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Ionic transport in hybrid lead iodide perovskite solar cells.

Eames C, Frost JM, Barnes PR, O'Regan BC, Walsh A, Islam MS - Nat Commun (2015)

Bottom Line: Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear.Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current-voltage response of a perovskite-based solar cell.We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Bath, Bath BA2 7AY, UK.

ABSTRACT
Solar cells based on organic-inorganic halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behaviour such as current-voltage hysteresis and a low-frequency giant dielectric response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and experimental study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.

No MeSH data available.


Related in: MedlinePlus

Transport mechanisms in the CH3NH3PbI3 perovskite structure.Schematic illustration of the three ionic transport mechanisms involving conventional vacancy hopping between neighbouring positions: (a) I− migration along an octahedron edge; Pb2+ migration along the diagonal direction <110>; (b) CH3NH3+ migration into a neighbouring vacant A-site cage involving motion normal to the unit cell face composed of four iodide ions.
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f2: Transport mechanisms in the CH3NH3PbI3 perovskite structure.Schematic illustration of the three ionic transport mechanisms involving conventional vacancy hopping between neighbouring positions: (a) I− migration along an octahedron edge; Pb2+ migration along the diagonal direction <110>; (b) CH3NH3+ migration into a neighbouring vacant A-site cage involving motion normal to the unit cell face composed of four iodide ions.

Mentions: In this study, three vacancy transport mechanisms involving conventional hopping between neighbouring positions (illustrated in Fig. 2) were considered. These were (i) I− migration along an octahedron edge; (ii) Pb2+ migration along the diagonal (<110> directions) of the cubic unit cell; (iii) CH3NH3+ migration into a neighbouring vacant A-site cage. Energy profiles for these mechanisms were mapped out by performing a series of transition-state calculations between adjacent equivalent sites. Particular care has to be taken to ensure the starting and end point configurations are well converged to avoid anomalously low migration energies. This approach allows the energy barrier to ion migration to be determined, and has been used successfully in previous studies on oxide-ion, proton and metal-ion migration in perovskite oxides5254. One particular challenge is to adequately describe the polarization response to the change in position of the migrating ion, which involves a combination of electronic polarization and lattice relaxation; this required the large supercells employed here to minimize any spurious interactions.


Ionic transport in hybrid lead iodide perovskite solar cells.

Eames C, Frost JM, Barnes PR, O'Regan BC, Walsh A, Islam MS - Nat Commun (2015)

Transport mechanisms in the CH3NH3PbI3 perovskite structure.Schematic illustration of the three ionic transport mechanisms involving conventional vacancy hopping between neighbouring positions: (a) I− migration along an octahedron edge; Pb2+ migration along the diagonal direction <110>; (b) CH3NH3+ migration into a neighbouring vacant A-site cage involving motion normal to the unit cell face composed of four iodide ions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4491179&req=5

f2: Transport mechanisms in the CH3NH3PbI3 perovskite structure.Schematic illustration of the three ionic transport mechanisms involving conventional vacancy hopping between neighbouring positions: (a) I− migration along an octahedron edge; Pb2+ migration along the diagonal direction <110>; (b) CH3NH3+ migration into a neighbouring vacant A-site cage involving motion normal to the unit cell face composed of four iodide ions.
Mentions: In this study, three vacancy transport mechanisms involving conventional hopping between neighbouring positions (illustrated in Fig. 2) were considered. These were (i) I− migration along an octahedron edge; (ii) Pb2+ migration along the diagonal (<110> directions) of the cubic unit cell; (iii) CH3NH3+ migration into a neighbouring vacant A-site cage. Energy profiles for these mechanisms were mapped out by performing a series of transition-state calculations between adjacent equivalent sites. Particular care has to be taken to ensure the starting and end point configurations are well converged to avoid anomalously low migration energies. This approach allows the energy barrier to ion migration to be determined, and has been used successfully in previous studies on oxide-ion, proton and metal-ion migration in perovskite oxides5254. One particular challenge is to adequately describe the polarization response to the change in position of the migrating ion, which involves a combination of electronic polarization and lattice relaxation; this required the large supercells employed here to minimize any spurious interactions.

Bottom Line: Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear.Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current-voltage response of a perovskite-based solar cell.We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Bath, Bath BA2 7AY, UK.

ABSTRACT
Solar cells based on organic-inorganic halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behaviour such as current-voltage hysteresis and a low-frequency giant dielectric response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current-voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and experimental study suggest that hybrid halide perovskites are mixed ionic-electronic conductors, a finding that has major implications for solar cell device architectures.

No MeSH data available.


Related in: MedlinePlus