innovative characterization of amorphous and thin …...innovative characterization of amorphous and...

Innovative Characterization of Amorphous and Thin-Film Silicon for Improved Module Performance

1Department of Physics and Material Science Institute

J. David CohenDepartment of Physics and Materials Science Institute University of Oregon, Eugene, OR 97403

Support the development of two thin-film technologies

Relevance/Objective

1. Thin Film Silicon-Based Devices• Characterize the electronic properties of nanocrystalline silicon to

help optimize for bottom cell component in multijuction cells.

• Aid in developing better high deposition rate materials, particularly the amorphous silicon-germanium alloys

• Understand mechanisms of light-induced degradation

2. Copper Indium Di-Selenide Based Devices• Identify factors limiting performance of commercial devices

relative to high performance laboratory cells

Summary of Activities

1. Evaluate the effects of oxygen contamination on the electronic properties of high quality NREL hot-wire CVD amorphous silicon-germanium alloys

2. Examine the electronic properties of United Solar nanocrystalline silicon, their relationship with cell performance, and their light-induced degradation.

3. Examine correlations between the electronic properties of high performance NREL CIGS materials and associated cell performance.*

* Not to be included in this presentation due to lack of time

A. Technical Focus of Recent Activities

Activities: Participants

B. Participants in Recent Activities University of Oregon Personnel:Name Primary Activity in Current PeriodJ. David Cohen Program ManagerShouvik DattaResearch Associate

Studies of NREL HWCVD amorphous silicon-germanium alloys

Peter HuggerResearch Assistant

Evaluation of USOC nanocrystalline silicon materials

Pete ErslevResearch Assistant (part-time)

Electronic properties of Cu(In,Ga)Se2materials in NREL laboratory cells

Thin-Film Partnership Collaborators:

Organization Primary Personnel InvolvedNREL Yueqin Xu, A.H. Mahan, Howard Branz,

Miguel Contreras, Rommel NoufiUnited Solar Ovonic Baojie Yan, Jeffrey Yang, Subhendu Guha

C. Experimental Methods Employed

I. Transient Photocapacitance SpectroscopyA type of sub-band-gap optical absorption spectroscopy

Discloses: Band-tail distributions, deep defect distributions and properties, minority carrier transport

II. Admittance/Drive-level capacitance profilingDiscloses: Majority carrier density, majority carrier mobility,

deep defect densities and their capture cross sections

Activities: Methods

Comparison of Sub-band-gap Optical Spectroscopies

Method Detected Quantity DisadvantagesDirect Transmitted/Reflected Light Not Sensitive enough for thin films

Photothermal Deflection (PDS)

Absorbed Energy Dominated by surface defects for low bulk defect samples

Constant Photo-current Method(CPM)

Carriers Photoexcited into Majority Band

Carrier mobility influences spectra; Dominant current path may not reflect internal bulk properties

Photoemission Electrons ejected into vacuum Very surface sensitive

PhotocapacitanceSpectroscopy

Photoexcited released charge from depletion region

Requires reasonably good barrier junction, moderate conductivities

This last method is thus naturally suited for examining sub-band-gap optically induced defect transitions within photovoltaic devices.

Activities: Methods

Photocapacitance Spectra for Disordered Semiconductors

Two Primary Features:

(1) Exponential “Urbach” Tail.g(E) ∝ exp(E/EU) where EU

indicates degree of disorder

(2) Dominant Deep defect band.Usually well fit to a Gaussiandistribution of transitions

EU=42meV

Intrinsic a-Si:H

Gelatos, Mahavadi, Cohen, and Harbison, Appl. Phys. Lett (1988)

Activities: Methods

Drive level capacitance profiling (DLCP)Michelson, Gelatos, and Cohen, Appl. Phys. Lett. 47, 412 (1985).

•Junction capacitance is determined as a function of the frequency and the amplitude ofthe applied oscillatory voltage.

•One obtains a direct integral over defect states down to an emission cutoff energy, Ee:

•Procedure is then repeated at different dc biasto produce spatial profile.

