Enhanced Interfacial Binding and Electron Extraction Using Boron-Doped TiO2 for Highly Efficient Hysteresis-Free Perovskite Solar Cells

Perovskite solar cells (PSCs) have witnessed astonishing improvement in power conversion efficiency (PCE), more recently, with advances in long-term stability and scalable fabrication. However, the presence of an anomalous hysteresis behavior in the current density-voltage characteristic of these devices remains a key obstacle on the road to commercialization. Herein, sol-gel-processed mesoporous boron-doped TiO2 (B-TiO2) is demonstrated as an improved electron transport layer (ETL) for PSCs for the reduction of hysteresis. The incorporation of boron dopant in TiO2 ETL not only reduces the hysteresis behavior but also improves PCE of the perovskite device. The simultaneous improvements are mainly ascribed to the following two reasons. First, the substitution of under-coordinated titanium atom by boron species effectively passivates oxygen vacancy defects in the TiO2 ETL, leading to increased electron mobility and conductivity, thereby greatly facilitating electron transport. Second, the boron dopant upshifts the conduction band edge of TiO2, resulting in more efficient electron extraction with suppressed charge recombination. Consequently, a methylammonium lead iodide (MAPbI(3)) photovoltaic device based on B-TiO2 ETL achieves a higher efficiency of 20.51% than the 19.06% of the pure TiO2 ETL based device, and the hysteresis is reduced from 0.13% to 0.01% with the B-TiO2 based device showing negligible hysteresis behavior.