Cells Sunghyun Kim, Ji-Sang Park, Samantha N. Hoods and Aron Walsh Dept. of Materials, Imperial College London, UK firstname.lastname@example.org | frssp.github.io | frssp | 0000-0001-5072-6801 2018 – EU Kesterite Workshop ACS Energy Lett. 3, 496 (2018) arXiv:1810.11259
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.
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.
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
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)
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
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)
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)
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
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