C = C0+C1δV+C2δV2+…

∫−

+=−=F

eC

E

EEDL dxxEgn

CAqCN ),(

2 12

30

ε

Ee = kBT log(ν/ω)

Activities: Methods

Schematic showing portion of the defect band that is detected by the drive-level profiling method (shaded region). Ndl corresponds to an integral over g(E):

where Ee = kBT ln(ν/ω)

Drive-level Profiles for Amorphous Silicon Sample

∫∫−−

≈+=−=F

eC

F

eC

E

EE

E

EEDL dxxEgdxxEgn

CAqC

N ),(),(2 1

2

30

ε

We infer a broad deep defect about 0.8eV below EC of density ~ 1.5 x 1016 cm-3

Activities: Methods

Budget History

ProjectTask(s)

Total Value

High growth rate a-Si,Ge:H alloys

Nanocrystalline Si films and devices

CIGS electronic properties vs. devices

Grand Total over 16 months

40%(~$90K)

40%(~$90K)

20%(~$40K)

~$220K

Expenditures: October 2005 to January 2007

(1) HWCVD Amorphous Silicon-Germanium Alloys

• Background: Need for higher deposition rate a-Si,Ge:H material

• Improved Hot-Wire CVD Deposited a-Si,Ge:H seems promising

With Yueqin Xu, Harv Mahan, and Howard Branz

Accomplishments

• Loss of Optimum Properties Due to Oxygen Contamination?

• Results on 2006 Sample Series with Controlled Oxygen Leak

Critical Need: a-SiGe:H Cells at Higher Growth Rates

• United Solar devices – All in Light Degraded State

• Specular Stainless Steel -- No back reflector

Accomplishments: Background

Electronic Properties of High Growth Rate Materials

Cell performance deteriorates as growth rate is increased, and this appears to be uncorrelated with deep defect densities

Higher Urbach energies (bandtail widths) appear to be strongly correlated with higher growth rates and poorer cell performance

Higher frequencies for PECVD growth yield higher performance (and narrower bandtails). Not as successful for a-Si,Ge:H.

Possible solution explored at NREL: Hot-wire CVD of a-Si,Ge:H


Urbach Energies for the Best PECVD a-SiGe:H


The Best PECVD vs. HWCVD a-Si,Ge:H


Spectra for NREL HWCVD a-Si,Ge:H

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Photon energy (eV)

10-142

10-132

10-122

10-112

10-102

10-9

Phot

ocap

acita

nce

sign

al (a

rb. u

nits

)

0at.% Ge5at. % Ge20at. % Ge

55meV

45meV45meV

SS substrates

2000oC Tungsten Filament

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.01x10-14

1x10-13

1x10-12

1x10-11

1x10-10

1x10-9

15at.% Ge 29at.% Ge 47at.% Ge

Phot

ocap

acita

nce s

igna

l (ar

b.un

its)

Photon Energy (eV)

1800oC Tantalum Filament

42meV43meV

45meV


The Best PECVD vs. HWCVD a-Si,Ge:H


2005 Samples Exhibited Poorer Properties

0.50 0.75 1.00 1.25 1.50 1.75 2.0010-7

10-6

1x10-5

1x10-4

10-3

10-2

10-1

100

101

29% Ge,More O2,E

U~66 meV

29% Ge,Less O2,EU~43 meV

Phot

ocap

acita

nce

Sign

al (a

rb.u

nits

)

Energy (eV)

Photocapacitance Spectra: 29at.% Ge

10 15

10 16

1017

1018

10 19

10 20

1021

10 22

2.01.51.00.50.0

Depth: [µm]

L1306_O_level L1430_O_level

Oxygen SIMS Profiles

43meV

66meV


Oxygen Contamination Problem Resolved

Controlled leak valve added

New sample series deposited by Yueqin Xu in early 2006 with varying air leak contamination levels

