Non-radiative Carrier Recombination Enhanced by Lone-pair Formation in Kesterite Solar Cells

Non-radiative Carrier Recombination Enhanced by Lone-pair Formation in Kesterite Solar Cells.
Theoretical Maximum Efficiency of Kesterite Solar Cells predicted by First-principles DFT calculations.

Transcript

1. Non-radiative Carrier Recombination Enhanced by Lone-pair Formation in Kesterite Solar Cells Sunghyun Kim, Ji-Sang Park, Samantha N. Hoods and Aron Walsh Dept. of Materials, Imperial College London, UK sunghyun.kim@imperial.ac.uk | frssp.github.io | frssp | 0000-0001-5072-6801 2018 – EU Kesterite Workshop ACS Energy Lett. 3, 496 (2018) arXiv:1810.11259
2. Acknowledgement 2 Prof. Aron Walsh Dr. Ji-Sang Park Dr. Samantha N. Hood
3. We Can Mitigate Climate Change. 3
4. Our Secret Weapon: Kesterite Solar Cells 4 Science 352, aad4424 (2016) Energy & Environmental Science 8, 1200 (2015)
5. It’s not working well… 5 Science 352, aad4424 (2016)
6. Is the S-Q Limit a False Promise? No. 6 Shockley, W. & Queisser, J. Appl. Phys. 32, 510 (1961) f = 100%: Only radiative recombination is possible. What is the fundamental limit of f for a certain material?
7. A Half Answer to the Quantum Efficiency f 7 Shockley, W. & W T Read, J., Phys. Rev. 87, 835 (1952), Hall, R. N., Phys. Rev. 87, 387–387 (1952).
8. Key Three Parameters: How Deep, How Large and How Many Experiment: DLTS Activation energy Cross section Concentration 8 Simulation: DFT ☑ Activation energy ☑ Cross section ☑ Concentration Henry, C. H. & Lang, D. V., Phys. Rev. B 15, 989 (1977) Shi, L. & Wang, L.-W., Phys. Rev. Lett. 109, 245501 (2012) Alkauskas, A. et al., Phys. Rev. B 90, 075202 (2014) We calculated the new theoretical maximum efficiency limited by SRH process beyond radiative limit via first-principles DFT calculations.
9. Theory in a Nutshell 9 Non-radiative carrier capture SRH limited maximum efficiency Fermi’s Golden rule: Γ"# = %& ℏ ( )* + %, Conduction band Valence band e− D+ D0 ΔE ΔQ ℏω f ℏω i ξ im ξ fn Q E elastic +E electronic E electronic D++e− D0 Electron capture barrier Phys. Rev. B 90, 075202 (2014) - . = -/0 + -2 1 − exp ⁄ . 9:; −<=>?@ (.)C S-Q limit (f=100%) SRH recombination rate REFG = np − nI % J + JK LM NO + P + PK LQ NO e/h capture coefficient Defect concentration Phys. Rev. 87, 835 (1952), Phys. Rev. 87, 387 (1952) J. Appl. Phys. 32, 510 (1961)
10. Caution and Limitation 10 Yet, we have not considered • All native points defects (e.g. interstitials), • Scattering and Recombination due to interfaces, grain boundaries, stacking fault and secondary phases, • Cation disorder, and • Deviations from thermal equilibrium. Take our results as the upper limit of true maximum values achievable in the real world.
11. Two Common Characteristics of “Killer” Centers Deep level Large lattice distortion “… So-called killer centers, with fast nonradiative transitions, … we list four examples: … 2. Defect with favorable vibrational properties, that is, with large-amplitude modes promoting the transitions, and large-energy modes to take up the electronic energy …” - A. M. Stoneham in Defects and Defect Processes in nonmetallic Solids Phys. Rev. 87, 835 (1952), Phys. Rev. 87, 387–387 (1952) Park, J.-S., Kim, S., Xie, Z. & Walsh, A., Nat. Rev. Mater. 3, 194–210 (2018) 11
