techniques to study degradation in pvs · major kinds of degradation in perovskite solar cells...

Techniques to Study Degradation in PVs

K.S. Narayan

Jawaharlal Nehru Centre for Advanced Scientific Research

Bangalore India

[email protected]

Inorganic Semiconductors Band transport High mobility large carrier diffusion length

organic Semiconductors Tunable Band-gap Solution Processable Low temperature, low cost

manufacturing

Organic inorganic halide Perovskite

Organo Metal Halide Perovskite

The rapid evolution of highly efficient perovskite solar cells Correa-Baena et al EES 2017

Degradation in Perovskite Solar Cells

Major kinds of degradation in perovskite solar cells

➢Oxygen induced degradation

➢Light induced degradation

➢Moisture induced degradation

➢Temperature induced degradation

➢Thermal and electric field induced intrinsic degradation

Taame Abraha Berhe, Bing-Joe Hwang, Organometal halide perovskite solar cells:degradation and stability, Energy Environ. Sci.,2016, 9, 323 4

“Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment,” RoHS1 in 2003 and the subsequent RoHS2 in 2011, which are also known as the “lead-free directives.”The RoHS takes into account the more recent understanding of long-term risks associated with continuous exposure to low levels of toxic heavy metals. Specifically, it restricts to 0.1% in weight the maximum concentration of lead in each homogeneous material contained in any electronic devices, i.e., the perovskite within a PSC. Unfortunately, all the halide perovskites that have been so far demonstrated as effective photovoltaic materials contain more than 10% lead in weight.

Lead Content of Sindoor, a Hindu Religious Powder and Cosmetic: New Jersey and India, 2014–2015

•American Journal of Public Health (ajph) October

2017

Results. Analysis determined that 79 (83.2%) sindoor samples purchased in the United States and 18 (78.3%) samples purchased in India contained 1.0 or more micrograms of lead per gram of powder. For US samples, geometric mean concentration was 5.4 micrograms per gram compared with 28.1 micrograms per gram for India samples. ..Of the examined US sindoorsamples, 19% contained more than 20 micrograms per gram of lead (US Food and Drug Administration [FDA] limit); 43% of the India samples exceeded this limit.

Conclusions. Results suggested continued need for lead monitoring in sindoorin the United States and in sindoor carried into the United States by travelersfrom India, despite FDA warnings.

http://ajph.aphapublications.org/loi/ajph

http://ajph.aphapublications.org/toc/ajph/107/10

T= 293 K a = b = 8.849 Å , c = 12.642 ÅAd = 104.2 mg/m2

T =400 Ka = b = 6.3115 Å , c = 6.3161 ÅAd = 410 mg/m2

Note : In general T > 330 K Cubic phase160K < T <330 K Tetragonal PhaseT <160 K Orthorhombic Phase

References : 1) Fabini, Douglas. "Quantifying the potential for lead pollution from halide perovskite photovoltaics." (2015): 3546-3548.

2) Stoumpos, Constantinos C., Christos D. Malliakas, and Mercouri G. Kanatzidis. "Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties." Inorganic chemistry 52.15 (2013): 9019-9038.

Health hazards of methylammonium lead iodide based perovskites: cytotoxicity studiesIness R. Benmessaoud,a Anne-Laure Mahul-Mellier,b Endre Horváth,a Bohumil Maco,b Massimo Spina,a Hilal A. Lashuel*b and Làszló Forró*a Author affiliationsAbstract

New technologies launch novel materials; besides their performances in products, their health hazards must be tested. This applies to the lead halide perovskite CH3NH3PbI3 as well, which offers fulgurate applications in photovoltaic devices. We report the effects of CH3NH3PbI3 photovoltaic perovskites in human lung adenocarcinoma epithelial cells (A549), human dopaminergicneuroblastoma cells (SH-SY5Y) and murine primary hippocampal neurons by using multiple assays and electron microscopy studies. In cell culture media the major part of the dissolved CH3NH3PbI3 has a strong cell-type dependent effect. Hippocampal primary neurons and neuroblastoma cells suffer a massive apoptotic cell death, whereas exposure to lung epithelial cells dramatically alters the kinetics of proliferation, metabolic activity and cellular morphology without inducing noticeable cell death. Our findings underscore the critical importance of conducting further studies to investigate the effect of short and long-term exposure to CH3NH3PbI3 on health and environment.

