TY  - JOUR
A1  - Zu, Fengshuo
A1  - Wolff, Christian Michael
A1  - Ralaiarisoa, Maryline
A1  - Amsalem, Patrick
A1  - Neher, Dieter
A1  - Koch, Norbert
T1  - Unraveling the Electronic Properties of Lead Halide Perovskites with Surface Photovoltage in Photoemission Studies
T2  - ACS applied materials & interfaces
N2  - The tremendous success of metal-halide perovskites, especially in the field of photovoltaics, has triggered a substantial number of studies in understanding their optoelectronic properties. However, consensus regarding the electronic properties of these perovskites is lacking due to a huge scatter in the reported key parameters, such as work function (Φ) and valence band maximum (VBM) values. Here, we demonstrate that the surface photovoltage (SPV) is a key phenomenon occurring at the perovskite surfaces that feature a non-negligible density of surface states, which is more the rule than an exception for most materials under study. With ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe, we evidence that even minute UV photon fluxes (500 times lower than that used in typical UPS experiments) are sufficient to induce SPV and shift the perovskite Φ and VBM by several 100 meV compared to dark. By combining UV and visible light, we establish flat band conditions (i.e., compensate the surface-state-induced surface band bending) at the surface of four important perovskites, and find that all are p-type in the bulk, despite a pronounced n-type surface character in the dark. The present findings highlight that SPV effects must be considered in all surface studies to fully understand perovskites’ photophysical properties.
KW  - lead halide perovskite films
KW  - ultraviolet photoelectron spectroscopy
KW  - Kelvin probe
KW  - surface band bending
KW  - surface photovoltage
KW  - surface states
Y1  - 2019
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/49014
SN  - 1944-8244
SN  - 1944-8252
VL  - 11
IS  - 24
SP  - 21578
EP  - 21583
PB  - American Chemical Society
CY  - Washington
ER  -