Voc impact of orientation-dependent x in anisotropic PV absorbers.

Transcription

1 Voc impact of orientation-dependent x in anisotropic PV absorbers The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Chakraborty, Rupak,David Berney Needleman, Kelsey Doolittle, Naiall M. Mangan, Vera Steinmann, Jeremy R. Poindexter, Alex Polizzotti, Chuanxi Yang, Roy G. Gordon, Tonio Buonassisi Voc impact of orientation-dependent x in anisotropic PV absorbers. Materials Research Society Fall Meeting, Boston, Massachusetts, November 29 - December 4, Citable link Terms of Use This article was downloaded from Harvard University s DASH repository, and is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at nrs.harvard.edu/urn-3:hul.instrepos:dash.current.terms-ofuse#oap

2 V OC impact of orientation-dependent χ in anisotropic PV absorbers Rupak Chakraborty 1 David Berney Needleman 1, Kelsey Doolittle 1, Niall M. Mangan 1, Vera Steinmann 1, Jeremy R. Poindexter 1, Alex Polizzotti 1, Chuanxi Yang 2, Roy G. Gordon 2, and Tonio Buonassisi 1 1 Massachusetts Institute of Technology 2 Harvard University Fall MRS 2015 Symposium NN December 3, 2015

3 V OC deficit in SnS Many PV material systems are plagued by low V OC CZTS, WS 2, FeS 2, SnS V deficit OC = E g q V OC = 728 mv What causes low V OC? P. Sinsermsuksakul et al., Adv. Energy Mater. 4, (2014). 1

4 Band fluctuations: constant χ V deficit OC significantly influenced by electrostatic potential fluctuations 1,2 χ constant E vac E E g constant E c E v ~10 mev position 1,2 J.H. Werner et al., Thin Solid Films , 399 (2005). 1,2 Gokmen et al., Applied Physics Letters 103 (2013) 2

5 Band fluctuations: variable χ E vac χ variable E E g constant E c E v ~100 mev position 3

6 Max measured Δχ (ev) Surface orientation-dependence of electron affinity χ 110 χ 111 χ 100 Δχ = χ hkl χ h k l (Calculated) 0.9 ev! Si 1 CuGaSe 2 2 GaAs 3 In 2 O 3 4 SnS 5 Wulff construction: Zucker et al., Journal of Materials Science 47: (2012). 1 J.W. Keister et al., J. Vac. Sci. Technol. B 17, 1831 (1999). 2 S. Sadewasser et al., Appl. Phys. Lett. 80, 2979 (2002). 3 W. Ranke, Phys. Rev. B 27, 7807 (1983). 4 M. Hohmann et al., J. Phys. Condens. Matter 23, (2011). 5 V. Stevanović et al., Appl. Phys. Lett. 104, (2014). 4

7 Lateral CBO variation due to grain orientation (hkl) (h k l ) buffer absorber back contact What is the impact of orientation-dependent electron affinity Cliff offset on SnS device Spike performance? offset E c E c E v E F E v E F absorber buffer 5

8 Simple test case: two-grain model Top contact ZnO Zn(O,S) Top contact ZnO Zn(O,S) χ 1 χ 2 SnS grain 1 SnS grain 2 Back contact Back contact Single stack previously modeled in SCAPS 1D 1 1 Mangan et al., J. Appl. Phys. 118, (2015). 6

9 χ 2 (ev) Electron affinity parameter space χ 1 (ev) 7

10 χ 2 (ev) Efficiency impact η (%) Optimal η χ 1 (ev) 8

11 χ 2 (ev) V OC impact V OC (V) Cliff offset Optimal η Cliff offset χ 1 (ev) 9

12 χ 2 (ev) J SC impact J SC (ma/cm 2 ) Spike offset Optimal η Spike offset χ 1 (ev) 10

13 χ 2 (ev) Efficiency impact η (%) Current blocking Optimal η Current blocking 1.1% absolute 22% relative loss χ 1 (ev) 11

14 Summary Abrupt lateral fluctuations in χ are expected in SnS due to orientation dependence Current blocking is worst effect Avoided by optimizing buffer layer V OC still reduced because of cliff offset 22% relative loss in efficiency for Δχ = 0.9 ev 12

15 Further work Confirm χ(hkl) in SnS experimentally >2 grains in parallel Top contact ZnO Zn(O,S) χ 1 Top contact ZnO Zn(O,S) χ 2 Top contact ZnO Zn(O,S) χ 3 SnS grain 1 SnS grain 2 SnS grain 3 Back contact Back contact Back contact 13

16 Further work Confirm χ(hkl) in SnS experimentally >2 grains in parallel Simulation accounting for 2D carrier flow Top contact ZnO Zn(O,S) χ 1 χ 2 SnS grain 1 SnS grain 2 Back contact 14

17 Acknowledgments PVLab at MIT Gordon Group at Harvard Harvard Center for Nanoscale Systems Center for Materials Science and Engineering at MIT U.S. Dept. of Energy Grant (DE-EE ) 15

18 χ 2 (ev) Thank you! η (%) Current blocking Optimal η Current blocking 1.1% absolute 22% relative loss χ 1 (ev) 16