Department of PhysicsClarendon LaboratoryParks RoadOxfordOX1 3PU

e-mail: james.ball@physics.ox.ac.ukPhotovoltaics and

Optoelectronic Devices Group

Metal Halide Perovskite Solar Cells

Henry J. Snaith

henry.snaith@physics.ox.ac.uk

Can Solar Energy Power the Planet?

Comparative size of earth

Area → world’s current (thermal equivalent) primary energy*, in good conditions, from

Biomass230% of contiguous USA

Wind30% of contiguous USA

Solar4% of contiguous USA

*Average power:18.5 TWh or 7 TWe

Silicon Solar Cell (25% efficient)

Charge generated in p-type regionRequirement to maximise minority carrier (n) diffusion length (thickness ~300 μm)

p-n junction simply to enable charge collection selectivity

c-Si solar cell Originally invented in Bell Labs in 1954

Production of silicon and silicon wafersExpensive, high-energy process generating high levels of waste material

Coke reduction in arc furnace at

1800 °C

Disolve in HCI at 300 °C + distillation

Chemical refinement

Siemens processat 900 °C

Modified Siemens process

SandSiO2 + C

Metallurgical Grade

Silicon (MG Silicon)

Hydrogen Chloride

HCIHCI Hydroge

nHigh purity Trichlorosila

neHSiCl3 High purity

polysilicon ∼9N

Polysilicon ∼6-7NUpgradedMG silicon >5N

Various Gasses

Electronic-grade

Solar-grade

Solar grade

Polysilicon

Melting Czochralski

pulling

Cutting/

squaring

Squared

ingot

Wire sawing

Cleaning Wafer

Wings, top and tail recycling/etching

Slurry recycli

ng

from sand siliconto

from silicon waferto

What are Perovskite Solar Cells?

All materials with the same crystal structure as CaTiO3, namely ABX3, are termed perovskites.

Park et al. Nanoscale 2011 Nanoscale, 2011,3, 4088-4093

Tsutomu Miyasaka et al. J. Am. Chem. Soc. 2009, 131, 6050-6051

J. Ball et al. EES 2013

“Quantum dot” absorber to thin film semiconductor

The first examples showed small quantum dots, our route showed highly crystalline thin film

Efficient Planar Heterojunction Solar Cells

Remarkable efficiency rise

1970 1980 1990 2000 2010 20200

10

20

30R

ecor

d ef

ficie

ncy

(%)

Year

GaAs c-Si CIGS CdTe Perovskite

A thin film “double” heterojunction

Compact TiO2

AgSpiro-MeOTAD

Perovskite

FTO

Glass

Organic n-type in regular structure

K. Wojciechowski, et al. ACS Nano 2014

“Inverted” Perovskite Solar Cells

Negligible Hysteresis“Instant” rise to max power

Best architecture for MAPI Cells

J. T-J Wang et al. Submitted

Solar Cell Performance

ControlHPA

HPAControl

Control (FB-SC)Control (SC-FB)HPA (FB-SC)HPA (SC-FB)

ControlHPA

HPAControl

HPA

Perovskite stability

Bulk Thermal Stability of MAPbI3

T. Baikie et al. J. Mater. Chem. A, 2013,1, 5628-5641

Thermal Stability

Heating CH3NH3PbI3-xClxat 85 degrees in air (RH ~ 50%)

Perovskite decomposes to PbI2

What are the cation options?

Goldshmidt Tolerance factor

FAPbI3Planar Heterojunction Solar cells

0.0 0.2 0.4 0.6 0.8 1.0-5

0

5

10

15

20

25

Jsc = 23.3mAcm-2

Voc = 0.94VFF = 0.65PCE = 14.2%

Cur

rent

den

sity

(mA

cm-2)

Voltage (V)

400 500 600 700 800 9000

20

40

60

80

100

Ext

erna

l Qua

ntum

Effi

cien

cy (%

)

Wavelength (nm)

With Increased pH

Good solar cell operation and red shifted absorption.Loss in voltage a little larger than MAPbI3-xClx, but may be overcome.

G. Eperon et al. EES 2014

Thermal Stability: Formamidinium

@150 ̊C most of the methylamonium CH3NH3 (MA) is lost and the MAPbI3 perovskite PbI2

For Formamidinium, HC(NH2)2+

(FA) the film is stable to heating at 150 ̊C for over an hour in air.

Phase instability of FAPbI3:

Koh, T. M. et al. J Phys Chem C (2013)

Can be overcome by mixing MA with FA, (for instance see Norman Pellet et al. Angew Chem int Ed 2014, 53, 3151) but then still retain thermal instability of MA perovskite.