12. What’s Wrong with a Lone-pair? 12 Deep level Large lattice distortion 1+ 2+ 4+ 1+ Conduction band 1+ 2+ 1+ 2+ e− e− Sn(IV): 5s05p0 (CZTS, SnS 2 ) Sn(II): 5s25p0 (SnS) Sn(IV) Sn(II) Zn Cu Cu Cu Cu Zn The lone-pair formation in a defect would lead to both deep level and large lattice distortion. Kim, S. et al., ACS Energy Lett. 3, 496 (2018)
13. Lone-pairs in VS , VS -CuZn and SnZn V S 1+ V S 1+ Cu Zn 1− Sn Zn 1+ (V S -Cu Zn )0 V S 1+ Sn Zn 1+ (a) (b) (c) Defect wave functions are well localized around Sn 5s orbitals. arXiv:1810.11259 13
14. Deep Donor Levels of VS , VS -CuZn and SnZn SnZn (2+/1+) SnZn (1+/0) VS -CuZn (0/1−) VS (1+/0) arXiv:1810.11259 14
15. Large Lattice Distortions of VS , VS -CuZn and SnZn The large lattice distortions lead to the small carrier capture barriers. ΔQ offset indicates the degree of lattice distortion. ΔQ Neutral trap Repulsive trap Giant trap V S -Cu Zn 1+ V S 2+ Sn Zn 1+ Sn Zn 2+ Cu Sn 1− 1000/T (1/K) σn (cm2) 0 2 4 6 8 10 10−30 10−27 10−24 10−21 10−18 10−15 10−12 (a ) (b Configuration Coordinate Capture cross section arXiv:1810.11259 15
16. Theoretical Maximum Efficiency Reexamined 16 S-poor S-rich Zn-rich Cu-poor p0 ZnCu CuZn Sn Zn V S V S -Cu Zn VCu EF,p EF,n EF VCu CuZn VS SnZn VS -CuZn Concentration (cm-3) Energy (eV) JSC (mA/cm2) VOC (V) SRH limited S-Q limit Best CZTS* JSC 28.97 mA/cm2 28.97 mA/cm2 21.74 mA/cm2 VOC 0.80 V 1.20 V 0.73 V FF 84.56% 89.99% 69.27% η 20.0% 31.0% 11.0% SQ limit SRH limited *Nat. Energy 1, 15015 (2018)
17. CZTSe is CZTS with Higher J and Lower V 17 Se-poor Se-rich Zn-rich Cu-poor p0 ZnCu CuZn Sn Zn V Se V Se -Cu Zn VCu EF,p EF,n EF VCu CuZn VSe SnZn VS -CuZn Concentration (cm-3) Energy (eV) ZnCu VZn SQ limit SRH limited JSC (mA/cm2) VOC (V) SRH limited S-Q limit Best CZTSSe* JSC 48.25 mA/cm2 48.25 mA/cm2 35.2 mA/cm2 VOC 0.53 V 0.74 V 0.51 mV FF 79.81% 84.10% 69.8% η 20.7% 30.0% 12.6% *Adv. Energy Mater. 4, 1301465 (2013) Eg = 1.13 eV
18. CZGSe: Suppressed Inert-pair Effect New Hope or Different Challenges? - 5 0 5 10 0.0 0.5 1.0 1.5 2.0 Q (amu1/2 Å) Energy (eV) GeVI+e+h GeIII+h GeVI 18 Electron capture by GeZn 2+ Hole capture by GeZn 1+ Se-poor Se-rich Zn-rich Cu-poor Concentration (cm-3) Energy (eV) p0 VZn ZnCu Ge Zn VCu V Se -Cu Zn CuZn EF,p EF,n VCu CuZn VSe GeZn VSe -CuZn EF ZnCu V Se Configuration Coordinate of GeZn (2+/1+) SRH limited S-Q limit CZGSe* η 26.6% 32.2% 7.6% *Phys. Status Solidi (a) 215, 1800043 (2018)
19. Conclusion 19 Non-radiative Carrier Recombination Enhanced by Lone-pair Formation are not going to make us hate post-transition metal elements. We are going to understand them and love them. ACS Energy Lett. 3, 496 (2018) arXiv:1810.11259
20. Fate of Mankind Do not go gentle into that good night by Dylan Thomas Do not go gentle into that good night, Old age should burn and rave at close of day; Rage, rage against the dying of the light. Though wise men at their end know dark is right, Because their words had forked no lightning they Do not go gentle into that good night. … 20
21. Fate of Kesterite Do not go gentle into that good night Do not go gentle into that good night, Old age should burn and rave at close of day; Rage, rage against the non-radiative recombination. Though wise men at their end know dark is right, Because their words had forked no lightning they Do not go gentle into that good night. … 21