Dibyajyoti Ghosh University of Bath Perovskite Materials for

Dibyajyoti Ghosh University of Bath Perovskite Materials for Solar Cells : Atomic-scale Insights from ab initio Modelling Saiful. Islam Size Matters May 30, 2004

Talk Outline Introduction Energy : Source and Crisis Photovoltaics and Perovskite Solar Cells Metal Halide Perovskite A-cation mixing Effect on Stability Change in Dynamics Lead Free materials Sn-Ge Mixing: Stability and Optoelectronics Dibyajyoti Ghosh Eo. Co. E-2018

Energy London Berlin Paris New York Dibyajyoti Ghosh Eo. Co. E-2018

Energy Crisis http: //theameri canenergynew s. com oursolarenergy. com Dibyajyoti Ghosh Eo. Co. E-2018

Environmental Effect Dibyajyoti Ghosh Eo. Co. E-2018

Renewable and Green Energy Dibyajyoti Ghosh Eo. Co. E-2018

Renewable and Green Energy Share In UK (2016 -17) www. gov. uk/government/collections/renewables-statistics Dibyajyoti Ghosh Eo. Co. E-2018

Solar Cells Absorb sunlight Separate the charge carriers Extract the carriers Dibyajyoti Ghosh Eo. Co. E-2018

Materials for Solar Cells www. nrel. gov/pv/ Dibyajyoti Ghosh Eo. Co. E-2018

Perovskites : Structure Chemical Formula: ABX 3 A = Monovalent cation B = Divalent metal X = Monovalent anion Dibyajyoti Ghosh Eo. Co. E-2018

Organic-Inorganic Perovskite Methylammonium lead iodide CH 3 NH 3 Pb. I 3 Easy synthesis Tune absorption Long diffusion length Pb. I 6 octahedra CH 3 NH 3 + Eames et. al. Nature Comm. 2015, 6, 7497 Dibyajyoti Ghosh Eo. Co. E-2018

Perovskite Solar Cells Sunlight Glass or Plastic Ti-oxide Perovskite h+e Back Contact Dibyajyoti Ghosh Eo. Co. E-2018

Promising Material: But …. Imperial College, London Degradation under ambient conditions Ion migration Eames et. al. Nature Comm. 2015, 6, 7497 Lead Toxicity Upscaling and Reproducibility Dibyajyoti Ghosh Eo. Co. E-2018

Dynamic Lattice FAPb. I 3 Dynamics: Ø Periodic octahedral tilting Ø Tumbling and libration of organic cations Weller et. al. , J. Phys. Chem. Lett (2015) Quarti et. al. , Phys. Chem. Phys. (2015) Effects : Ø Dynamic band-gap Motta et. al. , Nat. Commun (2015) Ø PL efficiency, excited state dynamics Park et. al. , Nano Lett (2017) Dibyajyoti Ghosh Eo. Co. E-2018

Stability and Dynamics of Perovskites Compositional Engineering Dibyajyoti Ghosh Eo. Co. E-2018

Cation Mixing: Increased Stability BX 6 MAPb. I 0. 6 Br 0. 4 FA 0. 83 Cs 0. 17 Pb. I 0. 6 Br 0. 4 Mc. Meekin et. al. , Science (2016) Possible reasons : Ø Higher dipole interactions Ø Increased entropy of mixing Binek et. al. , J. Phys. Chem. Lett. (2015) Yi et. al. , Energy Environ. Sci. , (2016) Dibyajyoti Ghosh Eo. Co. E-2018

Key Questions : Mixed A-cation Perovskites Effect on overall structure ? Origin of enhanced stability ? Effect of the structural dynamics ? Which System ? FAPb. I 3 as the parent compound Dibyajyoti Ghosh Eo. Co. E-2018

Methods Method : ab initio molecular dynamics On-the-fly calculation of forces from DFT Solve Newtonian EOM for moving atomic nuclei Simulation Parameters: Supercell with 768 atoms for FAPb. I 3 (~ 26 k. AU/ps) NPT simulations at 300 K using Nose-Hoover thermostat Time step of 1 fs to capture motion of H-atoms PBEsol functional with DZVP basis set, GTH pseudopotentials, DFT-D 3 for dispersion Dibyajyoti Ghosh Eo. Co. E-2018

Mixed Cation Perovskites: Overall Structure and Stability Dibyajyoti Ghosh Eo. Co. E-2018

A-site Cation Mixing: Structural Trends Volume reduction with mixing of small cations Dibyajyoti Ghosh Eo. Co. E-2018

Tilting of Octahedra FA 0. 9 Rb 0. 1 FA 0. 97 Rb 0. 03 FA 0. 9 Cs 0. 1 FA 0. 97 Cs 0. 03 FA 0. 8 MA 0. 1(Cs. Rb)0. 1 FA 0. 8 MA 0. 1 Cs 0. 1 FA 0. 97 MA 0. 03 FA Tilting of Octahedron θ FA 0. 9 Cs 0. 1 Volume reduction with mixing of small cations FAPI Dibyajyoti Ghosh Eo. Co. E-2018

Stronger Hydrogen Bonding : Stability Effect ? FA 0. 9 Cs 0. 1 Pb. I 3 Octahedra tilting I---H-N hydrogen bonds Increased H-bond strength Red-shift in N-H stretching Structural stability Matsui et. al. , Adv. Mater. , (2017) Dibyajyoti Ghosh Eo. Co. E-2018

