Azmat Ali1,Fredrik Johansson1,2,Mariam Ahmad3,Hervé Cruguel1,Erika Giangrisostomi4,Ruslan Ovsyannikov4,Lenart Dudy5,Mathieu Silly5,Morten Madsen3,Emmanuel L'Huillier1,Nadine Witkowski1
Sorbonne Université1,KTH Royal Institute of Technology2,University of Southern Denmark3,Institute for Methods and Instrumentation in Synchrotron Radiation Research4,Synchrotron SOLEIL5
Azmat Ali1,Fredrik Johansson1,2,Mariam Ahmad3,Hervé Cruguel1,Erika Giangrisostomi4,Ruslan Ovsyannikov4,Lenart Dudy5,Mathieu Silly5,Morten Madsen3,Emmanuel L'Huillier1,Nadine Witkowski1
Sorbonne Université1,KTH Royal Institute of Technology2,University of Southern Denmark3,Institute for Methods and Instrumentation in Synchrotron Radiation Research4,Synchrotron SOLEIL5
Understanding of electronic band structure and charge carrier dynamics of halide perovskites and their interface is critical for the advancement of perovskite photovoltaics[1,2]. Inorganic Cesium lead bromide (CsPbBr<sub>3</sub>) perovskite nanocrystals (NCs) with a bandgap of 2.3 eV are regarded as one of the potential candidates as an active layer in solar cells devices, thanks to significant progress made recently in terms of improving its intrinsic properties and stability under environmental conditions. However, stability under UV and X-ray exposure remains an open question[3-6]. The stability of spin-coated CsPbBr<sub>3</sub> NCs deposited on gold (Au) substrates is investigated here under the impact of the UV laser light and X-rays. Under the UV laser pulse, the NCs exhibit distinctly different behavior depending upon the energy of the laser pulse, its fluence and time NCs exposed to it. When the NCs are exposed to UV laser pulses with the photon energy of 3.6 eV (greater than the bandgap), the NCs are modified irreversibly. Both metallic lead and ionic lead with a new component of Pb4f are detected in the Pb4f core-level spectra. Similarly, when NCs exposed exclusively to X-ray with high flux, same components of Pb4f were found in Pb4f spectrum. The modification is more or less similar in either case; however, under UV laser exposure, a large chemical shift of 0.69 eV towards higher binding energy observed after the exposure, which is not the case with X-ray exposure alone. The chemical shift could be attributed to the accumulation of charge carriers at the interface under UV laser and getting trapped by the metallic lead (donor-type surface states) [6]. Therefore, depending on the type of radiation exposure either UV laser or X-rays, the CsPbBr<sub>3</sub> NCs show different behavior and thus the energy level alignments. We show that the chemical properties of NCs are sensitive to UV laser and X-rays irradiation, and investigation of these changes under the type of radiation exposure might help us understand the underlying phenomenon that governs these changes.