Economies of Scale

Staggering drop in the price of PV electricity

It is now “inevitable” that PV will become the cheapest form of generating electricity (source Bloomberg)

(natural Gas)

Tandem Solar Cells

Eg. See papers by Baliff et al and McGehee et al,

Tuning the band gap with mixed anions

5.9 6.0 6.1 6.2 6.3 6.4

1.4

1.6

1.8

2.0

2.2

2.4

Tetragonal

y=1

Å

g(

)

Pseudocubic lattice parameter a* ( )

y=0

Cubic

G. Eperon et al. EES 2014

Formamidinium trihalogenplumbate (iodide-bromide mixed halide)

Another problem with mixed halides

Photo-induced halide segregation results in low gap impurity phases

Erik t. Hoke et al DOI: 10.1039/C4SC03141E (Edge Article) Chem. Sci., 2015, 6, 613-617

Adding a small amount of Cs to FAPb(I1-xBrx)3

Ability to crystallise throughout the entire I-Br compositional range

No shift in PL for FA0.83Cs0.17Pb(I0.6Br0.4)

Blasted at 5Wcm-1

Mobility and electronic disorder

Theoretical Voc max ~ 1.42V(in the radiative limit)

PLmaxTauc-Eg

For modelling Voc see K. Tvingstedt et al., Radiative efficiency of lead iodide based perovskite solar cells. Sci. Rep. 4, 6071 (2014).

Solar cell operation

0.0 0.2 0.4 0.6 0.8 1.0 1.202468

10121416182022

Jsc: 19.4 mA cm-2

Eff: 17.9 %Voc: 1.19 VFF: 78.5 %

Cur

rent

Den

sity

(mA

cm

-2)

Voltage (V)

A

0 2 4 6 8 10 12 14 16 180

10

20

30

40

50

60

N total: 220Median: 13.4Std Dev: 4.5

Sam

ple

Cou

nts

JV PCE (%)

A

Simple 4-T configuration

A

-(p)a-Si:H (~10nm)

(n)c-Si (~200µm)

ITO (80 nm)

(n+)a-Si:H (~30nm)

Al

(i)a-Si:H (<10nm)

(i)a-Si:H (<10nm)

+

Glass

FTO

SnO2/PCBM

Perovskite

Spiro-OMeTAD

ITO

Buffer layer

Performance under simulated sun light

D. McMeekin et al. Science 2016 DOI 10.1126/science.aad5845

All Inorganic Perovskites

CsPbX3

Crystal structure ABX3

H. L. Wells, Zeitschrift fur Anorg. Chemie (1893), 3, 195–210.

C. K. Moller, Nature (1958), 182, 1436.

CsPbBr3

L. Protesescu, S. Yakunin, … M. V Kovalenko, Nano Lett., (2015), 15 (6), 3692–3696.

C. C. Stoumpos, C. D. Malliakas, … M. G. Kanatzidis, Cryst. Growth Des. (2013), 13, 2722−2727.

34

Introduction to CsPbX3

Thermal stability

Reversible transitions

35

adapted from Sharma et al.

Cubic Perovskite

(Tetragonal)

Orthorhombic non-perovskite phase at RTCsPbBr3

130 °C

CsPbI3316 °C

Phase diagram: S. Sharma, N. Weiden, & A. Weiss, Zeitschrift Für Physikalische Chemie, (1992), 175 (1), 63–80.

Evaporation: S. Kondo, T. Sakai, H. Tanaka, T. Saito, Phys. Rev. B (1998), 58, 11401–11407.

CsPbI3: One-step method

Cubic Perovskite

CubicPm-3m

Black phase

>310oC

OrthorhombicPnma

Yellow phase

CsPbI

Room tempCsPbI3

316 °C

G. E. Eperon, G. M. Paternò, R. J. Sutton, A. Zampetti, A. Haghighirad, F. Cacialli, H. J. Snaith, J. Mater. Chem. A (2015), DOI: 10.1039/C5TA06398A.

G. E. Eperon, G. M. Paternò, R. J. Sutton, A. Zampetti, A. Haghighirad, F. Cacialli, H. Snaith, H. J. Mater. Chem. A (2015), DOI: 10.1039/C5TA06398A.

One-step series: CsPb(IxBr1-x)3

Bandgap is tuneable with bromide content Cubic Perovskite

600 625 650 675 700 725 750 775 8000.0

0.2

0.4

0.6

0.8

1.0

PL

Inte

nsity

(nor

mal

ised

)

Wavelength /nm

x = 1 x = 0.93 x = 0.87 x = 0.8 x = 0.73 x = 0.67

400 450 500 550 600 650 700 750 8000.0

0.5

1.0

1.5

2.0

2.5

Abs

orba

nce

/a.u

.

Wavelength /nm

x = 1 x = 0.93 x = 0.87 x = 0.8 x = 0.73 x = 0.67

1 95c

ba

d

One-step series: CsPb(IxBr1-x)3

38

Wavelength /nm

0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

1.75

1.80

1.85

1.90

1.95

y = 2.21 - 0.45 x

c

Abs

orpt

ion

onse

t; P

L pe

ak /e

V

Fractional iodide concentration 'x'

CsPbI2Br1.92 eV

38

Cubic Perovskite

600 625 650 675 700 725 750 775 8000.0

0.2

0.4

0.6

0.8

1.0

PL

Inte

nsity

(nor

mal

ised

)

Wavelength /nm

x = 1 x = 0.93 x = 0.87 x = 0.8 x = 0.73 x = 0.67

400 450 500 550 600 650 700 750 8000.0

0.5

1.0

1.5

2.0

2.5

Abs

orba

nce

/a.u

.

