Photophysics of Localized Deep Defect States in Hybrid Organic–Inorganic Perovskites

Abstract

Hybrid organic−inorganic halide perovskites have sub-band-gap absorption and photocurrent spectra which are difficult to explain using existing models, particularly in light of the small Urbach energies of the intraband absorption edges. Here, we show that the sub-band-gap optical transitions are mediated by bistable amphoteric native defects and a single localized acceptor-like defect strongly coupled to the local lattice vibrations. The coupling is very well accounted for by configuration coordinate diagrams for the defect and for the conduction and the valence band states. The model identifies the common origin of, and uses a single set of parameters to explain, the intricate and very broad bipolar photocurrent spectra found in MAPb(I 1−x Br x ) 3 alloy based photovoltaic (PV) devices, the featureless monopolar photocurrent in MAPbI 3 , and the broad infrared photoluminescence in MAPBr 3 films. In addition, the same deep acceptor defect facilitates, via a multistep process, thermally activated nonradiative recombination of the photoexcited electrons and holes.

Facile Preparation of Large-Area, Ultrathin, Flexible Semi-Transparent Perovskite Solar Cells via Spin-Coating

“…Of course, one could expect such a shift in the case of very thin samples (as it can be related to quantum confinement and built-in strain), but here it was clearly observed in the whole investigated thickness range. Another possible explanation is related to the hypothesis that emission in HOIPs such as MAPbI 3 is governed by bistable amphoteric native defects (BANDs), i.e., defects whose nature (donor/acceptor) and formation energy are controlled by the location of Fermi energy. , Assuming that due to the increased surface-to-volume ratio in thinner films, the concentration of BANDs is higher, one can expect such a behavior of the PL peak. A further interesting feature in PL spectra is related to the thickness range between 50 and 225 nm.…”

Facile Preparation of Large-Area, Ultrathin, Flexible Semi-Transparent Perovskite Solar Cells via Spin-Coating

“…defects whose nature (donor/acceptor) and formation energy are controlled by the location of Fermi energy. 42,43 Assuming that due to increased surface to volume ratio in thinner films the concentration of BANDs is higher one can expect such a behavior of PL peak. A further interesting feature in PL spectra is related to the thickness range between 50 nm and 225 nm.…”

Challenges and Perspectives toward Future Wide‐Bandgap Mixed‐Halide Perovskite Photovoltaics

“…Subsequent work further explained these experimental results by establishing a model of a single acceptor‐like defect with the transition near VBM, which is associated with the I i /Br i defects acting as nonradiative recombination centers. [ 48 ] Note that the cation substitution in WBG perovskites was proved not to significantly affect defect activities, whereas the cation‐ or Br‐induced lattice deformation would make the defects optoelectronically active as the bandgap opens. [ 49 ] By employing near‐field scanning tunneling microscopy (STM), detailed atomic arrangement, especially the X‐site locations, in I/Br‐mixed WBG perovskites was clarified.…”