Charge Carrier Recombination Dynamics in Perovskite and Polymer

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Keywords: Perovskite Photovoltaics; Organic Photovoltaics; Recombination; .... neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (EKSPLA NT 242).
Supporting Information

Charge Carrier Recombination Dynamics in Perovskite and Polymer Solar Cells Andreas Paulke1, Samuel D. Stranks2, 3, 4, Juliane Kniepert1, Jona Kurpiers1, Christian M. Wolff1, Natalie Schön1, Henry J. Snaith2, Thomas J.K. Brenner1 and Dieter Neher1* Keywords: Perovskite Photovoltaics; Organic Photovoltaics; Recombination; Charge Extraction;

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Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str.24-25, 14476 Potsdam-Golm, Germany 2 Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom 3 Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States 4

Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom

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1. Review on published recombination coefficients S1: Review of published charge carrier recombination coefficients for the perovskite CH3NH3PbI3-xClx. Sample type

Pero

Method

Fluence

Deposition

Analysis

NT

k1 -3

Range

[cm ]

[µJ/cm²]

k3

Ref

[1/s]

3

[cm /s]

[cm /s]

6

4.9E6

8.7E-11

9.9E-29

1

Traps

Quartz/

1 step

MAI:PbCl2 (3:1)

Optical Pump

6

1st, 2nd,3rd

Meso-Al2O3/Pero

solution

CH3NH3PbI3-xClx

(550nm)

- 320

order

PL not important

(devices ECE = 12.7%)

-Thz Probe

+ account for

for good fits

500nm infiltrated

k2

-

Inhom. excitation n(z) MAI:PbI2 (3:1)

-

15E6

9.4E-10

3.7E-29

1

-

14E6

9.2E-10

1.3E-28

1

12E6

1.1E-10

2.3E-29

2

< 0.5E15

~kT*NT (e-)

4.9E-10

-

3

60E15

--

3.5E-10

-

CH3NH3PbI3 (ECE = 8.5%) MAI:PbI2 (1:1) CH3NH3PbI3 (ECE = 0.9%) Quartz/Pero(330nm)

evaporation

MAI:PbCl2 (4:1)

Optical Pump

6

CH3NH3PbI3-xClx

(550nm)

- 188

-Thz Probe Quartz/Pero

1 step solution

MAI:PbCl2 (3:1)

Optical Pump

3E-4

MAI:PbI2 (1:1)

(600nm) TRMC

-3

BMR + trapping

Quartz/MesoAl2O3/

MAI:PbCl2 (3:1)

7E15

--

7E-10

-

Pero 400nm infiltrated

MAI:PbI2 (1:1)

6E15

--

6E-10

-

kSHR

kSurf

0.42E6(9%)

7.7E6(91%)

2.5E-10

2.8E-27

FTO/Pero(200 nm)

2step

CH3NH3PbI3

All Optical TAS

1st, 2nd,3rd

2

2

3

4

(MAI dip)

FTO/mp-TiO2/

2step

Pero(350nm)/Spiro

(MAI dip)

Glass/mp-Al2O3:Pero

1 step

– 70

CH3NH3PbI3

2–

0.42E6 (42%)

2.2E6(58)

10E-10

2E-27

4

70 CH3NH3PbI3 (1:1)

All Optical TAS

(600 nm)

Glass/Pero(280nm)

order

1–

BMR

5

2.3E-9

40

2step

CH3NH3PbI3

(MAI dip) ?

CH3NH3PbI3-xClx

TR-PL

0.02 –

BMR +

(688nm Exc)

0.5

trapping

TR-PL

?

BMR +

(510 nm

1.8E7

1.7E-10

--

6

7

1.3E-10

trapping

Excitation) Quartz/MesoAl2O3/

1step

CH3NH3PbI3

TRMC

CH3NH3PbI3 (1:1)

TRPL

BMR

13E-10

--

8

2.6E-10

3E-28

9

Pero

CH3NH3PbI3-xClx (3:1)

Quartz -/MesoAl2O3/ Pero

TRMC 1step

0.05 –

k2 ~ 1/n

500

Son non-BMR?

