Controlling electron injection and electron transport of dye-sensitized solar cells aided by incorporating CNTs into a Cr-doped TiO₂ photoanode

In the present work, we focused on simultaneously control electron injection and electron transport, in dye-sensitized solar cells (DSSCs), aided by introducing Cr3+ and CNTs into a TiO2 photoanode, respectively. X-ray photoelectron spectroscopy (XPS) revealed that, Cr 3+ and CNTs were successfully incorporated into the TiO2 lattice without forming secondary phases. X-ray diffraction (XRD) analysis showed that Cr introduction has perfectly balanced the amount of anatase and rutile phases in order to accomplish a more efficient cell. Field emission scanning electron microscope (FE-SEM) images showed deposited films to have a porous morphology composed of nanoparticles and TiO2 nanoparticles (TNTs) coated CNTs. Moreover, the presence of Cr3+ could improve the morphology of CNT-TiO2 electrodes. UV-vis absorption showed that Cr and CNT introduction enhanced the visible light absorption of photoanode by shifting the absorption onset to visible light region. Furthermore, the band gap energy of nanoparticles decreases with an increase in dopant concentration. The solar cell composed of 3 at.% Cr3+ and 0.025 wt% CNTs (i.e., T2/C3 cell) had the highest power conversion efficiency of 7.47%, short current density of 17.54 mA/cm2 and open circuit voltage of 698 mV. The photovoltaic improvement can be related to the achievement of a balance among the electron injection, electron transport and dye sensitization parameters.