Enhancement of Perovskite Solar Cells Efficiency using N-Doped TiO₂ Nanorod Arrays as Electron Transfer Layer

In this paper, N-doped TiO₂ (N-TiO₂) nanorod arrays were synthesized with hydrothermal method, and perovskite solar cells were fabricated using them as electron transfer layer. The solar cell performance was optimized by changing the N doping contents. The power conversion efficiency of solar cells based on N-TiO₂ with the N doping content of 1% (N/Ti, atomic ratio) has been achieved 11.1%, which was 14.7% higher than that of solar cells based on un-doped TiO₂. To get an insight into the improvement, some investigations were performed. The structure was examined with X-ray powder diffraction (XRD), and morphology was examined by scanning electron microscopy (SEM). Energy dispersive spectrometer (EDS) and Tauc plot spectra indicated the incorporation of N in TiO₂ nanorods. Absorption spectra showed higher absorption of visible light for N-TiO₂ than un-doped TiO₂. The N doping reduced the energy band gap from 3.03 to 2.74 eV. The photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra displayed the faster electron transfer from perovskite layer to N-TiO₂ than to un-doped TiO₂. Electrochemical impedance spectroscopy (EIS) showed the smaller resistance of device based on N-TiO₂ than that on un-doped TiO₂.