Amino-Functionalized Niobium-Carbide MXene Serving as Electron Transport Layer and Perovskite Additive for the Preparation of High-Performance and Stable Methylammonium-Free Perovskite Solar Cells

Perovskite solar cells have shown great potential in commercial applications due to their high performance and easy fabrication. However, the electron transport layer (ETL) materials with good optoelectrical properties and energy levels matching that of the perovskite layer still need to be explored to meet the need of commercialization. In this work, 2D Nb2CTx MXene nanosheets are prepared and their work function (WF) is reduced from 4.65 to 4.32 eV to match the conduction band minimum of perovskite layer by replacing the surface -F groups with -NH2 groups through hydrazine (N2H4) treatment. Besides, the N2H4 treated (T-Nb2CTx) MXene nanosheets with abundant -NH2 groups are incorporated into the perovskite precursor to retard the crystallization rate by forming hydrogen bond with iodine ions, which promotes the formation of high-quality and oriented growth perovskite films. Consequently, the PVSCs with T-Nb2CTx MXene ETLs and T-Nb2CTx MXene nanosheets additive exhibit the highest power conversion efficiency (PCE) of 21.79% and the corresponding flexible and large-area devices achieve the highest PCE of 19.15% and 18.31%. Meanwhile, the unencapsulated devices maintain 93% of the original PCEs after 1500 h of storage. This work demonstrates the considerable application prospects of 2D Nb2CTx MXene in photoelectric devices.

Automated summary

In this work, 2D Nb2CTx MXene nanosheets were prepared and used as electron transport layer (ETL) materials in perovskite solar cells. By altering the surface groups of the MXene nanosheets, the work function was matched with the conduction band minimum of the perovskite layer, resulting in improved performance of the solar cells. Additionally, the incorporation of treated MXene nanosheets into the perovskite precursor helped in the formation of high-quality and oriented growth perovskite films, leading to higher power conversion efficiency (PCE). The flexible and large-area devices with MXene ETLs and additives achieved the highest PCE. Furthermore, the unencapsulated devices demonstrated good stability after long-term storage.