➢ Imperative and quantitative signatures of degradation preferably in-situ conditions will be useful.

➢ Reliable tool to diagnose at a relatively early stages

➢ Lack of clear understanding of the multitude of defect evolvement processes and their role in carrier transport mechanisms in perovskite-based devices.

9

IEA: “Review of Failures of Photovoltaic Modules” 2014

Transport ModelsDrift - Diffusion

∂n∂t = ∇・ (μnn∇φ + Dn∇n)+G−R

∂ p∂t = ∇・ (Dp∇p−μpp∇φ)+G−R

∇・ (ε∇φ) = −q(p−n+Nd)

the carrier concentrations in terms of quasi-Fermi levels

J = drift + diffusion

AmbipolarCoupled

Traps and Defects

Recombination Shockley-Read-HallMany sources for recombination in solar cells. In General,recombination at low excitation levels arises primarily from defect or trap states.

Monomolecular recombination: 1st order kinetics -minority carrier concentration when one carrier type predominates. R – Rate of recombination

where nt (pt) is the density of electrons (holes) in filled traps and τn (τp) is the time for electrons (holes) to be captured by trap states.

We can explicitly write nt as the product of the density of traps and a capturecross-section, tn = ntBn

Neeman 3rd edn

Surface and grain boundary recombinationSurfaces and grain boundaries represent regions where there are likely to be a large concentration of trap states, due to broken bonds and higher concentrations of impurities.Because the traps are concentrated in a small space, it is more useful to consider the density per unit area than per unit length.

We can define the surface recombination velocities, Sn,p by multiplying the density of traps per unit area, Nt with the capture cross-section, Bn . The recombination times, τn,p are equal to the product of the thickness of the layer (Δx) and Sn,p

Band-to-band recombination involves the recombination of an electron and hole withoutan intermediate stage, and therefore is bimolecular in the low-doping case. Balancingwith band-to-band generation in equilibrium, we have the net rate of recombination asRbb = B(np−n2

i) for B the bimolecular recombination constant. In direct-bandgapsemiconductors, this process is optically generated, otherwise it may also involve phononabsorption or emission.

14

dAtAJtI

At

tAQtAJ

,

1,,

nqQ

constantt

n

constant0

t

n

Source of noise in kinetic processes, time-

dependent terms?

Reasonable to expect noise in ISC of BHJs ?

Sources of noise in Solar Cells

14-Dec-17 15

ij

ij

B

ij

ij

ij

εTk

a

ra

for 1

for exp

2exp0

Origin of fluctuation : Microscopic model

Ltr or tr

No

. of

cou

nts

Etr = 0

E

Shallow traps

Deeptraps

ij

X= 0 X= LEtr = 0

E

Shallow traps

Deeptraps

ij

X= 0 X= L

Photocurrent Iph(t) : CW illuminationFluctuation d Iph(t) = Iph(t) – Iph(t)Noise powerTypically 100 samples,100ms sequences with4ms interval measurements

17

Noise Models

➢ Primary reason for noise , conductivity fluctuations

➢ For constant mobility,

Change in conductiviyy related to fluctuation in number density of charge carriers,

McWhorter Model

➢ For a fixed number density,

Change in conductiviy related to fluctuation in mobility of charge carriers,

Hooge Model

m en

ne m

m en 𝑺𝑰 𝒇 = 𝑨𝒏𝑰𝛃

𝒇𝜶

18

Current fluctuation in solar cell

light

dark

G/eV1P*

P

huP+…A-

Separatedcharges

Boundpolaron pair

P+ + A-Transport

to electrodes

Bimolecularrecombination (ns – ms)

Geminate Recombination (ps – ns)

