Quantifying ultrafast charge carrier injection from methylammonium lead iodide into the hole-transport material H101 and mesoporous TiO using Vis-NIR transient absorption.

Organic-inorganic hybrid lead halide perovskites already reach very high power conversion efficiencies above 22% on architectures employing mesoporous TiO, but the carrier injection processes across the different interfaces are still not fully understood. Here we use ultrafast broadband transient absorption spectroscopy to determine time constants and yields for hole and electron injection. We show that hole transfer from the perovskite valence band (VB) to the hole-transport material (HTM) H101 at the perovskite/HTM interface occurs in less than 500 fs, but is limited by imperfections of the contact layer and poor infiltration of the HTM into the mesoporous structure. Electron injection from the perovskite conduction band (CB) into the CB of mesoporous TiO is only a small channel (25%). Electron transport inside mesoporous MAPI/TiO architectures therefore mainly occurs via the perovskite. We also show that electron injection from H101 into the perovskite is feasible for excitation at 400 nm resulting in light-harvesting of high-energy photons by the HTM. Accurate absolute NIR absorption coefficients for CB electrons in mesoporous TiO are provided.