Facile synthesis of triphenylamine-based hole-transporting materials for planar perovskite solar cells

Three new small-molecule triphenylamine-based hole-transporting materials are easily synthesized by using commercially available and inexpensive starting reagents as a precursor. They are applied as new small-molecule hole-transporting materials for planar cesium-containing triple-cation mixed-halide perovskite solar cells using tin oxide, yielding efficiency values over 18%. The new compounds adopt a benzene-pi-triphenylamine structure and have reasonable energy levels. The positions of the substituents on the central benzene ring are different. Perovskite solar cells devices on the basis of these new compounds show good reproducibility and significantly suppressed hysteresis. According to the steady-state and time-resolved photoluminescence, space-charge-limited current, and electrical impedance spectroscopy analyses, our devices using the new compounds show higher power conversion efficiency than the state-of-the-art 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene under the same conditions because of faster charge transport and lower recombination losses. Therefore, these new triphenylamine-based molecules are promising candidates for cost-effective hole transport materials in use of fabrication of highly efficient perovskite solar cells.