Fall 2005: Leak source identified and eliminated

0.50 0.75 1.00 1.25 1.50 1.75 2.0010-7

10-6

1x10-5

1x10-4

10-3

10-2

10-1

100

101

29% Ge,More O2,E

U~66 meV

29% Ge,Less O2,EU~43 meV

Phot

ocap

acita

nce

Sign

al (a

rb.u

nits

)

Energy (eV)

Photocapacitance Spectra: 29at.% Ge

43meV

66meV

Accomplishments

HWCVD a-Si,Ge:H Sample Series with Controlled Air Leak

SIMS Analysis:

Germanium content 29-32at.% for all samples

Systematic oxygen level variation

Sample Air leak Flow rate (sccm)

Oxygen Content ( cm-3)

Thickness (μm)

Initial Substrate Temp (K)

Final Substrate

Temp (K)

Gas Ratio

GeH4/(GeH4+SiH4)

A 0.00 ~8×1018 1.80 204 289 0.19 B 0.02 ~3×1019 1.60 204 289 0.19 C 0.06 ~1×1020 1.75 204 284 0.19 D 0.20 ~5×1020 2.20 204 275 0.19

(oC)(oC)

0.01 0.1

1019

1020

Accomplishments

0.1

1

Rat

io o

f 74G

e/30

Si (a

rb.u

nits

)

Oxy

gen

Con

tent

(cm

-3)

Air leak Flow Rate (sccm)

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.810-15

1x10-14

1x10-13

1x10-12

1x10-11

1x10-10

1x10-9

1x10-8

350 K1.1 kHz

TPC

(arb

.uni

ts)

Incident Photon Energy (eV)

A, 0.00 sccm C, 0.06 sccm D, 0.20 sccm

Photocapacitance Spectra for Oxygen Series

Sample A exhibits EU = 43.5meV

Sample B exhibits EU = 38 meV (?)

Does this mean low levels of oxygen actually improves the electronic properties of HWCVD a-SiGe:H materials?

(NO, but it doesn’t hurt that much either)

Accomplishments

Defect Densities from DLCP Measurements

Mid-gap defect densities are low and vary roughly by a factor of two over range of oxygen

Larger density in higher leak samples may be due to effects of oxygen weak donor level

0.3 0.4 0.5 0.6 0.71015

1016

1017

Accomplishments

A B C D

ND

L (cm

-3)

Distance from the Barrier (μm)

State B

0.00 sccm0.02 sccm0.06 sccm0.20 sccm

Light-Degraded State

Sensitivity to Minority Carrier Collection

• If both escape depletion region there is no net change in charge density

⇒ Small photocapacitance signal, but larger junction photocurrent signal

EF

EC

EV

Photocapacitance signal ∝ n - p while Photocurrent signal ∝ n + p

• For optical energies near the gap, electrons and holes generated equally

Accomplishments

Measuring Fraction of Collected Holes in a-Si,Ge:H

United Solar RF35at.% Ge

Compare transient photocapacitance and photocurrent spectra

Ratio of signals in bandtail region⇒ the hole collection fraction is ≈ 95%

under our experimental conditions

(c) (d) (a) (b)

EC

EF

EV

Toward Barrier Junction

(a) (b)(c) (d)

Ratio is nearly a constant:

(1+p/n)/(1-p/n)

Accomplishments

Measuring Fraction of Collected Holes

United Solar RF35at.% Ge

United Solar RF PECVD 35at.% Ge Sample

Hole Collection: 95% 66%

Accomplishments


Hole Collection: 98%

NREL Hot-Wire CVD 29at.% Ge, No air-leak

No air-leakState A

99%

No air-leakState B

Accomplishments


Hole Collection: 95%

NREL Hot-Wire CVD 29at.% Ge, 0.06sccm air-leak

0.06 sccmair-leakState A

97%

0.06 sccmair-leakState B

Accomplishments

Effect of Extra Oxygen: New Defect Transition

NREL Hot-Wire CVD 29at.% Ge, 0.06sccm air-leak

0.06 sccmair-leakState BIntroducing this defect transition (in addition

to usual mid-gap deep defect) allows excellent fits to both TPC and TPI (thin lines shown)

Urbach is actually 47meV, not the < 40meV value that seemed to fit TPC by itself

Moderate oxygen levels do not appear to greatly impair hole collection, or the sus-ceptibility to light-induced degradation

Dip in TPC Spectrum is due to a 1.4eV transition from VB into empty defect level

Accomplishments

HWCVD a-Si,Ge:H Summary

Bad News: Oxygen wasn’t the problem, so we really don’t know why the samples produced during 2005 were so poor!