- Meso-TiO2/Pero - Pero

3

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2. Summary of TDCF results & jV characteristics S2: Summary of the device parameters and recombination coefficients obtained by the TDCF experiments PTB7:PCBM

Planar

Perovskite



organic

interlayers Observed

Strictly bimolecular +

Recombination mechanism

contributions from

Bimolecular + slowdown of rate

background charges 9

9.2

Vpre [V]

0.7

0.7

Voc [V]

0.72

0.91

Active Layer Thickness

100

300

1

1

min

0.5

0.2

max

1.5

0.8

min

0.2

0.1

max

0.6

1

500

532

PCE (AM 1.5G) [%]

[nm] Pixel Size [mm²] Qtot [10-9C] initial

Fluence [µJ/cm²]

Excitation Wavelength [nm] Average initial

min

3

0.4

Carrier Density

max

9

1.6

1.6 x 10-11

1 x 10-9

16

-3

[10 cm ] BMR-coefficient -1

[cm³s ] Background charge

time dependence 0.22

-9

(no obvious influence seen)

[10 As]

Explanation

0.1

Homogeneous carrier

Inhomogeneous carrier distribution,

distribution, free carrier

trapping + surface recombination?

recombination

.

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S3:Current density vs. voltage under 100 mWcm-2 AM 1.5G illumination of the devices. For the planar perovsktie device the forward and backward scan taken with a scan rate of 125 mV/s are shown.

S4: Short Circuit current density vs illumination intensity of the planar perovskite device. The intensity was varied by putting optical density filters in front of the AM 1.5G solar simulator. The short ciruit current density shows a slight sub-linear dependence on the illumination intensity.

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3. Experimental Details 3.1 Device Preparation Organic solar cells: Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (Heraeus Clevios Al 4083) was spin coated onto cleaned and plasma etched indium tin oxide (ITO) glass at 2400 r.p.m. for 30 seconds and annealed in air at 120°C for 10 minutes. A blend of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl})

(PTB7) (1-

material) and PC70BM (Solenne) were separately dissolved in chlorobenzene (CB), then mixed to a 1:1.5 (by weight) solution with a concentration of 25 mgmL-1 and subsequently spin coated at 1000 r.p.m. This resulted in an active layer thickness of around 100 nm. Finally, 5 nm Ca and 80 nm Al were thermally evaporated through shadow masks, defining an active area of 1 to 16 mm2. Small pixels were used to avoid RC-time limitations in the transient measurements. The device was finally encapsulated with epoxy resin and a glass lid prior to air exposure.

Planar perovskite solar cells: Onto ITO/PEDOT:PSS substrates prepared in identical fashion to those used for organic solar cells, the perovskite was deposited in a two-step spin coating procedure. First lead iodide (PbI2, Sigma Aldrich, 99.9999%) was dissolved in DMF with a concentration of 460 mgmL -1. Methylammonium iodide (Dyenamo) was separately dissolved in isopropanol with a concentration of 42 mgmL-1. Then PbI2 was spin coated at 4000 r.p.m. for 35 s followed by 2000 r.p.m. for 3 s. Afterwards the film was annealed for 10 minutes at 70 °C inside the glove box. Subsequently the MAI solution was spun at 4000 r.p.m. for 35 s and annealed outside the glove box for 1 hour at 100 °C. Afterwards, a thin layer of PC60BM (Solenne) in dichlorobenzene (4000 r.p.m. for 35 s) was spin-coated on top of the perovskite, followed by a 100°C drying step for 30 minutes inside the glove box. Finally, 7 nm of C60 (MER Corporation) and 20 nm of bathocuproine (BCP) (Sigma-Aldrich) were evaporated with a rate of 0.1 Å/s and completed by a 100 nm thick aluminium electrode (pressure < 2x10-6 mbar). All samples were encapsulated with epoxy resin and a glass lid prior to air exposure. All materials were used as received.

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3.2 Methods J-V characteristics of the solar cells were measured with an Oriel class A simulator calibrated to 100 mW cm-2 and a Keithley 2400 sourcemeter under inert atmosphere. In the TDCF experiments, pulsed excitation (5.5 ns pulse width, 500 Hz repetition rate) was realized with a diode-pumped, Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (EKSPLA NT 242). The photogenerated charge carriers were extracted by applying a high rectangular voltage pulse with a pulse generator (Agilent 81150A) in reverse direction. The current through the device was measured with an Agilent DSO9054H oscilloscope via a 50 Ω input resistor. A detailed description can be found in our previous work11. Layer thicknesses were determined with a Dektak 3ST profilometer.

