Metal-halide perovskites: the next evolution in photovoltaics

Transcription

1 Metal-halide perovskites: the next evolution in photovoltaics D r. C o l i n B a i l i e Po stdoc, Sta n fo rd U n i ve rs i t y Fo u n d e r, I r i s P V * D a t a i n t h i s p r e s e n t a t i o n f r o m t h e l a b a t S t a n f o r d * Global Climate and Energy Project

2 2 Fastest-improving PV technology in history

3 Perovskite describes a crystal structure class Generic formula: ABX 3 A B X CH 3 NH 3 + Pb 2+ I - CH 3 NH 3 PbI 3 Methylammonium-lead-iodide 3

4 Perovskite solar cells have versatility in their architecture Energy diagram: 4

5 Perovskite processing is simple and fast 5 VIDEO CREDIT: JOEL TROUGHTON, YOUTUBE

6 6 The perovskite is a strongly-absorbing direct band gap semiconductor

7 The perovskite is already an efficient solar cell technology Material Bandgap (ev) q Voc (ev) Energy loss (ev) GaAs Perovskite (MAPbBr 3 ) 0.15 (FaPbI3) Silicon CIGS ~ CdTe a-silicon M. GREEN ET AL. SOLAR CELL EFFICIENCY TABLES (VERSION 46) 2015 J. P. C. BAENA, A. HAGFELDT, ET AL., ENERGY & ENVIRON. SCI W. S. YANG, S. I. SEOK, ET AL., SCIENCE 2015

8 Time resolved photoluminescence (TRPL): Carrier Carrier lifetime can be long τ= 261ns τ= 4ns 8

9 Defects in perovskites are shallow Yanfa Yan et al. Adv. Materials,

10 Tuning the composition adjusts the band gap CH 3 NH 3 PbI 3 E g =1.6 ev CH 3 NH 3 PbBr 3 (MA)Pb(Br x I 1-x ) 3 E g =2.3 ev CH(NH 2 ) 2 PbI 3 E g =1.48 ev CH(NH 2 ) 2 PbBr 3 CH(NH 2 ) 2 Pb(Br x I 1-x ) 3 E g =2.2 ev Snaith et al. Energy Environ. Sci., 7, (2014) 10

11 Advantages of perovskites Tunable band gap Highly absorbing Long carrier lifetimes (slow bulk recombination) Low surface recombination (slow surface recombination) They can be printed, even on plastic! 11

12 Use double junction tandems to reach >30% efficiency Single-Junction Theoretical Efficiency Double-Junction Theoretical Efficiency SHOCKLEY AND QUEISSER (1961), DE VOS (1980). NOTE: INPUT SPECTRUM IS 6000 K BLACKBODY; STANDARD AM1.5G SOLAR SPECTRUM YIELDS SLIGHTLY DIFFERENT VALUES. 12

13 Tandems overcome single-junction efficiency limits Silicon practical efficiency limit: 25% Perovskite/silicon tandem practical efficiency limit: 30-35% 13

14 Perovskite bandgap is tunable over the ideal range for the top cell in a tandem CH 3 NH 3 PbI 3 [E g =1.6 ev] CH 3 NH 3 PbBr 3 [E g =2.3 ev] DE VOS. J. PHYS. D: APPL PHYS (1980) CH 3 NH 3 Pb(Br x I 1-x ) 3 14

15 Two potential scalable tandem architectures mechanically stacked monolithically integrated COLIN D. BAILIE, MICHAEL D. MCGEHEE, MRS BULLETIN (2015) 15

16 Mechanically-stacked tandem on silicon using ITO as the rear electrode Separate Tandem 12.3% 12.3% % 5.7% mechanically stacked 18.0% K. A. Bush, C. D. Bailie, Y. Chen, T. Leijtens, A. R. Bowring, F. Moghadam, M. D. McGehee, Adv. Materials (2016) Silicon image from Yu et al. J. Micro/Nanolith. MEMS MOEMs (2009) 16

17 2-terminals coming out of the junction box of a mechanically-stacked tandem Flexibility to match voltage or current of the top and bottom strings C.D. BAILIE, M. G. CHRISTOFORO, J.P. MAILOA, M. D. MCGEHEE, ET AL., ENERGY ENVIRON. SCI., 2015,