19

Noise measurement as a function of

✓ Temperature✓ Intensity✓ Device efficiency

M. Bag, N. S. Vidhyadhiraja and K. S. Narayan (Appl. Phys. Lett. 2012)

Anode

Bulk-heterostructure solar cells

20

Temperature Dependence of Fluctuations

➢ Current or conductivity fluctuations, Δσ =Δ(qnµ) are related to the fluctuations in charge carrier density (ΔN model) or mobility fluctuations (Δµ model)

𝑺𝑰 𝒇 = 𝑨𝒏𝑰𝛃

𝒇𝜶

➢ The current noise spectra are usually analyzed by Hooge’s empirical

relation and is expressed as:

Here ‘An’ is the noise magnitude coefficient.

➢ Further analyses can be made in terms of relative or normalized power

spectrum density (NPSD) by normalizing the power spectrum density by Iβ.

𝑺 𝒇 ∝𝑺𝑰 𝒇

𝑰𝜷∝

𝟏

𝑵 𝒇𝜶

➢ The generation-recombination noise originates from the number

fluctuation. Its PSD can be expressed in the Lorentzian form:

𝑺𝑰(𝒇) =𝑺𝟎

[𝟏 + 𝟐𝝅𝒇𝝉𝟐]

where S0 is the part of SI(f) which is independent of the frequency, as seen at

f < 1/ 2πτ. τ is the time constant related to a particular trapping state. 22

Materials and Methods

➢ FTO/TiO2/Perovskite/Spiro-MeOTAD

➢ FTO/C60 / Perovskite/ Spiro-MeOTAD

➢ FTO/polyTPD/Perovskite/PCBM/BCP

Fabricated in Clarendon Laboratory, Dept. of Physics University of Oxford (U.K.) 23

24

J-V characteristic

1/f noise as in the PSD under outdoor conditions

25

Poly(4-butylphenyl-diphenyl-amine)

N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-9,9′-spirobi[9H-fluorene]-2,2′,7,7′-tetramine, Spiro-OMeTAD 2,9-Dimethyl-4,7-diphenyl-1,10-

phenanthroline, BCPphenyl-C61-butyric acid methyl ester

Buckminsterfullerene

26

(a)

(b)

(c)

(1)- Ionic Samples

➢ KCl and LiClO4 solution➢NaCl+ AgNO3 solution➢PSS➢ Nafion➢PbI2 and CH3NH3PbI3

(2)- Dye-Sensitized Solar Cell

DSSC

27

28

Schematic representation of experimental setup used for noise spectroscopy

Solvent: Dimethylformamide (DMF)

30

Noise power spectrum density vs frequency plot for PbI2 in DMF solution

Noise power spectrum density vs frequency plot for CH3NH3PbI3 in DMF solution

Voc (V) Isc( A) Jsc mA/cm2 Imax( A) Vmax( V) Pmax mW Fill Factor Efficiency

0.669362 0.012236 2.447203 0.009858 0.533374 5.257901 64.1965 1.0516

31

Noise spectrum obtained from a typical DSSC cell

32Noise contribution from the ions is expected

of 0.6 V was Biasapplied for 60 s prior to illumination

Bias of (-1.2) V was applied for 60 s prior to illumination

Change in noise spectrum with variation in the device history

Time series data of three different structure under dark and light. (a)FTO/ TiO2/ CH3NH3PbI3/Spiro-OMeTAD/Ag (b) FTO/ C60/ CH3NH3PbI3/Spiro-OMeTAD/Ag (c) FTO/Poly-TPD/ CH3NH3PbI3/PCBM/BCP/Ag. The time duration for the capture of one data frame is 0.5 second and 80 frames in each dataset

33

Apoorva Singh, Suman Banerjee, Pabitra Nayak, Zhipping Wang, Jacob Wang H.J. Snaith and K.S. Narayan, Insights in to the microscopic and degradation processes in hybrid perovskite solar cells using noise spectroscopy and photocurrent scanning (Solar RRL – Wiley 2017)

Devices Standard deviation

Device 1 1.8 × 10−8

Device 2 8.4 × 10−9

Device 3 2.8 × 10−9

Representative image from a typical device, showing a linear dependence of Jsc on Intensity

The light intensity serves as a useful parameter to evaluate the transport process of the photo generated carriers

34

power spectrum density (PSD) SI(f) for different intensity/Jsc plotted against f.

