield and open circuit voltage due to aggregation of the PTR dye.
• The co-adsorbent deoxycholic acid was added to suppress the dye aggregation.

Designed, synthesized and characterized two new metal free organic sensitizers for dye-sensitized solar cells (DSSCs) applications comprising pyrene-1-carbaldehyde as donor, thiophene-2-acetonitrile as π-spacer and cyano acetic acid or rhodanine-3-acetic acid as electron acceptor moieties. From photophysical properties, J and H- type dye aggregations observed for the cyano acetic acid and rhodanine-3-acetic acid anchor group based dyes respectively. The electrochemical experiments and time-correlated single-photon counting (TCSPC) measurements indicate the ability of electron injection into the TiO2 conduction band from the excited sensitizer. Theoretical calculations were performed to rationalize the experimental data and both experimental and theoretical studies indicate that rhodanine-3-acetic acid anchor groups at the acceptor moiety inhibit the electron injection process due to H-type dye aggregation which in turn decreases the open circuit voltage (Voc). Furthermore, the electrochemical impedance spectroscopy (EIS) experiments suggest that the effective electron injection, low charge transfer resistance (Rct), longer lifetime of dye on TiO2 film assists the increase of Voc, achieved by the addition of co-adsorbent deoxycholic acid which in turn enhances the power conversion efficiency (η%).

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