18 Current World Record Mechanically Stacked Perovskite on Si Tandem J. Werner, C. Ballif et al, ACS Energy Letters 1 (2016) p

19 First Monolithic Perovskite/Silicon Tandem 13.7% with 11.5mA/cm 2 Significant parasitic absorption in the hole transport material Spiro-OMeTAD Mailoa, J. P. and Bailie, C. D., et al. (2015). Applied Physics Letters, 106,

20 20 Bandgap tuning with alloyed materials MA Pb I, Br Top cell E g range Can change the bandgap by controlling the halide composition Bandgap can be tuned from ev for CH 3 NH 3 Pb(Br x I 1-x ) 3 20 Hoke, E. T. et al. Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics. Chem. Sci. 6, (2014).

21 21 Phase segregation in mixed halides limits the V oc x=0.4 Arrows show increasing time Phase segregation for all CH 3 NH 3 Pb(Br x I 1-x ) 3 with x> Hoke, E. T. et al. Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics. Chem. Sci. 6, (2014).

22 PL spectra very similar over composition range of (MA)Pb(Br x I 1-x ) 3 after light soaking PL (arb.units) Wavelength (nm) Energy (ev) x=0 x=0.1 x=0.2 x=0.3 x=0.4 x=0.5 x=0.6 x=0.7 x=0.8 x=0.9 x=1 Mixed halide PL spectra similar to what would be expected for (MA)Pb(Br 0.15 I 0.85 ) 3, (x~0.15) 22

23 Selecting the high band gap semiconductor Eg Material(s) Device efficiency 1.5eV FAPbI % (FAPbI 3 ) 0.85 (MAPbBr 3 ) % 1.6eV MAPbI 3 FA 0.9 Cs 0.1 PbI 3 Triple cation* 19.7% 16.5% 21.1% 1.7eV FA 0.83 Cs 0.17 (I 0.6 Br 0.4 ) 3 MAPbBr 0.8 I % 14.9% Stable to phase segregation Yes? Yes Yes? Possibly No Group Seok Seok Park Grätzel Grätzel Snaith Huang 1.8eV MAPbBr 0.9 I % No Zou 1.9eV CsPbBrI 2 6.5% Yes McGehee Snaith 2.3eV MAPbBr 3 8.7% CsPbBr 3 6.5% Yes Yes Green Cahen 23 *Triple cation formula: Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3

24 Current Density (ma/cm2) Our best monolithic 2-terminal tandem Cs 0.17 FA 0.83 Pb(Br 0.17 I 0.83 ) 3 perovskite on heterojunction silicon from Zach Holman s team at ASU 1cm % efficient very stable Voltage (V) 24

25 EQE and 1-R (%) Perovskite/HIT Tandem EQE and 1-R Wavelength (nm) EQE Sum IR HIT2 - Perovskite EQE mA IR HIT2 - Silicon EQE mA IR HIT 2-1-R 25

26 Main limitation for perovskite is demonstration of 25- year field lifetime Light breaks bonds Halides corrode metals Heat vaporizes organics Water reacts chemically 26 Review Article: Tomas Leijtens et al. Stability of Metal Halide Perovskite Solar Cells, Advanced Energy Materials, 2015.

27 Several studies demonstrate that non-metal electrodes work better than metal ones Carbon electrodes enable stable devices Mei, A. et al. A hole-conductor free, fully printable mesoscopic perovskite solar cell with high stability. Sci. 345, (2014). EPFL: gold diffuses in solar cells Domanski, K. et al. Not all that glitters is gold: metal-migrationinduced degradation in perovskite solar cells. ACS Nano 10, (2016). Halogens react with metal Back, H. et al. Achieving long-term stable perovskite solar cells via ion neutralization. Energy Environ. Sci. 9, (2016). 27

28 Stability remains a major barrier to perovskite solar cells K. A. BUSH, C. D. BAILIE, Y. CHEN, T. LEIJTENS, A. R. BOWRING, F. MOGHADAM, M. D. MCGEHEE, ADV. MATERIALS (SUBMITTED) 28

