Effect of Transition Metal Doping in the ZnO Nanorod on the Efficiency of the Electron Transport Layer in Semitransparent CsPbBr3 Perovskite Solar Cells

We have grown vertically ZnO nanorods (NRs) doped with Cu and Ni to modulate their electronic properties. The wurtzite structure of the ZnO NRs was confirmed from the top-view field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images as well as X-ray diffraction (XRD) spectra, and the phase purity was confirmed by Raman spectroscopy. The NRs exhibit high texture orientation in the (002) and (100) directions of the Ni- and Cu-doped ZnO NRs, respectively. This structural modification significantly modulates their electronic properties. Scanning tunneling spectroscopy (STS) and corresponding density of states (DOS) measurements were employed to determine the electronic band gap and band-edge shift of the doped ZnO NRs. Ambient-processed semitransparent CsPbBr3 perovskite solar cells (PSCs) were fabricated with the device structure (FTO/ZnO seed layer/ZnO NRs:CsPbBr3/Spiro-MeOTAD/ITO) using these NRs as the electron transport layer (ETL). The Ni-doped ZnO NR samples were found to be very good in electrical conductivity with a low electronic band gap, which yielded a device power conversion efficiency (PCE) of 4.94% under ambient conditions. Thus, Ni-doped ZnO NRs could be used as an efficient low-cost and ambient-processed one-dimensional ETL in the fabrication of optoelectronic devices.