Efficient formamidinium–methylammonium lead halide perovskite solar cells using Mg and Er co-modified TiO₂ nanorods

We report a strategy to fabricate high quality TiO₂ nanrod array ETLs for efficient PSC devices with Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃ triple cation composition perovskite as light absorption material. Mg doped compact TiO₂ (c-TiO₂) was employed as seeds for hydrothermal growth of one-dimensional (1D) TiO₂ nanorod (NR) arrays. Assisted with these seed layers, Mg and Er doped TiO₂ rutile NR arrays were synthesized using tetrabutyltitanate (TBT) and Er(NO₃)₃ as Ti and Er precursors, respectively. It was found that uniform, straight and vertical TiO₂ NRs with a high area density were formed using Mg and Er co-modification, improving the pore-filling and crystallization of the triple cation perovskites, facilitating charge separation and suppressing recombination at the perovskite/titania NR interface of the PSC device. The shorter PL decay time with Mg/Er doping compared to the cases without Mg or Er doping is assigned to the more excellent electron extraction from the mixed cation perovskite film. The control device without modification shows an average power conversion efficiency (PCE) of 17.10%. Under the same fabrication conditions, doping of the single element Er or Mg or both Mg and Er enhances the average PCE to 17.54, 18.41 and 18.99% respectively. Our champion cell based on Mg/Er modified TiO₂ NR arrays demonstrates a PCE of 19.11%, exhibiting an enhancement of 10.33% compared with that of the PSCs based on unmodified TiO₂ NR arrays (17.32%). This work provides a simple and efficient interface engineering method to improve the efficiency of the mixed cation PSCs.