Good News: HWCVD a-Si,Ge:H Samples again exhibit excellent electronic properties! (in some respects, even betterthan the best PECVD samples)

Interesting: Oxygen introduces new defect transition into gap: The oxygen donor level predicted as long as 24 years ago?

Accomplishments

(2) Nanocrystalline Silicon Materials Properties

TPC Spectra reveal mixed phase nature of nanocrystalline SiTemperature variation shows degree of minority carrier collection

New Sample Series StudiedHigh efficiency working n-i-p devices examined directly

Hole Collection Determined via TPC vs. Device Performance Is there a correlation?

Nature of light-induced degradationPossible model is proposed

UNITED SOLAR OVONICwith Baojie Yan, Jeffrey Yang, and Subhendu Guha

Accomplishments

A.F. Halverson, J.J. Gutierrez, J.D. Cohen, B. Yan, J. Yang, and S. Guha, Appl. Phys. Lett. 88, 71920 (2006)

Comparing CPM and Photocapacitance Spectrum for nc-Si:H

FTPS w/o Si FilterFTPS w Si FilterCPM

Fourier-Transform Photo Current Spectroscopy(FTIR) and CPM Spectra

United Solar nanocrystalline Si spectrum from TPC spectroscopy


M. Vaněček, A. Poruba, Z. Remeš, N. Beck, and M.Nesládek, J. Non-Cryst. Solids 227-230, 967 (1998).

Very temperature dependent !

EC

EV

EF

Junction Interface

In a-Si:H component many holes remain trapped ⇒ mostly electrons escape ⇒ large photocapacitance signal

Electron Energy

a-Si:H

nanocrystallites

y

At photon energies greater than 1.1eV, free electronsand holes excited in nano-crystallites.

At moderately high temper-atures both carriers escape⇒ little change in charge⇒ small photocapacitance signal

x

Hole Collection Inhibited in a-Si:H Component


Minority Carrier Collection Increases with T

0.8 1.0 1.2 1.4 1.6 1.8 2.0

Incident Light Energy (eV)

1015

1016

1017

1018

1019

1020

1021

1022

Pho

toca

paci

tanc

e si

gnal

(a.u

.)

170K300K

(a) USOC 14661State A

Transient Photocapacitance

0.8 1.0 1.2 1.4 1.6 1.8 2.0

Incident Light Energy (eV)

1015

1016

1017

1018

1019

1020

1021

1022

1023

Pho

tocu

rren

t Sig

nal (

a.u.

)

170K300K

(b) USOC 14661State A

Transient Junction Photocurrent

Photocurrent signal dominated by nanocrystallite component at all T

Increased minority carrer collection suppresses signal in nanocrystallites


Types of Nanocrystalline Si Devices StudiedDeposited at : United Solar Ovonic Corp.

SANDWICHSS/n+/a-Si:H/nc-Si:H/a-Si:H

Advantages:- Purely intrinsic layers- Blocks diffusion of O2

Disadvantages:- Contains a-Si:H layers- Differs from working device

~1.3 μm .7 μm

Advantages:- Purely nc-Si:H- Working device allows compar-

ison with cell peformanceDisadvantages:

- Contains thin p+ and n+ layers

n-i-pSS/n+/i/p+/TCO

~1.1 μm

Most sample devices examined prior to Fall, 2005.

