YY LABs

UCLA

High performance organic and hybrid solar cells

Department of Materials Science and Engineering

University of California, Los Angeles

Gang Li, Yang Yang

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YY LABs

UCLA

Research - Pursuing “Game-change” PV technology

• Low-cost: materials, processing, and …

• High Performance: to lower the energy cost.

• Easy installation.

• UCLA PV research - Solution process thin solar cell technology: organic, inorganic and hybrid approaches.

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YY LABs

UCLA

Si Solar Cell

The King (~90% market) now

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Can we do better – Printing? –

Solution Process?

YY LABs

UCLA

Thin Film PV Research at UCLA

2013

Perovskite

2014, 17-19%**

PVSK (planar

structure)

Hybrid

2007 CIGS

2011 CZTS

2013 8.5% CZTS

2011 11% CISS

Inorganic

* Certified ** Un-certified

2001 OPV

2013 10.6% Tandem*

2013 10.2% SM

Tandem OPV* 2012 8.6% Tandem*

2010 First Tandem Device

2006 First Inverted Device

2005 4% Morphology

Control*

Organic

2014 11.5% Triple Junction

YY LABs

UCLA

Bulk Heterojunction Polymer Solar Cells

S SS S

n/4

O

OCH2

P3HT PCBM

e-

Invented in California/UC

Developed in California/UC

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UCLA

Why Organics: Unlimited Possibilities Out of C, H, O … - Tunability

S

S

O

S

S

S

S

n

S

Si

S

S

NO O

C8H17

n

S

SF

OO

S

S

O

O n

PDTSTPD, 1.7eV,

7.3%, - NRCC (Tao)

S

Ge

S

S

NO O

C8H17

n

PDTGTPD, 1.7eV,

8.5 %, - UF (Reynolds & So)

PTB7, 1.6eV,

9.2 %,

-U Chicago (Yu)

-SCUT (Cao)

PBDTTT-CT,

1.6eV, 7.6 %,

- ICCAS (Hou)

S

S

S

S

N

NSe

SeO

O

nS S

O

NS

N

F F

* *

n

PDTP-DFBT, 1.4eV,

8.0 %, - UCLA

(Yang) & SCC

PBDTT-SeDPP,

1.4eV, 7.2 %,

- UCLA (Yang) 6

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UCLA

PTB-7 PTB-7Th polymers &

Inverted structure

H. Wu, Y. Cao et al. Nature Photonics (2012) & (2015)

State-of-the-art OPV UCLA - Morphology, Materials, Interfaces & Architecture

9.94% PCE Certified by CPTV

Jsc: 17.42 mA/cm2 Voc: 0.794V

FF: 71.9% PCE: 9.94%

YY LABs

UCLA8

hn>Eg

Focus Now: Polymer Tandem Solar Cells

Enhanced Absorption Reduced Thermal Loss

G. Dennler et al., Adv. Mater. 20, 579 (2008).

J. B. You et al., Prog. Polym. Sci. 38, 1909-1928(2013).

YY LABs

UCLA9

ITO/Glass Wide band gap

Tunneling Junction

Low Band Gap

Electrode

Polymer Tandem Solar Cells

YY LABs

UCLA

10 J. You, G. Li, Y. Yang et al., Nat. Communications, 4, 1446

(2013).

10.6% Polymer Tandem Solar Cells

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UCLA

Eg=1.58 eV

Mid-BG

Eg=1.38eV

Low-BG

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Eg=1.90 eV

Wide-BG

300 400 500 600 700 800 900 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4N

orm

aliz

ed a

bso

rpti

on

(a.

u.)

Wavelength (nm)

P3HT PTB7-Th PPDT-DFBT

0.0

2.0x1021

4.0x1021

Ph

oto

Flu

x (N

um

ber

/m2 /s

/nm

)

Triple-junction Polymer Solar Cells

C. C. Chen et al., Adv. Mater. 26, 5670 (2014).

YY LABs

UCLA

C. C. Chen et al., Adv. Mater. 26, 5670 (2014).

Triple-junction Polymer Solar Cells

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Voc=2.28 V Jsc=7.63 mA/cm2

FF=66.4% PCE=11.6%

YY LABs

UCLA

Schematic of the TOPV device architecture.

Photograph of a TOPV device achieved at UCLA.

R. Zhu.; et al., ACS Nano, 2012 C. Chen et al. EES 2014

4% PCE at 70%T, and 7.2% PCE at 45%T (Tandem)

UCLA Transparent OPV (TOPV)

YY LABs

UCLA14

Solar Energy from every Window

Solar Energy for every Gadget

“Invisible” Power

UCLA TOPV – Potential Applications

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UCLA

a-Si:H/OPV Hybrid Tandem Cells

Kim J, Yang Y et al., Nat. Communication (2015) 15

Glass/AZO

a-Si

Tunneling junction

OPV

Electrode

10.5%

6.1% 7.8%

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UCLA

0

2

4

6

8

10

12

14

16

18

20

PC

E %

05/13 07/13 09/13 01/14

Next: Perovskite Solar Cell Research at UCLA

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17-19%

1. Perovskite film growth - Vapor-assisted solution process - Film reconstruction with Moisture

2. Materials properties - Defect analysis and passivation - Effects of Chlorine

3. Interface Engineering - Efficient carrier path - Transport materials design

Timeline

YY LABs

UCLA

Film Formation & Interface Engineering

Y. Yang et. al., Science, 2014, 345, 542.

TiO2 Y:TiO2

ITO ITO/PEIE

4.6 eV 4.0 eV

Charge generation

Charge transport

Charge collection

Carrier dynamics High efficiency

• Grown in 30% humidity • Reference

Y-TiO2

TiO2

• With PEIE • Without PEIE

Substrate CH3NH3PbX3

moisture

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UCLA

Materials growth: Vapor Assisted Solution Process

VASP takes advantage of: Good film compatibility of PbI2

Low sublimation point of CH3NH3I Fast reaction between PbI2 and

CH3NH3I

Gas

Solid

CH3NH3PbI3: PbI2(inorganic) + CH3NH3I(organic)

Y. Yang et. al., J. Am. Chem. Soc, 2014, 136, 622. 18

YY LABs

UCLA

Monolithic Integration Tandem Cell

Polymer cell

IR-absorption

Perovskite cell

Visible-absorption

Perovskite/OPV Double-Junction Tandem Cell

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YY LABs

UCLA

Fast and low temperature processed perovskite film

Shorten the reaction time from 1 h to 5 min, at 100 °C C. C. Chen, Y. Yang* et al., Mater. Horiz., 2015, DOI: 10.1039/C4MH00237G. 20

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UCLA

Summary • Pursuing Game-Changing PV technologies – solution

process

• OPV is still an attractive PV technology, particularly in some special applications, but it needs breakthroughs to break the 15%PCE barrier.

• Perovskite is a promising technology, but needs to improve the basic understanding of many issues: mechanism(s), hysteresis, Pb-containing, stability….

• New Technology - early stage. We need supports from both government and industry to keep the momentum going.

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UCLA

YY Group today, 2015

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YY LABs

UCLA

Acknowledgment

Dr. Huanping Zhou Dr. Qi Chen Dr. Jingbi You Dr. Yongsheng Liu Dr. Ziruo Hong Dr. Johnny Chen

Keith Emery (NREL)

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