J-V characteristics in forward

and reverse scan

FTO/ TiO2/ CH3NH3PbI3/spiro-OMeTAD/Ag

FTOTiO2 (ETL)

PerovskiteSpiro-MeOTAD (HTM)

Ag

35

Normalized power spectrum density ((S(f)), indicating a universal behavior and unified noise value at zero frequency.

Distribution function of current amplitude fluctuation histogram under dark and different intensities (Jsc values) of white light

FTO/ TiO2/ CH3NH3PbI3/spiro-MeOTAD/Ag

36

FTOTiO2 (ETL)

PerovskiteSpiro-MeOTAD (HTM)

Ag

J-V characteristics in forward and reverse scan

Power spectrum density (PSD) SI(f) for different intensities/Jsc

plotted against frequency

FTO/ TiO2/ C60/CH3NH3PbI3/spiro-OMeTAD/Ag

37

Normalized power spectrum density S(f)=(SI / I β(Hz)), unified noise behavior is seenat zero frequency.

Distribution function of current amplitude fluctuation histogram under dark and different intensities (Jsc values) of white light 38

FTO/ TiO2/ C60/CH3NH3PbI3/spiro-OMeTAD/Ag

FTO/Poly-TPD/CH3NH3PbI3 /PCBM/BCP

FTOPoly-TPD (HTM)

PerovskitePCBM (ETL)

BCP (ETL)Ag

39

J-V characteristics in forward and reverse scan

PSD at different intensities/Jsc values, device at the measurement had PCE of ~15%

PSD measured from the device, cell degradeddown to PCE of <0.1%. 1 to 5 represents intensities(0.45 mW/cm2, 9.8 mW/cm2, 18.6 mW/cm2, 23mW/cm2, and 52.4 mW/cm2).

Normalized power spectrum density S(f)= (SI / I β(Hz))


40

FTOPoly-TPD (HTM)


BCP (ETL)Ag

Parameters Device 1 Device 2 Device 3

FTO / TiO2 /

CH3NH3PbI3 / Spiro-

OMeTAD / Ag

FTO / C60 / CH3NH3PbI3 /

Spiro-OMeTAD / Ag

FTO /Poly-TPD /

CH3NH3PbI3 / PCBM /

BCP / Ag

Voc ( V) 0.91 0.88 1.04

Jsc

( mA/cm2)

16.51 2.61 21.85

Fill Factor 48.78 60.67 69.9

Efficiency

(η %)

7.32 1.39 15.96

α in 1/fα α~ 1.9

α~ 2 for lower f (<100Hz)

and α~1 for higher f.

At very low η (<0.1%),1/f is

uniform with α~ (1to 1.4)

α~ 1. In addition to

1/f,

G-R noise is observed.

at η <0.1%, uniform

1/f behavior with α~1

β in Iβ ~ (2 to 2.5) ~ 1.6 ~2

Summary of performance and noise parameters from representative devices of each structure.

41


42

Degradation studies: (a) J-V curve for different degradation stages (b)corresponding normalized noise power spectrum density (NPSD), S(f). η of15.96%, 7.83%, 4.57% and <1% corresponds to the measurements taken at 0 hr.,8 hrs., 16 hrs. and 32 hrs. respectively.

FTOPoly-TPD (HTM)


BCP (ETL)Ag

Background for Admittance Studies

• An electrically active defect reveals itself as a peak in the conductance G versus temperature T

• Peak in G/ω versus frequency ω curves

• as a step in the capacitance C versus T or C versus ω curves.

• A relation between the defect density of states and the frequency derivative of capacitance ωdC/dω versus ω - Walter et al (1196 JA. ApplPhys.)

44

Mott-Schottky plot for perovskite solar cells. The blue

line is an extrapolation to determine the built-in voltage.

