Novel D–A−π–A Organic Dyes with Phenoxazine as a Donor Unit for Dye-Sensitized Solar Cells: The Effect of an Ethynyl Group on Performance
Shu Mei, Wu Shao, Shucheng Huang, Xiangfei Kong, Zhenguang Hu, Miao Yang, Wenjun Wu, Haijun Tan
Abstract
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 qCT 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) (εPOZ-4 = 1.00 × 104 M–1 cm–1 and εPOZ-6 = 1.70 × 104 M–1 cm–1). Furthermore, the POZ-6 device achieved a significantly higher Jsc (12.95 mA cm–2) and Voc (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%).