Revisiting the Determination of the Valence Band Maximum and Defect Formation in Halide Perovskites for Solar Cells: Insights from Highly Sensitive Near-UV Photoemission Spectroscopy.

ACS Appl Mater Interfaces

Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany.

Published: September 2021

Using advanced near-UV photoemission spectroscopy (PES) in constant final state mode (CFSYS) with a very high dynamic range, we investigate the triple-cation lead halide perovskite Cs(MAFA)Pb(IBr) and gain detailed insights into the density of occupied states (DOS) in the valence band and band gap. A valence band model is established which includes the parabolic valence band edge and an exponentially decaying band tail in a single equation. This allows us to precisely determine two valence band maxima (VBM) at different -vectors in the angle-integrated spectra, where the highest one, resulting from the VBM at the -point in the Brillouin zone, is found between -1.50 to -1.37 eV relative to the Fermi energy . We investigate quantitatively the formation of defect states in the band gap up to upon decomposition of the perovskites during sample transfer, storage, and measurements: during near-UV-based PES, the density of defect states saturates at a value that is around 4 orders of magnitude below the density of states at the valence band edge. However, even short air exposure, or 3 h of X-ray illumination, increased their density by almost a factor of six and ∼40, respectively. Upon prolonged storage in vacuum, the formation of a distinct defect peak is observed. Thus, near-UV CFSYS with modeling as shown here is demonstrated as a powerful tool to characterize the valence band and quantify defect states in lead halide perovskites.

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c10171DOI Listing

Publication Analysis

Top Keywords

valence band
28
defect states
12
band
10
halide perovskites
8
near-uv photoemission
8
photoemission spectroscopy
8
lead halide
8
band gap
8
band edge
8
valence
7

Similar Publications

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!