Achieving OPV Efficiency beyond 15%web.utk.edu/~opvwshop/files/Yang Yang-Gang Li.pdf · Outline •Review of OPV research status •Recent OPV results in UCLA –Single junction –Solution

Achieving OPV Efficiency beyond 15%

L. Dou, J. You, C-H. Chung, R. Zhu, Gang Li & Yang Yang

NSF/ONR Workshop on OPV – Arlington, VA - Sep. 20-21, 2012

Dept. of Materials Science and Engineering University of California Los Angeles

Email: [email protected] & [email protected]

Outline

• Review of OPV research status

• Recent OPV results in UCLA

– Single junction

– Solution process tandem OPV

• Perspective

– What do it take to get 15% OPV cell

– A proposal for 15% solution process solar cell

I. Status of OPV: Excitements & Challenges

• Fast progress since 08-09

• Double digit era now • Three entities have

Double digit OPV efficiency

• Polymer & small molecule

• Single junction & tandem cell

• Thermal evaporation & solution process

Mitsubishi Chemical – 10.1% PCE Small molecule / Solution process

Closest Published Info. – 5.2%

J. Am. Chem. Soc., 2009, 131 (44), 16048

Heliatek – 10.7% PCE Small molecule/ Vacuum process / Tandem

Closest Published Info. – 6.1%

Adv. Funct. Mater. 2011, 21, 3019

UCLA – 10.6% PCE Polymer / Solution process / Tandem

Closest Published Info. - 8.6%

a b

Nature Photon. 2012

7

II.A. Single Junction OPV Materials & Morphology control

Voc Jsc P3HT - BG:1.9 eV Silicon - BG 1.1 eV Solar cell Voc – 0.7 V OPV - too much energy loss

400 600 800 1000 12000

400

800

1200

1600

Irra

dia

nc

e [

Wm

-2m

-1]

P3HT:PCBM

cell response

AM 1.5G Reference

Spectrum (IEC 60904)

Wavelength [nm]

Silicon

SS

SS

SS

SS

SS

SS (100)

(200)

(300) (010)

qxy (Å-1)

0.0 0.5 1.0 1.5 2.0

SS

SS

SS

SS

SS

SS

a-axis

Substrate

200nm

G. Li, Y. Yang et al., NM (2005); Adv. Funct. Mater. (2007).

8

Examples – Co-polymer With Benzo [1,2-b:4,5-b′] dithiophene (BDT) unit

Mn: 27.4 kDa PDI: 1.8 Eg (Opt): 1.75 eV Voc = 0.92V / PCE = 5.7%

4,7-di-2-thienyl-2,1,3-benzothiadiazole

Thieno[3,4-b] thiophene

Yang Y. et al., Angew. Chem. Int. Ed. 49, 1500 (2010)

Y.Y. Liang et al. JACS. 131, 56 (2009)

400 600 800-10

0

10

20

30

40

50

60

70

EQ

E (

%)

Wavelength (nm)

PC61

BM

PC71

BM

D A

Voc Enhancement

LUMO

HOMO

LUMO

HOMO

Quinoid structure to lower bandgap

BDT unit to enhance planarity & mobility

PCE: 7 - 8% / IQE > 90% (2010)

9

II.B. Single Multi-junction Effective way for high efficiency

10

Single junction solar cell efficiency limit – 33% (J. Appl. Phys. 32, 510(1961))

Peter L M Phil. Trans. R. Soc. A

2011;369:1840-1856

Reducing thermalization loss!

R. King et al. Appl. Phys. Lett. 90, 183516 (2007 )

“40% efficient metamorphic GaInP/GaInAs/Ge

multijunction solar cells”

11

Courtesy of R. King, Spectralab

Tandem Polymer Solar Cells

- +

ITO

300 600 900 1200

0

1x1021

2x1021

3x1021

4x1021

5x1021

0.0

0.5

1.0

Ab

so

rban

ce (a

.u.)

Ph

oto

n D

en

sit

y (

Nu

mb

er

/m2/n

m)

Wavelength (nm)

Solar Spectrum

60% of

solar spectrum

Green polymer absorption

Red polymer absorption

PV1 PV2 n+ p+

hν

12

- + ITO

Regular

Inverted

• Two solar cells with complementary absorption range

• Reduce the “Quantum/Energy Loss” of high energy photons

• Transparent/conductive/robust interconnection layer (ICL)

• Multijunction solar cell compatible with Low-Cost Solution process

UCLA Tandem research – a Long way Traditional/Regular Tandem Cell

• Absorption range from 300nm to 850nm.

