A thia[5]helicene based molecular semiconductor maintains π–π stacking, ensuring a large domain of molecular aggregates and a high hole mobility.

Stable, transparent organic dye-sensitized solar cells were made with over 10% efficiencies.

Exotic organic semiconductors based on helicenes are attractive because of their peculiar topology-related optoelectronic properties and good solution-processability. We herein construct pyrrole-bridged bis­(oxa[5]­helicene) and further employ it as the π-linker of a solution-processable molecular semiconductor (DOP-OMeDPA) with improved hole mobility and glass transition temperature compared with its oxa[5]­helicene counterpart. A solution-processed, doped semiconducting composite of DOP-OMeDPA presents high conductivity and slow interfacial charge recombination in perovskite solar cells, enabling the fabrication of thermostable devices with 21.3% efficiency. The DOP-OMeDPA-based thin film exhibits excellent morphology stability at 60 °C and remarkably attenuates the thermal decomposition of perovskite. Molecular dynamics modeling uncovers the microscopic origin of glass transition, that is, the torsional vibration of electron-donor for pristine materials, compared with the translational motion of molecules in doped ones.