1

Magnetic Field Modulated Photovoltage

Ned Booker

Cavendish Laboratory

2

Origin of Photovoltage

J. Nelson, The Physics of Solar Cells (Imperial College Press, 2003)

Conduction Band

Valence band

Energy

Incident light

Ev

Ec

EFe

EFhVoc

Eg

𝑉 𝑜𝑐=𝐸𝑔+𝑘𝐵𝑇 ln( 𝑛𝑝𝑁 𝑝𝑁𝑣 )

3

Magnetic Field Effects

Intersystem Crossing(modulated by B field)

Particle Pairs

Free particles

Yield depends on pair spin

M. Cox, Technische Universiteit Eindhoven (2015)

4

Experimental Set-Up

Keithley 2400

sourcemeter

Magnet power supply

Device

Electromagnet Poles

White LED ring

Blue LEDLens

5

Variation of Magnetic Field

6

Photocurrent

A. Rao, et al., Nature 500, 435 (2013)

7

Photovoltage

𝑉 𝑜𝑐=𝐸𝑔+𝑘𝐵𝑇 ln( 𝑛𝑝𝑁 𝑝𝑁𝑣 )

8

Magneto-Photovoltage

9

Magneto-Photocurrent

10

Recombination Model

So

S1

A. Rao, et al., Nature 500, 435 (2013)

11

Recombination Model

So

S1

ISC

kdis,sing

CTT CTS

A. Rao, et al., Nature 500, 435 (2013)

12

Recombination Model

So

To

S1

CTT CTS

ISCFree charges

krec,trip

kdis,sing

kdis,CT

A. Rao, et al., Nature 500, 435 (2013)

13

Recombination Model

So

To

S1

CTT CTS

ISCFree charges

krec,trip

kdis,sing

kdis,CT

krec,bimol

A. Rao, et al., Nature 500, 435 (2013)

14

Transient Photovoltage

15

Fitted decay rates

16

Conclusion

• Magneto-photovoltage

• Magneto-photocurrent

• Transient Photovoltage

17

Outlook and Further Work

• Polymer:Fullerene ratio• Dope heavy metals• Perovskites (why not)• Quantum dots• Develop kinetic model• Any other suggestions…?

18

Thanks

• Professor Neil Greenham• Akshay Rao • Dan Credginton• Marc Etherington• Maxim Tabachnyk

19

Outlook and Further Work

20

Outlook and Further Work

M. Qian, et al., Advanced Materials 27, 3546 (2015).

21

Photovoltage with Blend Ratio

22

Different blend ratio devices

23

Repeatability and Artifacts

24

Reports of Magneto-Photocurrent

F.Wang, H. Bässler, Z. Valy Vardeny, Physical Review Letters 101, 236805 (2008).

25

Conclusion

26

Device Fabrication

PTB7-PCBM PIDTphanQ-PCBMPEDOT spin-speed (rpm) 4000 4000

Anneal Time (min), Temp (°C) 30, 150 30, 140

Polymer blend solvent DCB, DIO DCB

Active layer spin-speed (rpm) 2000 800 for 120 s, 2000 for 5 s

Anneal Time (min), Temp (°C) N/A 10, 110

Metal Contact (thickness (nm)) Ca (30), Al (100) Ca (30), Al (100)

27

Transient Photovoltage