We designed and synthesized two novel D–A−π–A organic dyes, POZ-4 and POZ-6, with phenoxazine (POZ) as the donor unit for application in dye-sensitized solar cells (DSSC). Our studies reveal that the introduction of the ethynyl group can optimize the planarity of the molecule and reduce the dihedral angle from 32° (POZ-4) to 2° (POZ-6), which promotes the intramolecular charge transfer (ICT) process. Hence, POZ-6 has a higher q CT value and more effective hole charge separation efficiency, ensuring that electrons are more effectively conducted from the donor (D) to the acceptor (A) unit, thereby yielding a higher molar extinction coefficient (ε) (ε POZ‑4 = 1.00 × 104 M–1 cm–1 and ε POZ‑6 = 1.70 × 104 M–1 cm–1). Furthermore, the POZ-6 device achieved a significantly higher J sc (12.95 mA cm–2) and V oc (680 mV) than that of POZ-4 (10.36 mA cm–2, 650 mV), which is attributed to the higher IPCE and τ. Correspondingly, the DSSC based on POZ-6 obtained the highest power conversion efficiency (PCE) of 6.08% (N719, 8.45%).

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Ensuring high power conversion efficiency, partially or completely replacing Pt electrodes with inexpensive materials is one of the important development directions of dye-sensitized solar cells (DSSCs). In this work, we have developed a three-component (MWCNTs, carbon black and graphite) carbon (tri-carbon) electrode material for DSSC devices combined with the advantages of high electron transfer kinetics of MWCNTs, plentiful catalytic sites in crystal edges of carbon black and superior electrical conductivity and catalytic activity of graphite. Using a tri-carbon electrode, a Pt electrode, and two N719-sensitized photoanodes, a parallel tandem dye-sensitized solar cells are assembled obtaining a high PCE of 10.26% (Voc = 0.70 V, Jsc = 19.99 mA/cm2, FF = 73.33%). It opens up a new avenue for the development of low-cost and high-performance DSSCs.