Inverted pyramid Er3+ and Yb3+ Co-doped TiO2 nanorod arrays based perovskite solar cell: Infrared response and improved current density

In this study, a Yb3+, Er3+ co-doped TiO2 inverted pyramid nanorod (NR) array and a compact TiO2 film are simultaneously fabricated as the mesoporous support layer and electron-blocking layer, respectively, by a one-pot hydrothermal method. The scanning electron microscopy results show that the incorporation of Er3+ and Yb3+ causes changes not only in the growth rate of the NRs, but also in the TiO2 NR morphology. The Er3+, Yb3+ co-doped TiO2 NRs exhibit an inverted pyramidal morphology, which is beneficial for perovskite permeation and light utilization. Notably, the Er3+, Yb3+ co-doping causes changes in the band gap of TiO2 and leads to 25% increase in the current density. The electrochemical impedance spectroscopy results show that the device based on the doped TiO2 NRs has a higher recombination resistance and a lower transfer resistance than those of the undoped device, and thereby, the doped device exhibits a lower electron recombination rate. In addition, the upconversion Er and Yb co-doped device exhibits 25% higher current density and 17% higher photon-to-electron conversion efficiency, as revealed by the J-V test results. Moreover, the optimized efficiency of the TiO2 NR array-based perovskite solar cell is determined to be 10.02%. Furthermore, the Er and Yb co-doped device exhibits a near-infrared response, an efficiency of 0.1% is achieved under infrared light (800–1100 nm) irradiation. This upconversion material can widen the photovoltaic responses of solar cells into the near-infrared region and improve the utilization of sunlight.