Enhanced Optical Absorption via Mixed-Valent Doping of A3B2X9 Triple Perovskites

Published in Chemical Science. Open-access article available here:
https://doi.org/10.1039/D1SC03775G

Find the YouTube version of this talk here: https://bit.ly/2U5YgLf

If you're interested in this work, please check out our open-access review on perovskite-inspired materials and defect tolerance here:
https://iopscience.iop.org/article/10.1088/1361-6528/abcf6d

For other research articles see:
https://bit.ly/3pBMxOG

For other talks on YouTube see:
https://bit.ly/2U5YgLf

Transcript

1. Enhanced Optical Absorption via Mixed-Valent Doping of A3 B2 X9 Triple Perovskites Seán R. Kavanagh, Chantalle Krajewska, Lina Zhang, Dominik Kubicki, Krishanu Dey, Sam Stranks, David O. Scanlon, Aron Walsh, Robert G. Palgrave sean.kavanagh.19@ucl.ac.uk
2. Perovskite-Inspired: Vacancy-Ordered Triple Perovskites AIBIIX3 AI 3 B2 IIIX9 = AI(00B2 III)1/3 X3 (Cubic CsPbBr3 ) (Cs3 Bi2 Br9 ) Cation Substitution 1. Huang, Y.-T., Kavanagh, S. R., Scanlon, D. O., Walsh, A. & Hoye, R. L. Z. Perovskite-Inspired Materials for Photovoltaics -- From Design to Devices. 2021 Nanotechnology 32 132004
3. ✅ Non-Toxic ✅ Low-Temperature, Solution-based Synthesis ✅ Air-Stable1,2 ✅ Long Charge-Carrier Lifetimes1 ❌ Large Bandgaps (> 2 eV) Eg, ideal = ~2 eV (Indoor PV); 1.7-1.9 eV (Tandem top-cells) Perovskite-Inspired: Vacancy-Ordered Triple Perovskites AI 3 B2 IIIX9 = AI(00B2 III)1/3 X3 (Cs3 Bi2 Br9 ) 1. Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh and R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004. 2. S. R. Kavanagh* & Z. Li* et al., J. Mater. Chem. A, 2020, 8, 21780–21788. 3. D. Ju, X. Jiang, H. Xiao, X. Chen, X. Hu and X. Tao, J. Mater. Chem. A, 2018, 6, 20753–20759.
4. Group: 14 15 n = 5 n = 6 Strategy: Heterovalent Doping Can We Tune Their Optical Absorption through Doping?
5. x 0 1 2 Fermi Level (eV) -0.50 -0.25 0.00 0.25 0.50 Formation Energy (eV) ε(+1/-1) SnBi SnBi SnBi SnBi Sn:Cs3 Bi2 Br9 – Isolated SnBi Substitution
6. Sn:Cs3 Bi2 Br9 – SnBi Clustering 6 8 10 12 SnBi - SnBi Separation [Å] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Formation Energy [eV] Nearest-Neighbour Coordination ΔHf([SnBi-SnBi]×) ΔHf(Sn Bi) + ΔHf(SnBi), Isolated ΔHf(Sn× Bi) + ΔHf(Sn× Bi), Isolated
7. Sn:Cs3 Bi2 Br9 – SnBi Clustering x 0 1 2 Fermi Level (eV) -0.50 -0.25 0.00 0.25 0.50 Formation Energy (eV) ε(+1/-1) SnBi SnBi SnBi SnBi
8. Sn:Cs3 Bi2 Br9 – SnBi Clustering 0 1 2 3 Fermi Level (eV) 0.0 0.8 1.6 2.4 Formation Energy (eV) E F ε(+2/0) ε(+2/0) ε(0/-2) ε(0/-2) (Sn Bi -Sn Bi ) (Sn Bi -V Cs ) (Sn Bi -V Bi ) (Sn Bi -V Br )
9. − 1 0 1 2 Energy(eV) Density of States Total DOS Bi (s) Bi (p) Br (p) Sn (s) (SnBi -SnBi )0 => (SnIV Bi – SnII Bi )0 − 1 0 1 2 Energy(eV) Total DOS Sn (s) Sn (p) SnIV Bi +1 SnII Bi -1 Density of States Orbital-Projected DOS Site-Projected DOS Sn:Cs3 Bi2 Br9 – SnBi Clustering
10. − 1 0 1 2 Energy(eV) Density of States Total DOS Bi (s) Bi (p) Br (p) Sn (s) (SnBi -SnBi )0 -> (SnIV Bi – SnII Bi )0 Orbital-Projected DOS Sn:Cs3 Bi2 Br9 – SnBi Clustering
11. − 1 0 1 2 Energy(eV) Density of States Total DOS Bi (s) Bi (p) Br (p) Sn (s) From SnII Bi – SnIV Bi à (SnII Bi – SnIII Bi )- + h+ VB E = 2.60 eV à (SnIII Bi – SnIV Bi )+ + e- CB E = 2.15 eV à SnIII Bi – SnIII Bi E = 1.72 eV Sn:Cs3 Bi2 Br9 – Optical Transitions
12. SnII Bi – SnIV Bi àSnIII Bi – SnIII Bi Eabs = 1.72 eV Sn:Cs3 Bi2 Br9 – Intervalence Charge Transfer (IVCT) −1 0 1 2 3 Configuration Coordinate (ΔQ) [amu1/2Å] 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Relative Energy [eV] 1.39 eV 0.33 eV 1.72 eV
13. 3 0 1 2 Energy(eV) Absorbance Experimental Spectrum w/ Band Edge Subtracted Sn:Cs3 Bi2 Br9 – Optical Transitions − 1 0 1 2 Energy(eV) Density of States Total DOS Bi (s) Bi (p) Br (p) Sn (s)
14. Roy et al. J. Phys. Chem. C, 2020, 124, 36, 19484-19491 Ju et al. J. Mater. Chem. A, 2018, 6, 20753 Lindquist et al. Chem. Sci., 2019,10, 10620-10628 Pb-doped Cs3 Bi2 Br9 : ⇾ PbBi + VBr ⇾ Eg ↓ (2.60 to 2.23 eV) Sn-doped Ma3 Sb2 I9 : ⇾ Sn(II) ⇾ Eg ↓ ↓ (Red -> Black) Sn-doped Cs2 AgBiBr6 : ⇾ Sn(II) and Sn(IV) ⇾ Eg ↓ ↓ (Red -> Black)
15. Ju et al. J. Mater. Chem. A, 2018, 6, 20753 Lindquist et al. Chem. Sci., 2019,10, 10620-10628 0 1 2 3 Fermi Level (eV) 0.0 0.8 1.6 2.4 Formation Energy (eV) E F ε(+2/0) ε(+2/0) ε(0/-2) ε(0/-2) (Sn Bi -Sn Bi ) (Sn Bi -V Cs ) (Sn Bi -V Bi ) (Sn Bi -V Br ) − 1 0 1 2 Energy(eV) Density of States Total DOS Bi (s) Bi (p) Br (p) Sn (s)
16. Sn doping produces a mixed-valence complex with strong, broad visible light absorption, with unusual long-term stability. Mixed valency doping can provide a powerful technique to tune the optical properties of lead-free perovskites. Sn:Cs3 Bi2 Br9 – Conclusions @Kavanagh_Sean_ kavanase sean.kavanagh.19@ucl.ac.uk