Tuning the Fermi Level of TiO2 Electron Transport Layer through Europium Doping for Highly Efficient Perovskite Solar Cells

Abstract

The electron-transport layer (ETL) plays an important role in the photovoltaic performance of perovskite solar cells (PSCs), and the energy level match of functional layers can appreciably improve the power conversion efficiency (PCE) of PSCs. Herein, we choose the rare-earth europium ion Eu3+ to dope a mesoporous TiO2 ETL. X-ray diffraction, field-emission scanning electron microscopy, ultraviolet photoelectron spectroscopy, time-resolved photoluminescence, and incident-photo-to-current conversion efficiency experiments were performed to characterize the material. It is found that the Eu doping does not change the morphology, grain size, and crystallinity of TiO2. However, Eu doping upshifts the Fermi level of TiO2 ETL by scavenging oxygen atoms and introducing oxygen vacancies on the surface of the layer, which results in low series resistance and fast charge transport in the ETLs, which in turn increases the power conversion efficiency of the device from 15.85 % (undoped PSC) to 17.90 % (Eu-doped PSC). This work demonstrates an effective approach for enhancing the performance of PSCs by rare-earth doping.