High-efficient hole-transport-material-free carbon-based all-inorganic perovskite solar cells using Cs-doped TiO2 nanorods array as the electron transport layer

Vertical-oriented Cs-doped rutile TiO2 nanorod (Cs-TiO2 NR) arrays were prepared without a seed layer through the hydrothermal method. One-dimension TiO2 nanorod (TiO2 NR) arrays not only provide a direct and fast channel for charge transfer but also increase the perovskite loading amount. Further research shows that the conduction band minimum of Cs-TiO2 NRs increases from − 3.94 eV to − 3.86 eV when compared with the pristine TiO2 NRs, which favors the positive band alignment at the ETL/perovskite interface and reduces the carrier recombination and energy loss. Furthermore, we simultaneously replaced the expensive and unstable organic hole transport layer and noble metal electrode with a carbon electrode for the purpose of reducing the cost of the PSCs. The study proves that Cs-TiO2 NRs not only improve the energy level arrangement at the ETL/perovskite interface but also reduce the density of defect states at the interface and increase carrier lifetime. The hole-transport-material-free carbon-based all-inorganic FTO/Cs-TiO2 NRs/CsPbI2.25Br0.75/C solar devices exhibited a high-power conversion efficiency (PCE) of 12.72%, showing a 16% increase in PCE when compared with the control device. This work opens the door to the preparation of high-efficiency hole-transport-material-free carbon-based all-inorganic PSCs via the energy level calibration engineering.