Improved efficient perovskite solar cells based on Ta-doped TiO₂ nanorod arrays

Organometal halide perovskite solar cells (PSCs) are nowadays regarded as a rising star in photovoltaics. In particular, PSCs incorporating oriented TiO₂ nanorod (NR) arrays as the electron transport layer (ETL) have attracted significant attention owing to TiO₂ NR's superior electron transport abilities and its potential in long-term stable PSCs. In addition to improve the electron-transport ability of TiO₂ NRs, the tuning of the band alignments between the TiO₂ NR array and the perovskite layer is also crucial for achieving efficient solar cells. This work describes a facile, one-step, solvothermal method for the preparation of tantalum (Ta) doped TiO₂ NR arrays for efficient PSCs. It is shown that the trace doping with Ta tunes the electronic structure of TiO₂ NRs by a synergistic effect involving the lower 5d orbitals of the doped Ta⁵⁺ ions and the reduced oxygen vacancies. The synergistic tuning of the electronic structure improves the band alignment at the TiO₂ NR/perovskite interface and boosts the short-circuit current and the fill factor. By using the optimized doped TiO₂ NR array as the ETL, a record efficiency of 19.11% was achieved, which is the highest among one-dimensional-array based PSCs.