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4. Comparison of Recombination Dynamics

S5: Comparison of the recombination dynamics for the devices investigated in this study, highlighting the fundamentally different time scales.

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5. Initial Carrier Density vs. Fluence

S6: Comparison of initial (Delay = 10 ns) fluence-dependent photogenerated carrier densities for the different devices, highlighting the fast initial recombination process for the planar perovskite device (left panel). The calculated external generation efficiency (EGE) decreases for the planar perovskite device already at rather low excitation densities (right panel).

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6. Static and time-resolved PL of the planar Perovskite/PCBM

S7: Steady state photoluminescence (Excitation at 532 nm) measured for the planar perovskite film on glass with a PCBM layer coated on top with varying PCBM concentrations.

S8: Time-resolved photoluminescence (Excitation at 532 nm) measured for the same layers as in Figure S3. The PL traces are labelled with their corresponding 1/e time constants.

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7. SEM & AFM images of the planar perovskite film

S9:SEM image of the planar perovskite film showing grain sizes of ~200 nm.

S10:AFM images of the planar perovskite film showing grain sizes of ~200 nm and a height variation of ~50nm.

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8. TDCF on the planar perovskite device with varying prebias

S11: TDCF measurements on the planar perovskite device with varying prebias.

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References 1.

Wehrenfennig, C., Eperon, G. E., Johnston, M. B., Snaith, H. J. & Herz, L. M. High charge carrier mobilities and lifetimes in organolead trihalide perovskites. Adv. Mater. 26, 1584–1589 (2014).

2.

Wehrenfennig, C., Liu, M., Snaith, H. J., Johnston, M. B. & Herz, L. M. Charge-Carrier Dynamics in VapourDeposited Films of the Organolead Halide Perovskite CH3NH3PbI3− xClx. Energy Environ. Sci. 7, 2269 (2014).

3.

Hutter, E. M., Eperon, G. E., Stranks, S. D. & Savenije, T. J. Charge Carriers in Planar and Meso-Structured Organic–Inorganic Perovskites: Mobilities, Lifetimes, and Concentrations of Trap States. J. Phys. Chem. Lett. 6, 3082–3090 (2015).

4.

Piatkowski, P. et al. Direct Monitoring of Ultrafast Electron and Hole Dynamics in Perovskite Solar Cells. Phys. Chem. Chem. Phys. (2015). doi:10.1039/C5CP01119A

5.

Manser, J. S. & Kamat, P. V. Band filling with free charge carriers in organometal halide perovskites. Nat. Photonics 8, 737–743 (2014).

6.

Yamada, Y., Nakamura, T., Endo, M., Wakamiya, A. & Kanemitsu, Y. Photocarrier Recombination Dynamics in Perovskite CH3NH3PbI3 for Solar Cell Applications. J. Am. Chem. Soc. 136, 11610–3 (2014).

7.

Stranks, S. D. et al. Recombination Kinetics in Organic-Inorganic Perovskites: Excitons, Free Charge, and Subgap States. Phys. Rev. Appl. 034007, 1–8 (2014).

8.

Savenije, T. J. et al. Thermally activated exciton dissociation and recombination control the carrier dynamics in organometal halide perovskite. J. Phys. Chem. Lett. 5, 2189–2194 (2014).

9.

Saba, M. et al. Correlated electron–hole plasma in organometal perovskites. Nat. Commun. 5, 5049 (2014).

10.

Oga, H., Saeki, A., Ogomi, Y., Hayase, S. & Seki, S. Improved understanding of the electronic and energetic landscapes of perovskite solar cells: high local charge carrier mobility, reduced recombination, and extremely shallow traps. J. Am. Chem. Soc. 136, 13818–25 (2014).

11.

Kniepert, J. et al. The Effect of Solvent Additive on Generation, Recombination and Extraction in PTB7:PCBM Solar Cells: A Conclusive Experimental and Numerical Simulation Study. J. Phys. Chem. C 119, 8310–8320 (2015).

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