Hierarchical core–shell heterostructure of H2O-oxidized ZnO nanorod@Mg-doped ZnO nanoparticle for solar cell applications
Herein, a core–shell heterostructure of H2O-oxidized ZnO nanorod (NR)@Mg-doped ZnO (MZO) nanoparticles (NP) with superior charge transfer capabilities is presented for the first time. ZnO NRs were strategically designed using a low-temperature and sustainable H2O oxidation technique and followed by low-temperature annealing of a spin-coated MZO precursor to form a core–shell heterostructure. Surface morphological and nanobeam electron diffraction (NBD) analysis validated the high-quality crystalline nature of the core–shell heterostructure. The verification of Mg dopant inclusion in the ZnO lattice and uniform distribution were established from X-ray (XRD, XPS, EDX), Raman and electron energy-loss (EELS) spectroscopy analyses. The ZnO NR@MZO NP core–shell film preserved the excellent transparency of the original ZnO NRs and displayed the highest conductivity due to the increased carrier concentration in the MZO shell. Steady-state photoluminescence (PL) intensity of the perovskite film on top of the ZnO NR@MZO NP core–shell film showed the strongest quenching among the samples indicating the fastest electron transfer. This ZnO NR@MZO NP core–shell heterostructure could provide a more efficient transmission channel by supplying a larger electronic contact with the light absorber layer and a direct path for electron transport to the cathode. Ultimately, our results highlight the great potential of the ZnO NR@MZO NP core–shell structure as an electrode not only for photovoltaics but also in other future flexible optoelectronic devices.