Vbi (V) Nd (cm-3) W (cm)

Fresh 0.95 5.6x1015 7.5x10-5

Aged 0.87 8.6x1016 1.8x10-5

The slope of the extrapolation can be

used to determine the doping density Nd

depletion width W at Vbias = 0 V

TAS

45

a) Typical temperature dependence of the frequency-dependent

capacitance of a perovskite solar cell. b) Arrhenius plot of the

characteristic transition frequencies extracted from a) to extract the

defect activation energy of a perovskite solar cell.

the trap energy Ea and

the characteristic

transition frequency ω0

can be expressed as:

TAS

46

: tDOS for perovskite solar cells before and after aging.

the frequency dependent

capacitance can be used to

determine the energetic

profile of the tDOS

The resultant graph shows the tDOS as a function of energy related to the

valence band of the perovskite. These graphs have been extracted from

multiple devices. Integration of the tDOS along the horizontal axis gives the

trap density in the perovskite.

Trap density evaluation using TAS

Experiments performed by Dr. Zhipping Wang and Dr. Pabitra Nayak, Prof. Snaith’s Lab, Univ. of Oxford (U.K.)

Evolution of noise spectrum with degradation as seen in conventional structure of hybrid perovskite solar cells

FTO/TiO2/ C60/ CH3NH3PbI3/spiro-OMeTAD/Ag

47

➢ Noise magnitude relative to the signal directly correlates

with the performance parameters, with the noise levels

increasing with degradation.

➢ All the devices exhibit 1/fα behavior in the range < 1 kHz

➢ The exponent α and f range over which 1/f response is

observed appears to depend on the transport processes

and the associated disorder in the system.

➢ the noise mechanism of devices under operation with

high J (at high light intensity) is different from that at low

J.

➢ This intensity dependent noise response appears to be

dependent on the device structure and is different from

the different geometry.48

Introduction…………

Generation:

• Photoactive metal/polymer schottky interface

• External electric field

• Excitation wavelength of light

Transport:

● Poisson’s Eqn ● Current Density Eqn ● Continuity Eqn

2

2

0

x

nD

x

nE

x

En

nnG

t

n p

n

p

nnp

n

pp

n

p

mm

Generation &

Recombination RateDrift Diffusion

r

ITO

stri

p

PolymerAl

holes

laser

r

h+

r

ITO

stri

p

PolymerAl

holes

laser

r

h+

LPE: A non- uniform illumination of schottky (or p++ - n / p – n++ junction)

interface compensate built- in barrier field locally, which results in a lateral

photo-electric field in the plane of interface

Ln=(Dnn)1/2

x

np(x)

np0

)exp(0 00 npppp Lxnnnxn

0

2

1

21 .

.

e

tTktDr nB

n

m

Einstein Relation: Dn = mnkBT/e ?

2

2

0

x

nD

x

nE

x

En

nnG

t

n p

n

p

nnp

n

pp

n

p

mm

Introduction…………

Diffusion Process: Carrier Transport Studies

Al

Polymer

laser

electronsr

ITO

r

e-

Al

Polymer

laser

electronsr

ITO

r

e-

r

e-

E = 0

Low intensity

Steady State (dn/dt = 0)

μτe

TkL

)Lr( exp 0nrn

B2

d

d

Ld=(D)1/2r

n(r)

n0

Materials

Semiconducting polymers:

O

O

n

S

S

S

S

Poly(3-hexylthiophene) (P3HT)

Poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-

phenylene vinylene) (MEHPPV)

Poly(9,9-dioctylfluorene-alt-bithiophene) (PFO - TT)

**

nS

S

S

S

S

S

Materials………

P3HT

➢ Orientation on Hydrophobic Surfaces (HMDS, APS and OTS)

➢ Micro-nano crystalline domains

➢ 2D lateral transport (Interchain & intrachain hopping)

➢ High hole mobility

O

O

n

Materials…………

MEHPPV

➢ Disorder system

➢ Conformational configuration of phenyl rings

➢ Random flexible coiled polymer chains

➢ Poor carrier mobility

Materials…………

PFO – TT

➢ Nematic liquid crystalline phase

➢ Spatially anisotropic electric transport

➢ Higher mobility in oriented direction

➢ Ambipolar behavior in oriented samples

ry

rubbed direction || to rx

PFO – TT chainsry


PFO – TT chains

**

nSS

Experiments……….(Spatial Dependence)

