A dominant positron capture and annihilation at vacancies in MAPbI$_3$ and CsMAFAPb(I$_x$Br$_{1-x}$)$_3$ layers on PEDOT-PPS/ITO/glass substrates

P. Aversa (1) , Minjin Kim (2) , V. Léger (1) , H. Lee (2) , D. Tondelier (2) , Olivier Plantevin (3) , J. Botsoa (4) , P. Desgardin (4) , Jean-Eric Bourée (2) , L. Liszkay (5) , M. Dickmann (6) , W. Egger (6) , M. F. Barthe (4) , Bernard Geffroy (7, 2) , C. Corbel (1)

1 LSI - Laboratoire des Solides Irradiés
2 LPICM - Laboratoire de physique des interfaces et des couches minces [Palaiseau]
3 CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse
4 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation
5 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
6 Institute of Jet Propulsion, Bundeswehr University Munich
7 LICSEN - Laboratoire Innovation en Chimie des Surfaces et NanoSciences

Hybrid inorganic-organic halide perovskitesattract much attention for their application in optoelectronic devices. However, the performancesstrongly depend on the quality of the active layers and their capacity to withstand device operation without irreversible damage [1,2]. Light illumination is reported to induce ion migration in HOIPs [3]. Applying a bias in dark in CH3NH3PbI3(MAPbI3) based solar cells also results in ion migration [4]. Dark current measurements give evidence of temperature–dependent charge transport mechanisms in MAPbI3that are respectively related to electron/hole and ion transport [5]. This questions the existenceand/orgeneration of defects in HOIPs and their role in defect-assisted mechanisms of ion migration under bias and light illumination on photovoltaïc performance. This work focuses on vacancy-type defects. When in neutral or negatively charged states, such defects capture thermalized positronsin their open volume and give rise to annihilation fingerprints specific to the nature of the vacancy-type defects. Positrons have a most striking reproducible and stable behavior in MAPbI3 and CsMAFAPb(IxBr1-x)3layers spin coated on PEDOT:PPS/ITO/glass substrates in similar conditions by solution growth process. The annihilation characteristics, e-_e+ annihilating pair momentum distribution and positron lifetime spectra, are consistent with huge native vacancy concentration, ≥3*1018cm-3, that efficientlycapture thermalized positrons before their annihilation. An additional noticeable property is that the coverage with a PCBM electron transport layer has little effect on these native vacancies. The positron annihilation lifetime in the vacancies, 334(5) ps,has been also earlier observed in sintered MAPbI3 pellets [6]. The nature of the vacancies and their stability with ageingis discussed.

Domains: Material chemistry

P. Aversa, Minjin Kim, V. Léger, H. Lee, D. Tondelier, et al.. A dominant positron capture and annihilation at vacancies in MAPbI$_3$ and CsMAFAPb(I$_x$Br$_{1-x}$)$_3$ layers on PEDOT-PPS/ITO/glass substrates. JPH 2021 - 6èmes Journées Pérovskites Halogénées, Geffroy, Bernard; Oswald, Frédéric, Mar 2021, Palaiseau, France. ⟨cea-03185871⟩