Substrate-controlled band positions in CH₃NH₃PbI₃perovskite films

Abstract

Using X-ray and ultraviolet photoelectron spectroscopy, the surface band positions of solution-processed CH3NH3PbI3 perovskite thin films deposited on an insulating substrate (Al2O3), various n-type (TiO2, ZrO2, ZnO, and F:SnO2 (FTO)) substrates, and various p-type (PEDOT:PSS, NiO, and Cu2O) substrates are studied. Many-body GW calculations of the valence band density of states, with spin-orbit interactions included, show a clear correspondence with our experimental spectra and are used to confirm our assignment of the valence band maximum. These surface-sensitive photoelectron spectroscopy measurements result in shifting of the CH3NH3PbI3 valence band position relative to the Fermi energy as a function of substrate type, where the valence band to Fermi energy difference reflects the substrate type (insulating-, n-, or p-type). Specifically, the insulating- and n-type substrates increase the CH3NH3PbI3 valence band to Fermi energy difference to the extent of pinning the conduction band to the Fermi level; whereas, the p-type substrates decrease the valence band to Fermi energy difference. This observation implies that the substrate's properties enable control over the band alignment of CH3NH3PbI3 perovskite thin-film devices, potentially allowing for new device architectures as well as more efficient devices.

Control of Interface Defects for Efficient and Stable Quasi‐2D Perovskite Light‐Emitting Diodes Using Nickel Oxide Hole Injection Layer

“…We observe that the Fermi levels for the 15, 35, and 120 nm thick perovskite films deposited on PEDOT:PSS (5.02, 5.05, and 5.15 eV, respectively) were strongly influenced by the WF of the PEDOT:PSS (measured at 5.00 eV), i.e., the Fermi level of the perovskite was “pulled” toward that of PEDOT:PSS 40, 41. This implies that the depletion width of the perovskites on PEDOT:PSS extended through the bulk of the film 42.…”

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

“…On ptype substrates, such as PEDOT:PSS, NiO and Cu 2 O, the Fermi level of MAPbI 3 shifts closer to mid-gap. 185 These examples show the importance of characterizing the absorbers on the charge transport layers they would be paired with and to report the substrate with the PES measurements. Sample degradation during photoemission spectroscopy measurements Evaluating the degree of degradation during the measurements when characterizing these soft materials has been demonstrated to be crucial for a robust and accurate analysis of the properties described above.…”

Ionic Reactivity at Contacts and Aging of Methylammonium Lead Triiodide Perovskite Solar Cells

“…[23] The use of other contact materials of diverse electronic character (either n-or p-type, and insulating) have revealed that the Fermi level within MAPbI 3 is strongly influenced by the substrate conductivity type. [24] In connection with the electronic interfacial properties, recent electrical measurements have shown that the potential drop concentrates near the TiO 2 /MAPbI 3 contact forming a sort of p-n junction. [25,26] But interfaces evolve during solar cell operation, presumably by the presence of moving ions, in such a way that the connection between photoemission spectroscopy findings and the reported V J − distortions needs of complementary analysis.…”

“…Interfacial electronic properties as energy level alignment constitute a relevant piece of knowledge that can be addressed through photoemission spectroscopies. [23,24] From these works several recommendations for proper interface engineering are extracted. It is recognized that spiro-OMeTAD exhibits a non-optimum energy level alignment at interfaces with perovskite absorbers, while the TiO 2 conduction band is in relatively fair energy alignment.…”