(b)

SEM

Scanning Probe Photocurrent Contrast Image

Photocurrent Profile

Photocurrent

Cover glass

ITO strips

Al

60X

polymer

Cover glass

ITO strips

Al

60X

polymer

(a) 5 mm

32.80 pA

31.60 pA

(c)

(b)

ITO

31.10 pA

33.65 pA

31

32

33

34

0 10 20 30

r(mm)

I light(p

A)


Al

Polymer

laser

electronsr

ITO

r

e-

Al

Polymer

laser

electronsr

ITO

r

e-

r

e-

r

ITO

stri

p

PolymerAl

holes

laser

r

h+

r

ITO

stri

p

PolymerAl

holes

laser

r

h+

0

50

100

0 40 80 120

electrons

holes

Ilig

ht(n

orm

.)

0

50

100

0 5 10 15

electrons

holes

electrons

holes

Ilig

ht

0

50

100

0 10 20 30

r (mm)

I lig

ht

O

O

n

S n

**

n

S

S

C8H17C8H17

(b)

(c)

(d)

Scanning Directions

1. Ldh(rx)

2. Lde(rx)

3. Lde(ry)

4. Ldh(ry)

PFO-TT

ITO

Rubbed Polyimide

12

3

4

rx

ry

|| to rx

|| to ry

Light Polarization Dependence


20

40

60

80

100

0 200 400 600

holes

rx

ry

r mm)

I ligh

t (n

orm

. u

nits)

0

50

100

0 60 120 180

electrons

ry

rx

r (mm)

I ligh

t

ry


PFO – TT chainsry


PFO – TT chains

Structurally Induced Electrically Anisotropic Charge Carrier Transport

Results

Polymer decay length

(Lde) from Ile(r)decay length

(Ldh) from Ilh(r)mhh/mee

P3HT 8.3 mm 51.1 mm 37.54

MEHPPV 2.8 mm 6.8 mm 5.96

unoriented PFO

– TT

3.9 mm 14.1 mm 13.07

PFO – TT (rx)

polarization || to

rx

87.3 mm 134 mm 2.36

PFO – TT (ry)

polarization || to

rx

25.5 mm 50.3 mm 3.89

Decay lengths for electrons (Lde) and holes (Ldh)

Kabra and Narayan Adv. Mat. 2008

Wd

qVbi

EF

HOMO

LUMO

+

-

Al P3HT

Wd

qVbi

EF

HOMO

LUMO

+

-

Al P3HT

Wd

qVbi

EF

HOMO

LUMO

++

--

Al P3HT

D. Kabra et al. Appl. Phys. Lett. 85, 5073, 2004.

Polymer / Al schottky interface

Net lateral photovoltage

X

ph(x)

Depletion layer

AuL AuR

Light

Polymer

L / 2 L / 2

Al

Introduction…………(LPE)

RL

Polymer

L

Polymer

L = R

- -

+++

++

-

+ ++

--- - - - - - -- --- - - - - - - --

+++

+

-

+ ++

+

R

L > R

phL phR

Al

Polymer

Chopped

laser

L

w

Device Fabrication…………

(i)

(ii)

(iii)

(iv)

(vi)

(vii)

Substrate

(Glass)

Physical Shadow Mask

Metal (Cr - Au) Deposition

Polymer Coating

(Spin coating)

Physical Shadow Mask

Metal (Al) Deposition

10 mm

1 mm

De

w

700 nm

Model

Polymer/Al schottky interface

(0,0) (0,1) (0,2)

(1,2)

(2,2)

