Upconversion Er-doped TiO2 nanorod arrays for perovskite solar cells and the performance improvement

Upconversion erbium-doped rutile TiO2 nanorod arrays were synthesized by a facile process and applied in perovskite solar cells (PSCs). The structure was characterized by X-ray powder diffraction (XRD). Energy dispersive spectrometer (EDS) and Tauc plot indicated that Er was successfully introduced and changed TiO2 band gap from 3.00 eV to 3.07 eV. The incorporation of Er shifts the flat band potential positively and enhances the electron density. The Er-doped TiO2 nanorods have a broad absorption in the infrared light and up-convert it into visible light, which provides a possibility for PSCs to use NIR light for higher performance. A higher photo current density (J(sc)) of 22.97 mA/cm(2) and a power conversion efficiency (PCE) of 10.6% were obtained, showing 20% and 16.5% increment in J(sc) and PCE, respectively, when compared with the un-doped device. The performance improvement was ascribed to the upconversion performance, enhanced electron-injection efficiency and reduced charge recombination.