Ad Advan vance ced d op optoe toelec lectronic tronic too - PowerPoint PPT Presentation

Ad Advan vance ced d op optoe toelec lectronic tronic too tools ls to in to inter terrogat rogate e sol soluti ution on-pr proces ocessed sola sed solar r ce cell lls Andrew M Telford Junior Research Fellow Imperial College London 1

Jenny Nelson’s group

New generation solar cells -+ - + sigmaaldrich.com greenoptimistic.com

The next step: biological electronics Credit: University of California, Berkeley ozbiosciences.com

Transients of the transient photovoltage spectroscopy (TrOTTr TPV) Dan Bryant (ICL, Chemistry) Xiaoe Li (ICL, Chemistry) Jenny Nelson (ICL, Physics) James Durrant (ICL, Chemistry) Matt Carnie (Swansea, Specific) Joel Troughton (Swansea, Specific) Brian O’Regan Phil Calado Piers Barnes

Hysteresis in perovskite solar cells 0.75 V o Current-Voltage scans exhibit hysteresis between forward and reverse scans o Short circuit current and open circuit voltage exhibits relaxation on the timescale of seconds CH 3 NH 3 PbI 3 (MAPI) 6

Ion migration C + - A a - + + n t - Cathode E ions Anode o h + d o - e d - + e E cell Voltage V oc Time Dark Light 7

Ion migration C + - A a - + + n t - E ions Cathode Anode o h + d o - e d - + e E cell Voltage V oc V precon < Voc Time Dark Light 8

Transients of the transient (TrOTTr) photovoltage measurements 9

The TrOTTr rig 10

TiO 2 bottom cathode architecture 0V 11

Ionic charge accumulation a) t = -60 s, Short Circuit b) t = -1 s, Short Circuit c) t = 0 s, Open Circuit d) t = 45 s, Open Circuit Cathode Cathode Cathode Cathode Anode Anode Anode Anode - + + + + - - - - + + - + - + - E field E E E Tress et al. EES 2015; Zhang Mater Horiz RSC 2015; 12 Xiao et al. Nat Mater. 2014; Eames et al. Nat. Comm. 2015

Hysteresis-free devices! • Changing contact materials appears to alter J-V hysteresis 13

Hysteresis depends on the contact materials Top cathode - ZnO Bottom cathode – TiO 2 Top cathode - PCBM ZnO 14

PCBM top cathode architecture 0V 15

The role of interfacial recombination o Without surface recombination, photogenerated charge carriers flood device and screen ionic charge Anode Cathode Anode Cathode HTL ETL ETL HTL E E 16

The role of interfacial recombination o With surface recombination, photo-carrier concentrations are low- ionic charge dominates E -field distribution Cathode Cathode Anode Anode HTL HTL ETL ETL E E 17 Van Reenen et al. JPCL 2015, DOI: 10.1021/acs.jpclett.5b01645

Jump-to-voltage photocurrent current transient E field No bias light  few background carriers Positive transient photocurrent observed in both architectures indicating reverse field 18

Conclusions • Mobile ions are present in the device regardless of hysteresis. • Surface recombination determines whether a reverse electric field at Voc is detectable or not. It also affects the extraction efficiency at 0<V<Voc. Recombination centres • Hysteresis can be reproduced in JV curves by switching ON or OFF the surface recombination, while allowing for ion migration. 19

Ho How D w Does oes the Ph the Photo oto-oxidation oxidation of of Ful Fuller lerenes enes Af Affe fect ct the the Beh Behav aviou iour r of of OP OPV D V Dev evic ices? es? Jason Röhr Beth Rice Alexandre Jenny Nelson De Castro Maciel Wing C. Tsoi (Swansea) James R. Durrant (Imperial, Chemistry) Zhe Li (Swansea) Jiaying Wu (Imperial, Chemistry Harrison K. H. Lee (Swansea) Emily Speller (Swansea)

Photo-oxidation of fullerene Degraded PCDTBT:PCBM PCDTBT:PCBM:O-PCBM 0 0 600 mins 2 ) 2 ) Current density (mA/cm Current density (mA/cm 3.6% -2 -2 1.8% 60 mins 0.9% 30 mins -4 -4 0.4% 10 mins 0.2% -6 -6 0 min, fresh 0%, Fresh Harrison K. H. -8 -8 Lee 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Voltage (V) Voltage (V) 6 Fresh 5 Ca/Al Degraded PCDTBT:PCBM PCDTBT:PCBM:O-PCBM 4 PCE (%) PCDTBT:PCBM 3 10 PEDOT:PSS 2 30 ITO 60 1 Glass 600 mins 0 0 1 2 3 4 5 21 Relative O-PCBM (%)

Photo-oxidation of PCBM O 2 PCBM PCDTBT N 2 PCDTBT:PCBM:O-PCBM PCBM 22

Photo-oxidation products Xiao et al. JACS 2007, DOI: 10.1021/ja0763798 Matsuo et al. Chem Comm 2012, DOI: 10.1039/c2cc30262d Epoxide Di-carbonyl LUMO HOMO Beth Rice 23