29 29 Aluminum Doped Zinc Oxide (AZO) Enables Sputtering of ITO as the Top Electrode Hole blocking layer Sputtering buffer layer -3.9eV ITO -4.2eV -4.4eV -4.8eV Al:ZnO nps PC 60 BM ITO MAPbI 3 ITO -4.8eV PEDOT PC 60 BM Perovskite -5.2eV -5.4eV -6.0eV ZnO PEDOT:PSS ITO Glass -7.6eV 29

30 30 Progress in Sputtering ITO as the Top Electrode MgF 2 (150nm) ITO (500nm) Al:ZnO nps (50nm) PC 60 BM (40nm) Perovskite (~275nm) 200nm PEDOT:PSS (40nm) ITO (150nm) Glass Sunpreme Ye Chen, Wei Wang, Wen Ma, Farhad Moghadam 30

31 Improved thermal and environmental stability with sputtered ITO electrode 31 K.A. Bush, C.Bailie, M. McGehee et al., Adv. Mat, 28 (2016) 3937.

32 ITO-sealed perovskite on hot plate at 150 C K. A. BUSH, C. D. BAILIE, Y. CHEN, T. LEIJTENS, A. R. BOWRING, F. MOGHADAM, M. D. MCGEHEE, ADV. MATERIALS (SUBMITTED) 32

33 Packaging devices Solar glass (3.2mm, Pilkington) Edge seal (Butyl, Quanex) Bus bars (Cu + Sn/Ag/Cu coating, Ulbrich) Conductive adhesive (Sn/Bi, Hitachi) Encapsulants (EVA, PO) Encapsulant (Surlyn) Side View Top View Encapsulant Bus Bars Edge Seal Space-filling glass Perovskite Solar Glass 33

34 Testing of Fully Encapsulated Devices in 85 C/85% RH Damp Heat 6 weeks = 1000 hours 34

35 Fracture Energy, G c (J/m 2 ) Fracture Properties of Device Materials 1, Polymers for Packaging Encapsulation Protective Coatings Dense SiO 2 TEOS SiO 2 ULK dielectrics Structural Materials Silicon PV Al doped ZnO CdS CuIn x Ga (1-x) Se 2 Mo Al foil CIGS OPV Ag P3HT CH 3 NH 3 PbI 3 ZnO ITO-PET G c ~ 10 J/m 2 G c ~ 5 J/m Perovskites

36 Outlook on stability Using the more stable perovskites, impermeable and unreactive electrodes and proper packaging has improved stability enormously. We have passed a temperature cycling test and the damp heat test. Long-term testing under light is underway hour tests are encouraging. 36

37 Outlook Single junction efficiencies approaching 25 % seem possible. Band gaps for single and multijunction tandems are available. Breaking 25 % efficiency with tandems is inevitable and 30 % look achievable. Stability is rapidly improving. 37

38 What are the implications of Pb being toxic? Babayigit et al. Nature Materials, 15 (2016)

39 Amount of lead The panels will have about 1 g of lead in the perovskite. Silicon panels typically have 16 g of lead in the solder. Lead would not easily escape a packaged module. 39

40 Perovskite companies Company Location Approach Oxford PV England Perovskite on Si monolithic 2T tandem Iris PV Silicon Valley Perovskite mechanically stacked on Si Tandem Hunt Energy Dallas, Texas Single junction perovskites Saule Poland Flexible perovskite cells Weihua Solar China Printed single junction panels 40

41 41 Acknowledgments Michael McGehee Rachel Beal, Kevin Bush, Andrea Bowring, Rongrong Cheacharoen, Eric Hoke, Tomas Lietjens, Axel Palmstrom, Dan Slotcavage Duncan Hargrave at D2 solar Homer Antoniadis at DuPont Jonathan Mailoa, Robert Hoye, Tomas Leijtens, Sarah Sofia, Tonio Buonassisi at MIT Zhengshan J. Yu, Mathieu Boccard, Zach Holman at ASU Ye Chen, Wei Wang, Wen Ma, Farhad Moghadam at Sunpreme 41