Molecular Engineering of Fluorene-Based Hole-Transporting Materials for Efficient Perovskite Solar Cells

New Spiro-OMeTAD analogues and the simpler half structures with the terminated methoxyphenyl and/or carbazolyl chromophores are successfully synthesized under Hartwig-Buchwald amination conditions using commercially available starting materials. New fluorene-based hole-transporting materials combined with suitable ionization energies properly align with the valence band of the perovskite absorber. Additionally, these compounds are amorphous, which is an advantage for the formation of homogenous films, as well as eliminate the possibility for films to crystallize during operation of the devices. The most efficient perovskite solar cells devices contain carbazolyl-terminated SpiroOMeTAD analogue V1267 and reach a power conversion efficiency of 18.3%, along with a short-circuit current density, open-circuit voltage, and fill factor of 23.41mA cm(-2), 1.06 V, and 74.0%, respectively. Moreover, half structures with methoxyphenyl/carbazolyl fragments show excellent long-term stability and outperform Spiro-OMeTAD and, therefore, hold a great prospect for practical wide-scale applications in optoelectronic devices.

Automated summary

New Spiro-OMeTAD analogues and half structures with methoxyphenyl and/or carbazolyl chromophores as terminations are successfully synthesized under Hartwig-Buchwald amination conditions. These compounds properly align with the valence band of perovskite absorber, and their amorphous nature is advantageous for the formation of homogenous films. The most efficient solar cell device reaches a power conversion efficiency of 18.3% and exhibits excellent long-term stability.