Doping amino-functionalized ionic liquid in perovskite crystal for enhancing performances of hole-conductor free solar cells with carbon electrode

Amino group functionalized hydrophobic ionic liquid, 1-ethylamine hydrobromide-3-methylimidazolium hexafluorophosphate (ILPF6) ionic liquid, was employed as the functional monomer to fabricate a carbon-based hole-conductor-free perovskite solar cells with high performances. The photoactive perovskite layer was facilely acquired by one-step spin-coating the precursor solution on a TiO2/FTO electrode surface, and subsequently annealed at an initial annealing at 60 degrees C for 3 min followed by annealing at 100 degrees C for 10 min to crystallize. The perovskite precursor solution was prepared by mixing ILPF6 ionic liquid and methylammonium iodide with an equal molar ratio of PbI2. In the optimized conditions, the power conversion efficiency (PCE) was enhanced from 10.08% to 13.01% by doping ILPF6 into the perovskite crystal film. This study demonstrates the multifaceted functions of ILPF6 ionic liquid in improving the efficiency and stability of PSCs. First, ILPF6 can react with PbI2 to form perovskite and can also play a role of the controlling and crosslinking reagent to obtain large grain size and minimize defects. Secondly, ILPF6 can improve the loading amount of perovskite crystals on the TiO2 film. Third, ILPF6 can promote the transport rate of the photogenerated carriers in the perovskite crystal layer. Lastly, ILPF6 ionic liquid with its high hydrophobicity creates a moisture barrier to improve the stability of PSCs effectively. The PSCs were stored under dark in a low relative humidity atmosphere (RH of 20%) at 25 degrees C without sealing. After 840 h, the PSC can maintain 94% of its initial PCE under the identical intensity illumination. This study demonstrates an excellent strategy to break through the bottleneck of the traditional PSCs and the enhanced effect of ionic liquid for carbon-based PSCs.