GQDs/Sb2S3/TiO2 as a co-sensitized in DSSs: Improve the power conversion efficiency of DSSs through increasing light harvesting by using as-synthesized nanocomposite and mirror

In present work, GQDs/Sb2S3/TiO2 composite was prepared by sonochemistry method with ultrasonic probe with 60 W/cm2 intensity and 18 kHz frequency. Based on this composite, two different cells in the configuration of FTO/TiO2/GQDs/Sb2S3/TiO2/N719/Pt and M/FTO/TiO2/GQDs/Sb2S3/TiO2/N719/Pt/GQDs/M (M:Mirror) have been fabricated to improve the efficiency of our reference devices. Optical and electrical properties of these configurations were studied by both theoretical and experimental techniques. Our experimental results indicate that the first configuration shows 43% improvement and the second configuration shows 72% improvement in PCE compare to the reference device. PDOS analysis for the charge carrier migration between GQD and TiO2. According to our theoretical results, O 2p orbitals shows the must contribution to create the valence band of TiO2 while conduction band consist of Ti 3d. DFT results show that G-S-T is more stable than S-G-T and Eb of G-S-T is more negative than S-G-T (Eb G-S-T = −3.96 and Eb S-G-T = −3.23 eV). The band gap of the G-S-T is about 0.78 eV that is less than of TiO2 and GQDs/TiO2, result in the electronic transition from the valence band to the conduction band in G-S-T is easier than that of TiO2 and GQDs/TiO2. So, excitation needs less energy. As a result, the photocatalytic performance of G-S-T is stronger than that of TiO2 and GQDs/TiO2.