Wavelength /nm

x = 1 x = 0.93 x = 0.87 x = 0.8 x = 0.73 x = 0.67

1 95c

ba

d

CsPbI2Br film properties

350 °C 400 °C250 °C 300 °C

100 °C 150 °C 200 °C

D. M. Trots and S. V. Myagkota, J. Phys. Chem. Solids, (2008), 69 (10), 2520–2526.

Stability in air: CsPbI2Br vs CsPbI3

40 40

0 10 20 30 40 50 60 70 800.2

0.3

0.4

0.5

0.6

0.7d

Abs

orba

nce

/a.u

.

Time /minutes

x = 0.67: CsPbI2Br x = 1: CsPbI3

Compositional Stability (85 °C in 25% RH)

400 450 500 550 600 650 700 750 8000.0

0.5

1.0

1.5

2.0

2.5

b

Abs

orba

nce

/a.u

.

Wavelength /nm400 450 500 550 600 650 700 750 800

0.0

0.5

1.0

1.5

2.0

2.5

Abs

orba

nce

/a.u

.

Wavelength /nm

0 60 120 180 2400.0

0.2

0.4

0.6

0.8

1.0

CsPbI2Br (627 nm)

Abs

orba

nce

(nor

m.)

Time /minutes0 60 120 180 240

0.0

0.2

0.4

0.6

0.8

1.0 MAPbI2Br (670 nm)

Abs

orba

nce

(nor

m.)

Time /minutes

a

CsPbI2Br After

10 20 30 40 50 60

Position, /2θ, degrees

CsPbI3 Reference

dc

Inte

nsity

/a.u

.

Inte

nsity

/a.u

.

CsPbI2Br Before MAPbI2Br Before

MAPbI2Br After♦

10 20 30 40 50 60

Position, /2θ, degrees

MAPbI3 Reference

CsPbI2Br devices

Shockley–Queisser limit for 1.92 eV bandgap:

JSC = 16.3 mA cm-2

VOC = 1.63 V

W. Shockley, H. J. Queisser, J. Appl. Phys. (1961), 32, 510.

0.0 0.2 0.4 0.6 0.8 1.0 1.2-2

0

2

4

6

8

10

12

14

7.8 %

Cur

rent

den

sity

/mA

cm-2

Voltage /V

9.8 %

SPO

c

0

2

4

6

8

10

12

Time /s

Cur

rent

den

sity

/mA

cm

-2

5.6%7.1 mA cm-2

JSC (mA cm-2)

PCE (%)

VOC (V) FF

Best 11.89 9.84 1.11 0.75

Average 11.82 6.02 0.85 0.57

0 50 100 150 200 250 300012345678910

PC

E /%

dHold at VMPP

Commercialisation

Device and mini-module development Target: Develop stable and efficient materials stack

Develop processing methodology to deliver

Efficient perovskite/Silicon tandem cells at

high yield

Partner with existing Si-PV industry to

manufacture

Targeted Market

Combining Perovskites and Si in a tandem architecture could lead to >30% efficient modules

Example of possible structure

Structural Stability: FA perovskiteFAPbI3 Trigonal and Hexagonal phases possible at RTP

• Black (desired) 3D trigonal phase stable at 150oC in bulk and film

Koh, T. M. et al. J Phys Chem C (2013)

• 54 cycles -40 to +85oC (6hour cycle)

54 cycles

0

20

40

60

80

100

120

-300 200 700 1200

Nor

mal

ised

pero

vski

te C

olou

rIn

tens

ity (%

)

Stressing Time (hours)

Control(140)Control(115)A

B

C

Moisture sensitivity

Interlayer assembly only

Encapsulation selection using 1000hr 85oC/85% baseline

Perovskite layer degradation by moisture ingress after early lamination failure

350hrs0 hrs

Moisture ingress accelerates degradation

Cover Glass

Interlayer

Perovskite Film

Module Glass

Encapsulate the devices well

Full sun light soaking 60⁰ C

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 500 1000 1500 2000

Nor

mal

ised

Pm

ax

Hours elapsed

Solar cells aged under load with no UV filter at 60 ⁰C

Next Stage:

Scale up cell size to full 6” wafer.Push efficiency of 2T tandem beyond 25%Develop manufacturing process

Perovskite on Silicon 2T tandem

How do perovskites compare to other technologies?

Operating loss

19% cell170mV

Pabitra Nayak and D. Cahen and co workers

FASn0.5Pb0.5I3

1.74eV Cell

Acknowledgements

Funding EPSRC, ERC & FP7, Oxford John Fell Fund, Oxford Martin School, Royal Society.

Collaborators:Perovskites:Takuru MurakamiTsutomu Miyasaka

Oxford:Michael JohnstonLaura HerzRobin NicholasVictor BurlakovAlan Goriely

Swansea: David Worsley, Tristan Watson et al.

Milan:Annamaria PetrozzaGiulia Grancini et al.

Cambridge: Richard FriendFelix Deschler Michael PriceAditiya et al.

ICL Franco Cacialli

Helholtz:Lars KorteBernd Reiche

LoughboroughPatrick IsherwoodMike Walls

+ others