TiO2-based electron transport layers (ETLs) show tremendous advantages in constructing efficient perovskite solar cells (PSCs), but the power conversion efficiency (PCE) needs further improvements. Thus, in this study, graphitic carbon nitride (g-C3N4), a typical two-dimensional material, was synthesized in-situ and introduced into TiO2-based ETLs as an additive via a facile glass-assisted annealing route. The results demonstrated that the addition of g-C3N4 positively influenced the crystalline quality of the perovskite layers, as well as the conductivity and photovoltaic properties of the devices. Furthermore, favorable energy level alignment facilitated rapid migration of electrons and suppressed charge recombination at the interfaces. Consequently, the champion device fabricated using the g-C3N4-modified ETL achieved a maximum PCE of 20.46% owing to the remarkable improvement in the V-OC, J(SC), and fill factor. The PCE is approximately 20% higher than that obtained for the pristine device, i.e., 17.18%. (C) 2021 Elsevier Inc. All rights reserved.