High power conversion efficiency (PCE) perovskite solar cells (PSCs) rely on optimal alignment of the energy bands between the perovskite absorber and the adjacent charge extraction layers. However, since most of the materials and devices of high performance are prepared by solution‐based techniques, a deposition of films with thicknesses of a few nanometers and therefore a detailed analysis of surface and interface properties remains difficult. To identify the respective photoactive interfaces, photoelectron spectroscopy measurements are performed on device stacks of methylammonium‐lead‐iodide (MAPI)‐based PSCs in classical and inverted architectures in the dark and under illumination at open‐circuit conditions. The analysis shows that vacuum‐deposited MAPI perovskite absorber layers are n‐type, independent of the architecture and of the charge transport layer that it is deposited on (n‐type SnO2 or p‐type NiOx). It is found that the majority of the photovoltage is formed at the n‐MAPI/p‐HEL (hole extraction layer) junction for both architectures, highlighting the importance of this interface for further improvement of the photovoltage and therefore also the PCE. Finally, an experimentally derived band diagram of the completed devices for the dark and the illuminated case is presented.

We have studied the electronic structure of CH3NH3PbI3 (MAPI) and CH3NH3SnI3 (MASI) perovskite films by performing X-ray photoelectron spectroscopy (XPS) measurements on in situ grown perovskite films.

In this work, the characterization of methylammonium lead iodide (MAPI) layers fabricated with a modified two-step deposition technique under high vacuum is presented. Thereby, PbI 2 , deposited in an open sublimation process, is exposed to methylammonium iodide (MAI) vapor in a closed crucible. The fabricated layers are examined with scanning electron microscopy (SEM), X-ray diffraction (XRD), UV/VIS absorption spectroscopy, and photoelectron spectroscopy (PES). In addition, planar solar cells incorporating the MAPI layers are produced. The obtained XRD data show that MAPI with high perovskite phase purity can be fabricated in a broad substrate temperature range between 75 C and 150 C. The SEM measurements show that with increasing substrate temperature the morphology of the MAPI layers undergoes significant changes which can be separated into three distinct processes, taking place simultaneously: formation of the perovskite by incorporation of MAI into the PbI 2 grains, recrystallization of the perovskite grains, and an Ostwald ripening like growth of the recrystallized grains. By the combination of the UV/VIS and in vacuo PES data, band diagrams for PbI 2 , MAI, and MAPI can be drawn which appear to be independent on the substrate temperature.

No abstract