Iph

Rsp01

Csp01

Ct

Ct

Ct

CtCtCt

Ct = Transverse Capacitance

Rsp= Spreading Resistance

Csp= Spreading Capacitance

Cell Size = 10 mm


controller

50 X 633 nm

543 nm

10X

Interface box

Lock-inx

Lock-in

PD

PSD

1D Optical Profiling Setup


Solar cell

type

PSDs

Lateral photovoltage- in Hybrid Perovskites

ΔVp

h

)(xph

x

L/

2

L/

2Au Au

Glass

MAPbI3 Depletion

layer

x=0

mm x=L

mm

Light

ehe

e

ee e e e e e e e ee IT

O

L > R

h

h h

)(xph x

L/

2

L/

2Au Au

Glass

x=0

mm x=L

mm

Light

ehe

e

ee e e ee e e ee IT

O

L < R

h

h h

e

MAPbI3

ΔVphφL

φR φLφR

Page 26

Light

Experimental Setup

Page 27

(a

)

xy

Glass

Vph1

, Lock-in Amplifier21)( phphph VVxV

Vph2

AuAu

50X

0.70 NA

(b

)

Light

ΔVp

h)(xph

x

ITO

L/2 L/2Au Au

Glass

MAPbI3

Depletion layer

x=0 mm x=3

mm

Chapter 4

ΔVph(x)=differential lateral photo voltage

Spatial dependence of differential lateral photo voltage - I

Page 28

A

u

A

u

ΔV

ph

(mV

)

(a

)

ΔV

ph

(mV

)

(b

)

Chapter 4

Spatial dependence of differential lateral photo voltage - II

Chapter 4

Page 29

Transient response of PSD

light

Oscilloscope

Au

Au

𝐼 = 𝐼0exp(−𝑡

𝜏)

τ= 43 µs

Page 30

τ, independent of beam position

❖ Demonstrated position sensing devices (PSD) based on a simple geometry using active

HOIP layers.

❖Linear response of the differential signal covering a wide wavelength range at reasonable bandwidth

❖High spatial resolution, and large length span is demostrated.

❖2 µV/µm spatial resolution is an order higher than analogous polymer based PSD structure and the position resolution is comparable to commercial PSDs

Chapter 4

Page 31

Ashar, Ganesh and Narayan Adv. Elec. Mat. 2017

74

Experimental Setup

75

Results from the photocurrent scanning along with transmittance of two different devices.Variations in the photocurrent response (indicated by color contrast)

76Ingress of moisture and oxygen happens from the periphery

(a)

(b)

77

D1

D2

D3

D4

D5

D6

D7

1 2 3 4

2-D photocurrent scanning for 4 𝑚𝑚 × 4 𝑚𝑚 area with a beam size of ~10 µm and intensity 1mW/cm2.The regions of different photocurrent can be seen with the color contrast. Figure shows device degradation with time.

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Apoorva Singh, Suman Banerjee, Pabitra Nayak, Zhipping Wang, Jacob Wang H.J. Snaith and K.S. Narayan, Insights in tothe microscopic and degradation processes in hybrid perovskite solar cells using noise spectroscopy and photocurrent

scanning (Solar RRL 2017)

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➢ Perovskite-based solar cells exhibit characteristic noise features.

➢ The magnitude of the fluctuations and the associated PSD response directly correlates to the state of the device.

➢ Devices with inverted structure were found to be most stable against the illumination in the present studies.

➢ Noise measurements along with a suitable model appear to be a valuable tool to evaluate the defect characteristics.

➢ These studies are useful and relevant in gauging the feasibility of hybrid perovskite-based cells.

Th. B.SinghA.G.ManojDinesh KabraDhritamn GMonojit BagSabyasachi M.Anshuman DSatyaprasadRavichandranV. VijayPrashanthVini GautamRishav HarshKishore C

Prashant KSwatiRaageshAsharAnaranya

GaneshApoorva SinghSuman BAbdul

Funding: JC Bose Fellowship Grant, Indo-UK APEX

Anil KumarSridhar RajaramSatish PatilSanjio ZadeParameswaran IyerT.G.RajuAsha ShyamaJames DurrantA. FachettiT. Marks

Henry SnaithR. H. FriendSuby GeorgeSatish Ogale

techniques to study degradation in pvs · major kinds of degradation in perovskite solar cells...

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