Glass / ITO Substrate

PEDOT:PSS

PSBTBT:PC70BM

P3HT:PC70BMPEDOT:PSS

h

PEDOT:PSSTiO2

Metal Electrode

TiO2:Cs

-+

PSBTBT P3HT

Glass / ITO Substrate

PEDOT:PSS

PSBTBT:PC70BM

P3HT:PC70BMPEDOT:PSS

hh

PEDOT:PSSTiO2

Metal Electrode

TiO2:Cs

-+

-+

PSBTBT P3HTPSBTBT P3HT

13 Sista, S. et al Adv. Mater. 2010, 22, 380–383

1.25V

0.66V 0.60V

PCE(%) Voc (V) Jsc (mA/cm2) FF(%)

P3HT:PC70BM 3.77 0.60 9.27 66.6

PSBTBT:PC70BM 3.94 0.67 10.71 55.8

Tandem 5.90 1.25 7.44 63.2

PBDTT-DPP based single junction cell

Low bandgap polymer (PBDTT-DPP, Eg=1. 44 eV)

High mobility (3.1×10-4cm2V-1s-1 )

Deep HOMO (-5.3 eV)

6.5 -7% power conversion efficiency (PCE) Nature Photonics, 6, 180 (2012)

Polymer / Solution process / Tandem

a

b

Dou et al. Nat. Photon. 2012

VOC (V) JSC

(mA/cm2)

FF (%) PCE

(%)

Front cell

(P3HT:ICBA)

0.85 9.56 70.2 5.7

Rear cell (PBDTT-

DPP:PC71BM)

0.74 13.5 65.1 6.5

Tandem (NREL) 1.56 8.26 66.8 8.6

State-of-art Polymer PV

Single Junction

Efficiency = 8.13%

9.31%

Tandem

Efficiency = 10.61%

III. Perspective on OPV going forward 1. Overcoming Jsc Deficit

17

10.6% polymer tandem OPV - ~60% IPCE

Science, 334, 629 (2011)

12.3% DSSC: 90+% IPCE

Approach: Light trapping Large EQE – IQE gap in OPV

Metal NP scattering @ interface

Excitation of localized surface plasmon

Excitation of surface plasmon polariton

Atwater et al. Nature Photonics (2011)

Approach 2: Interface Engineering

Hongbin Wu, Yong Cao et al. Nature Photonics (2012)

9.2% PCE & ~80% EQE

PTB-7 + PFN +

Inverted structure Glass

ITO ETL

Polymer blend

V2O5, MoO3, WO3

Electrode

Li, Yang et al. APL (2006)

Shrotriya, Yang et al., APL (2006)

Voltage loss in inorganic solar cell Typical: 0.4 – 0.5 eV, min: 0.32eV (GaAs)

R. King et al., Prog. Photovolt.: Res. Appl. 2011; 19:797

2. Overcoming Voc Deficit

Experimental: OPV Voc understanding & Status

Exciton dissociation Non-geminate

recombination

J. Nelson et al., JACS 134, 685 (2012)

Scharber, Brabec et al. Adv. Mater. 18, 789 (2006)

“Good” - EQE > 50 or 60%

Low bandgap

PBDTT-DPP:PCBM

BG = 1.44eV

Voc = 0.74V

Wide bandgap

(a) P3HT:ICBA

(b) PCDTBT:PBM

BG = 1.9eV

Voc = 0.85V / 0.90V

More work to do!

D. Veldmen et al., Adv. Funct. Mater.

19, 1939(2009)

Polymer Voc loss in OPV: >0.6 V

Brabec et al. Adv. Mater. (2009)

15% is NOT just a dream (Double-junction tandem scenario)

22

15% module ? @ $50/m2 $0.3/Wp @ $75/m2 $0.5/Wp

Simple math:

Same bandgaps & FF as in current 2-junct. OPV

EQE enhancement from 60% to 90% +

Bandgap – Voc offset of 0.7eV

20% double-junction OPV

3. Beyond Double Junction Tandem What’s the third junction? & Solution process!

A Fully solution-processed CIS solar cell

•Replacement of sputtered i-ZnO/ITO and better power conversion efficiency than control devices

24

0.0 0.2 0.4 0.60

-10

-20

-30 AgNW/ITO-NP

PCE=10.3%

Sputtered i-ZnO/ITO

PCE=9.35%

Bare AgNW

PCE=1.1%

Cu

rre

nt

de

nsity (

mA

/cm

2)

Voltage (V)

Mo

CuInSe2

CdS

ITO-NPAgNW

CdS

Mo

ITO-NP

AgNW

100 nm

CuInSe2

C.H. Chung, Y. Yang et al Adv. Mater. DOI: 10.1002/adma.201201010 (2012)

Voc(V) Jsc(mA/cm2) Efficiency(%) FF(%)

AgNWs- ITO NPs 0.494 30.11 10.31 69.34

i-ZnO/ITO 0.496 27.42 9.36 68.82

400 600 800 1000 1200

0

10

20

30

40

50

60

70

80

90

100

EQ

E (

%)

Wavelength (nm)

AgNWs-ITO NPs

Sputter i-ZnO/ITO1.9eV

1.4eV

I II III

Proposal: A Fully solution-processed Hybrid Triple Junction solar cell

Goal - High Efficiency & Low Cost

26

Organic photovoltaic technology Exciting progress Multiple reports on over 10% Challenges

Multi-junction approach is expected to lead us to 20% cell / 15% module Efficiency

Transparent OPV - an enabling / disruptive technology

Big Challenges & opportunities

Summary

Acknowledgement

27

• UCLA • Jing Gao •Dr. Ziruo Hong (U. Yamagata)

• Solarmer Energy Inc. • Dr. Yue Wu • Dr. Jianhui Hou (ICCAS) • Christine Tsai

• U. Chicago • Dr. Luping Yu • Dr. Yongye Liang (Stanford)

Acknowledgement

Thank you!