Mass spectrometry Fresh PCBM 100 910.1 (a) Relative Intensity (%) Mark F. Wyatt 0 850 900 950 1000 1050 1100 m/z 100 910.1 (b) Degraded 926.1 Relative Intensity (%) 958.1 PCBM in blend with PCDTBT 974.1 942.1 920 980 1040 926.1 958.1 974.1 0 m/z 850 900 950 1000 1050 1100 Degraded 100 910.1 (c) 926.1 PCBM in Relative Intensity (%) 958.1 solution 974.1 942.1 990.1 1006.1 1022.1 920 980 1040 926.1 958.1 974.1 990.1 0 850 900 950 1000 1050 1100 m/z 24

IR spectroscopy -1 1737 cm Photo-oxidation time 1.0 Normalised Absorbance 0min -1 1782 cm Emily Speller 10min 40min 100min 280min 610min 0.5 970min 1950min 0.0 1650 1700 1750 1800 1850 -1 ) Wavenumber (cm 25

Sub-band gap states in PCBM -3.6 eV -4.3 eV + -5.5 eV + -6.0 eV 26

Effect on RECOMBINATION #1: solar cell + -3.6 eV -4.3 eV + -5.5 eV -6.0 eV 27

What happens in the device? Charge Extraction Transient Photovoltage Intensity Pulse Intensity Bias ON Bias ON Light Bias OFF Light OC OC SC Voltage Voltage Cell Cell τ Δ n Δ N Δ Voltage Current Total Time [ μ s] Time [ns- μ s] 28

Charge extraction and Transient Photocurrent/Photovoltage Spectroscopies 0% O-PCBM 0% O-PCBM 0.4% O-PCBM 0.4% O-PCBM 1.4E17 1% O-PCBM 1% O-PCBM Charge carrier lifetime  [s] 1.2E17 Charge Density n [cm-3] 1E-4 1E17 8E16 6E16 1E-5 4E16 1E-6 2E16 16 17 17 0.70 0.75 0.80 0.85 0.90 5.0x10 1.0x10 1.5x10 -3 ] Voc [V] Charge carrier density n [cm CB CB CB Energy Energy Energy V oc V oc V oc Jiaying Wu Ln DoS Ln DoS Ln DoS 29

Voc reconstruction 0% measured 1.0 0% reconstructed 0.4% measured 0.4% reconstructed 1% measured 1% reconstructed Voc (V) 0.8 1 2 3 4 5 light intensity (sun equivalents) 30

Effect on RECOMBINATION #2: LED -3.6 eV + -4.3 eV -5.5 eV + -6.0 eV 31

Electroluminescence O-PCBM 1 0% 0.2% Normalised EL 0.4% 0.9% 1.8% 3.6% 0 1.0 1.2 1.4 Energy [eV] 32

EL of pure blend components Red-shift or change in oscillator strengths? PCBM fresh 1.0 Ca/Al PCBM degraded PCBM Normalised EL 0.5 PEDOT:PSS ITO Glass 0.0 1.0 1.2 1.4 1.6 1.8 Energy [eV] Fresh PCDTBT Ca/Al 1.0 Degraded PCDTBT 0.8 PCDTBT Normalised EL 0.6 PEDOT:PSS 0.4 ITO 0.2 Glass 0.0 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 33 Energy [eV]

Electroluminescence and external quantum efficiency 1 0.1 1E-3 1 1E-3 Normalised EL 1E-5 1E-5 Normalised EL EQE 1E-7 1E-7 0.1 EQE 0.1 O-PCBM 1E-9 0% 1E-9 0.2% 1E-11 1E-11 0.4% 0.9% 0.01 1E-13 E g 1E-13 1.8% 1.0 1.5 Energy [eV] 3.6% 0.01 1E-15 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Energy [eV] ∞ 𝑃𝐷,𝑠𝑏𝑒 = 𝑙𝑈 𝑟 𝑚𝑜 𝐾 𝑡𝑑,𝑠𝑏𝑒 𝑊 + 1 𝐾 0,𝑠𝑏𝑒 = 𝑟 න 𝐹𝑅𝐹 ∙ 𝜚 𝑐𝑐 𝑒𝐹 𝐾 0,𝑠𝑏𝑒 0 34

Open-circuit voltage losses 2.0 Eg/q Voc non-rad. loss abs. loss SQ loss SQ limit 1.5 EL-QE Voltage [V] 1.0 Solar Simulator 0.5 0.0 0% 0.2% 0.4% 0.9% 1.8% 3.6% O-PCBM content 35

Conclusions HOMO-LUMO Transport simulations TRAPS! Voltage losses from Recombination at non-radiative the D/A interface recombination 36

Thanks • • Piers Barnes (Imperial) Wing C. Tsoi (Swansea) • • James Durrant (Imperial) Zhe Li (Swansea) • • Dan Bryant (Imperial) Matt Carnie (Swansea) • • Xiaoe Li (Imperial) Joel Troughton (Swansea) • • Xuhua Wang (Imperial) Josep Sancho (Valencia) • • Saif Haque (Imperial) Brian Saunders (Manchester) • • Paul O’Brien (Manchester) Irene Sanchez (Imperial) • • Emily Speller (Swansea) Paul McNaughter (Manchester) • • Brian O’Regan ( Sunlight Harrison K. H. Lee (Swansea) Scientific) • Emily Speller (Swansea)