Rational tailoring of electron-donating arms toward promising thia[5]helicene-based hole-transporters for stable and efficient perovskite solar cells

Due to the unique π-curved molecular conformation, the helicenes exhibit a variety of favorable properties, such as multi-dimensional hole transport and good phase stability. In this work, five helicene type hole-transport materials (HTMs) are designed by using thia[5]helicene as π-linker, conjoined with different donors include methoxybiphenyl, phenyl-naphthylamine, fluorene, N-ethylcarbazole and dibenzothiophene to probe the effects of electron-donating arms. Compared to experimental reported T5H-OMeDPA, all tailored HTMs exhibit more stable HOMO levels. The matched energy levels mean that the advantageous charge transfer at the interface can be expected. Importantly, by employing the π-extended dibenzothiophene to decorate the electron-donating unis, the SM55 shows the highest hole mobility compared to the other HTMs. The influence of steric hindrance is overcome by the enhanced sulfur-sulfur interactions. The favorable solubility and hydrophobicity are also exhibited for new designed HTMs. Meanwhile, the interfacial simulations show that the adsorbed FAPbI₃/SM55 system exhibits more stable adsorption conformation and the greater charge transfer and work function at the interface compared to T5H-OMeDPA, which is potentially helpful for photogenerated electron-hole separation. This work not only offer the promising helicene-typed HTMs, but also present the beneficial insights for experimental synthesis.