Enhanced performance of CH_3NH_3PbI_3-based perovskite solar cells by tuning the electrical and structural properties of mesoporous TiO_2 layer via Al and Mg doping

摘要

In this work, we investigate how Al and Mg doped mesoporous TiO2 layers can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs) with respect to undoped mesoporous TiO2, The PSC configuration used in this study consists of mesoscopic structure with CH3NH3PbI3 as the perovskite absorber. A PSC with optimized mol% of Al and Mg doped mesoporous TiO2 layers has been shown to achieve up to 22% higher efficiency than that of pure TiO2. While the Mg doping only enhances the open-circuit voltage (V-OC), the Al doping effectively enhances the V-OC, the short-circuit current density (J(SC)), and the fill factor (FF). The occupancy of the doped metals in the lattice is confirmed by XRD, EDX, and XPS. The Mg doping increases the band gap of TiO2 while the Al doping decreases it. The wide band gap in Mg doped TiO2 reduces the electron and hole recombination rate, thus increasing the J(SC) and V-OC. By Al doping, deep trap sites in the TiO2 are eliminated, and this effectively reduces the recombination losses and in turn, increases the J(SC). The enhanced electron-hole generation rate attributed to the decrease in the band gap of Al doped TiO2 also increases the J(SC). In addition, there is an enhancement on the electron mobility by the presence of Al metal and this gives an increase in the FF. The results have demonstrated the possibility of improving the PCE of PSCs by fine tuning the band gap of mesoporous TiO2.