LiTFSI-Free Hole Transport Materials for Robust Perovskite Solar Cells and Modules with High Efficiencies

Lithium bis(trifluoromethane) sulfonamide (LiTFSI) and oxygen-doped organic semiconductors have been frequently used to achieve record power conversion efficiencies of perovskite solar cells (PSCs). However, this conventional doping process is time-consuming and leads to poor device stability due to the incorporation of Li ions. Herein, aiming to accelerate the doping process and remove the Li ions, we report an alternative p-doping process by mixing a new small-molecule organic semiconductor, N2,N2,N7,N7-tetrakis (4-methoxyphenyl)-9-(4-(octyloxy) phenyl)-9H carbazole-2,7-diamine (labeled OH44) and its preoxidized form OH44+(TFSI–). With this method, a champion efficiency of 21.8% has been achieved for small-area PSCs, which is superior to the state-of-the-art EH44 and comparable with LiTFSI and oxygen-doped spiro-OMeTAD. Moreover, the stability of OH44-based PSCs is improved compared with those of EH44, maintaining more than 85% of its initial efficiency after aging in an ambient condition without encapsulation for 1000 h. In addition, we achieved efficiencies of 14.7 and 12.6% for the solar modules measured with a metal mask of 12.0 and 48.0 cm2, respectively, which demonstrated the scalability of this method.