(a) Photo current–voltage curves, (b) IPCE spectra, (c) recombination resistance under light, and (d) high frequency resistance under light for the perovskite solar cells based on ZnO nanorods grown on three different seed layers. Reproduced with permission from D.-Y. Son, K.-H. Bae, H. S. Kim and N.-G. Park, J. Phys. Chem. C, 2015, 119, 10321–10328. Copyright (2015) American Chemical Society.34