Stable high-performance hybrid perovskite solar cells with ultrathin polythiophene as hole-transporting layer

Ultrathin polythiophene films prepared via electrochemical polymerization is successfully used as the hole-transporting material, substituting conventional HTM-PEDOT：PSS, in planar p-i-n CH3NH3PbI3 perovskite-based solar cells, affording a series of ITO/polythiophene/CH3NHBPbIB/C60/BCP/Ag devices. The ultrathin polythiophene film possesses good transmittance, high conductivity, a smooth surface, high wettability, compatibility with PbI2 DMF solution, and an energy level matching that of the CH3NH3PbI3 perovskite material. A promising power conversion efficiency of about 15.4%, featuring a high fill factor of 0.774, open voltage of 0.99 V, and short-circuit current density of 20.3 mA·cm^-2 is obtained. The overall performance of the devices is superior to that of cells using PEDOT：PSS. The differences of solar cells with different hole-transfer materials in charge recombination, charge transport and transfer, and device stability are further investigated and demonstrate that polythiophene is a more effective and promising hole-transporting material. This work provides a simple, prompt, controllable, and economic approach for the preparation of an effective hole-transporting material, which undoubtedly offers an alternative method in the future industrial production of perovskite solar cells.