Mixed Cation Perovskites: Dynamical Property Dibyajyoti Ghosh Eo. Co. E-2018

Change in Dynamics : Locked Octahedra Tilting FA 0. 9 Cs 0. 1 Pb. I 3 FAPb. I 3 Smaller fluctuation in Pb-I-Pb angle : more monochromatic light absorption Amat et. al. , Nano Lett. , (2014) Dibyajyoti Ghosh Eo. Co. E-2018

Change in FA-cation Dynamics FAPb. I 3 FA 0. 9 Cs 0. 1 Pb. I 3 N N Restricted tumbling motion with mixing Good Vibrations: Locking of Octahedral Tilting in Mixed-Cation Iodide Can affect the carrier life-time Perovskites for Solar Cells D. Ghosh, P. Huang et. W. Atkins, M. S. Islam, A. Walker, C. Eames, al. , J. Mater Chem. A , (2017) Kubicki et. al. , J. Am. Chem. Soc. , (2017) ACS Energy Lett. 2017, 2, 2424– 2429 Dibyajyoti Ghosh Eo. Co. E-2018

Lead Toxicity: Lead-free hybrid perovskites Dibyajyoti Ghosh Eo. Co. E-2018

Lead Toxicity : Other B-metals ? BX 6 MABI 3 B = Sn, Ge Dibyajyoti Ghosh Eo. Co. E-2018

Lead Free B-site : Sn-Ge Mixing Stability Ge-content MAGe. I 3 MASn. I 3 Electronic Property Ge-content Lead-Free Perovskite Semiconductors Based on Germanium–Tin Solid Solutions: Structural and Optoelectronic Properties N. Nagane, D. Ghosh, R. L. Z. Hoye, B. Zhao, S. Ahmad, A. B. Walker, M. S. Islam, S. Ogale, and A. Sadhanala J. Phys. Chem. C, 2018, 122, 5940– 5947 Dibyajyoti Ghosh Eo. Co. E-2018

Concluding Remarks Dibyajyoti Ghosh Eo. Co. E-2018

Summary v Atomic-scale insights into cation and B-metal mixing v Increased H-bonding: enhanced stability v Reduced dynamics: Can affect PV-behaviour v Lead-free Perovskite materials for solar cells: stable and good optoelectronic properties Dibyajyoti Ghosh Eo. Co. E-2018

Recent Work at Bath O 2/light degradation (2017) Light soaking + O 2/H 2 O (2017) Compositional Engineering (2017) Ion-migration (2016 -17) Dibyajyoti Ghosh Eo. Co. E-2018

Thanks to… Dibyajyoti Ghosh Eo. Co. E-2018

Group & Collaboration Prof. A. B. Walker Prof. M. S. Islam Eo. Co. E for funding All Collaborators Archer HPC and Balena HPC Dibyajyoti Ghosh Eo. Co. E-2018

Publications 1. “Phase Behaviour and Polymorphism of Formamidinium Lead Iodide”, O. J. Weber, D. Ghosh, S. Gaines, P. F. Henry, A. B. Walker, M. S. Islam and M. T. Weller (Under review in Chem. Mater. ) 2. “Lead Free Germanium-Tin Solid Solutions Based Perovskite Semiconductors: Structural and Optoelectronic Properties”, S. Nagane, D. Ghosh, R. Hoye, B. Zhao, S. Ahmad, A. B. Walker, M. S. Islam, S. Ogale and A. Sadhanala, J. Phys. Chem. C 2018, 122, 5940– 5947 3. “Formamidinium-Caesium Mixed Perovskites : Structural and Optoelectronic Effects of Chemical Pressure through Cation-Size Mismatch”, D. Ghosh, A. R. Smith, A. B. Walker and M. S. Islam (Submitted) 4. “Good Vibrations: Locking of Octahedral Tilting in Mixed-Cation Iodide Perovskites for Solar Cells”, D. Ghosh, P. W. Atkins, M. S. Islam, A. B. Walker and C. Eames, ACS Energy Lett. , 2017, 2, 2424 5. “Azetidinium lead iodide for perovskite solar cells”, S. R. Pering, W. Deng, J. R. Troughton, P. Kubiak, D. Ghosh, R. G Niemann, F. Brivio, F. E. Jeffrey, A. B. Walker, M. S. Islam, T. M. Watson, P. R. Raithby, A. L. Johnson, S. E. Lewis, P. J. Cameron, J. Mater. Chem. A, 2017, 5, 20658 Dibyajyoti Ghosh Eo. Co. E-2018

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Dibyajyoti Ghosh Eo. Co. E-2018

Dibyajyoti Ghosh Eo. Co. E-2018

Pb. I 6 Octahedra Volume of Octahedron Pb-I No volume contraction of Pb. I 6 Dibyajyoti Ghosh Eo. Co. E-2018

Solar Cells Solar cells: converts the energy of light directly into electricity by the photovoltaic effect wikipedia. org Dibyajyoti Ghosh Eo. Co. E-2018

Single-Junction Photovoltaics Dibyajyoti Ghosh Eo. Co. E-2018

Why Perovskite Solar Cells? Dibyajyoti Ghosh Eo. Co. E-2018

BOMD Dibyajyoti Ghosh Eo. Co. E-2018