Lead halide perovskites are currently attracting a great deal of attentions due to their great promise as light absorbers in high‐efficiency hybrid organic–inorganic solid‐state solar cells. The reliable information about interface energetics of lead halide perovskite‐based interfaces is indispensable to unraveling the photon harvesting and charge separation process for this emerging photovoltaic technology. Here, we provide the direct evidence on energy level alignments at the hybrid interfaces between lead halide perovskite and organic hole‐transport materials (HTMs) using in situ ultraviolet and X‐ray photoemission techniques. The measured alignment schemes at perovskite/HTM hybrid interfaces reveal four entirely different energy level offsets with respect to the variation of HTMs, including spiro‐OMeTAD, NPB, F16CuPc, HATCN, and MoO3, and their impacts on charge separation are also elucidated. It is identified that the staggered‐gap heterojunction in contact with a HTM of higher‐lying occupied molecular orbital can facilitate the interfacial hole extraction. Our experimental findings provide the guideline of not only understanding the interfacial charge separation mechanisms but also optimizing the HTMs in perovskite‐based solar cells.

A semiconductor p-n junction typically has a doping-induced carrier depletion region, where the doping level positively correlates with the built-in potential and negatively correlates with the depletion layer width. In conventional bulk and atomically thin junctions, this correlation challenges the synergy of the internal field and its spatial extent in carrier generation/transport. Organic-inorganic hybrid perovskites, a class of crystalline ionic semiconductors, are promising alternatives because of their direct badgap, long diffusion length, and large dielectric constant. Here, strong depletion in a lateral p-n junction induced by local electronic doping at the surface of individual CH NH PbI perovskite nanosheets is reported. Unlike conventional surface doping with a weak van der Waals adsorption, covalent bonding and hydrogen bonding between a MoO dopant and the perovskite are theoretically predicted and experimentally verified. The strong hybridization-induced electronic coupling leads to an enhanced built-in electric field. The large electric permittivity arising from the ionic polarizability further contributes to the formation of an unusually broad depletion region up to 10 µm in the junction. Under visible optical excitation without electrical bias, the lateral diode demonstrates unprecedented photovoltaic conversion with an external quantum efficiency of 3.93% and a photodetection responsivity of 1.42 A W .

Organic heterostructures are a central part of a manifold of (opto)electronic devices and serve a variety of functions. Particularly, molecular monolayers on metal electrodes are of paramount importance for device performance as they allow tuning energy levels in a versatile way. However, this can be hampered by molecular exchange, i.e., by interlayer diffusion of molecules toward the metal surface. We show that the organic−metal interaction strength is the decisive factor for the arrangement in bilayers, which is the most fundamental version of organic−organic heterostructures. The subtle differences in molecular structure of 6,13-pentacenequinone (P2O) and 5,7,12,14-pentacenetetrone (P4O) lead to antithetic adsorption behavior on Ag(111): physisorption of P2O but chemisorption of P4O. This allows providing general indicators for organic−metal coupling based on shifts in photoelectron spectroscopy data and to show that the coupling strength of copper-phthalocyanine (CuPc) with Ag(111) is in between that of P2O and P4O. We find that, indeed, CuPc forms a bilayer when deposited on a monolayer P4O/Ag(111) but molecular exchange takes place with P2O, as shown by a combination of scanning tunneling microscopy and X-ray standing wave experiments.