Analysis of the charge transfer mechanism of direct Z-scheme heterojunction WSeTe/Zr₂CO₂.

As a photoelectric conversion device, dye-sensitized solar cells (DSSCs) have been attracting more and more attention, which seeks to make full use of renewable energy. Hence, four molecules, M15-G, M15-D, M15-1, and M15-2, were designed by introducing small electron-rich/deficient groups (-NH₂, -OCH₃/-CN, -F) to different positions of the π bridge of organic dye molecule M15. Herein, we comprehensively studied the structure and photoelectric performance of these molecules, explored the influence of each group introduced into different positions on the molecular performance, and estimated the photoelectric conversion efficiency (PCE) of DSSCs. The molecular planarity parameters and Bader's van der Waals volume show that the five molecules have similar configurations. The results of the excited-state charge-transfer analysis show that all molecules have the characteristics of unidirectional charge transfer excitation. In addition, compared with M15, the absorption spectrum of M15-G has a redshift, which is more conducive to the intramolecular charge transfer and thus conducive to the generation of photocurrent. And, the calculation results show that the introduction of the electron-deficient group -CN enables the M15-G to obtain theoretically a slightly greater PCE (11.65%), which also indicates that the method can be used as a reasonable strategy to improve the performance of DSSCs. GRAPHICAL ABSTRACT