Direct Observation of Ultrafast Hole Injection from Lead Halide Perovskite by Differential Transient Transmission Spectroscopy.

Efficient charge separation at the interfaces of the perovskite with the carrier transport layers is crucial for perovskite solar cells to achieve high power conversion efficiency. We present a systematic experimental study on the hole injection dynamics from MAPbI perovskite to three typical hole transport materials (HTMs). We extract the carrier dynamics directly related to the hole injection by employing a pump light with short absorption depth and comparing the transient transmission signals excited on the two sides of the sample. The differential transmission signals reveal the hole injections to PTAA and PEDOT:PSS to be complete within 1 and 2 ps, respectively, and that to NiO to exhibit an additional slow process on a 40 ps time scale. The obtained injection dynamics are discussed in comparison with the device performance of the solar cells containing the same MAPbI/HTM interfaces.