Charge Trapping in Photovoltaically Active Perovskites and Related Halogenoplumbate Compounds

Abstract

Halogenoplumbate perovskites (MeNH₃PbX₃, where X is I and/or Br) have emerged as promising solar panel materials. Their limiting photovoltaic efficiency depends on charge localization and trapping processes that are presently insufficiently understood. We demonstrate that in halogenoplumbate materials the holes are trapped by organic cations (that deprotonate from their oxidized state) and Pb²⁺ cations (as Pb³⁺ centers), whereas the electrons are trapped by several Pb²⁺ cations, forming diamagnetic lead clusters that also serve as color centers. In some cases, paramagnetic variants of these clusters can be observed. We suggest that charge separation in the halogenoplumbates resembles latent image formation in silver halide photography. Electron and hole trapping by lead clusters in extended dislocations in the bulk may be responsible for accumulation of trapped charge observed in this photovoltaic material.