Sample devices studied since late 2005


Sample No Substrate Jsc Voc FF Eff (%) H2 Dilution

14027 Ag/ZnO 26.5 0.469 0.581 7.22 Ramping14036 SS 17.38 0.448 0.568 4.42 Ramping14037 Ag/ZnO 25.99 0.429 0.512 5.71 Constant14038 SS 17.36 0.451 0.531 4.16 Constant13993 Ag/ZnO 24.39 0.548 0.641 8.57 Ramping

Early 2006 United Solar nc-Si:H Device Series

All are n-i-p devices with either Specular Stainless (SS) substrates, or with textured Ag/ZnO back reflectors. All i-layers were more than 1 micron thick.

Samples were deposited either using a constant level of hydrogen dilution, or with a linear ramp variation in hydrogen dilution to control crystallite size

Final sample in list is close to the current best nc-Si:H United Solar device

Accomplishments

Crystalline Fractions Revealed by Raman Spectroscopy

300 400 500 600

300 400 500 600

Raman Shift (cm-1)

USOC 1399353vol.%

USOC 1403663vol.%

780n

m R

aman

Sig

nal

Low crystalline fractions yield highest VOC’s

No clear correlations for fractions above 60vol.%

Accomplishments

DLC Profiles for Constant vs. Ramped H-dilution

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

1E15

1E16

1E17 USOC RF14036DLCP 1.1kHz

375K 350K 325K 300K

Driv

e Le

vel D

ensi

ty (c

m-3

)

Profile Distance <x> (μm)0.1 0.2 0.3 0.4 0.5 0.6 0.7

1E15

1E16

1E17USOC RF14038DLCP 1.1kHz

350K 325K 300K 275K 250K

Profile Distance <x> (μm)

Constant H-dilution Linearly Ramped H-dilution

Consequences of employing varying H-dilution to limit crystallite size:

Large defect density near n-i junction can be decreasedLower defect density maintained through most of bulk film region

Accomplishments

Spectra for 8.57% Textured n-i-p Device

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

TPI TPC, 285K

USOC RF13993

Pho

totra

nsie

nt S

igna

l (a.

u.)


Here an a-Si:H componentis clearly in evidence

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

TPI TPC, 275K TPC, 285K

USOC RF13993

Pho

totra

nsie

nt S

igna

l (a.

u.)


Reducing the temperature increases nanocrystallite signal

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

TPI TPC, 275K TPC, 285K TPC, 295K TPC<0

USOC RF13993

Pho

totra

nsie

nt S

igna

l (a.

u.)


Increasing the temperatureactually yields a negativeTPC signal near 1.5eV !

Accomplishments

Temperature Dependence of Hole Collection in nc-Si:H

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

TPC, 285K TPC, 275K TPC, 295K TPC<0

USOC RF13993

Pho

totra

nsie

nt S

igna

l (a.

u.)


Two activated hole trap processes seem to be evident in this sample

3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0103

104

105

106

TPC spectra from 8.57% n-i-p sample device

signal>0 signal<0

USOC RF13993

Ea=.15 eV

Ea=.72 eV

TP

C S

igna

l

1000/T (K-1 )

Increasing hole collection

Accomplishments

Comparison of the three Ag/ZnO Devices plus one from previous sample series

Correlation with Cell Performance

Accomplishments

Minority carrier collection determined from TPI/TPC ratio at 300K near 1.5eV

Correlation looks promising, but data from more sample devices need to be added

Effects of Prolonged Light Exposure

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

TPC, 285K TPC, 275K TPC, 295K TPC<0

USOC RF13993

Pho

totra

nsie

nt S

igna

l (a.

u.)


Effect of varying temperature

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2102

103

104

105

106

107

State B State A

USOC RF13993295 K

Pho

toca

paci

tanc

e S

igna

l (a.

u.)


Annealed vs. light-soaked state

50 hours of light- soaking of 610nm filtered ELH light at 500mW/cm2

Accomplishments

Effect of Light Soaking on TPC Spectra

Light-soaking significantly reduces hole collection

Effect of Light Soaking on Capacitance Profiles

a)

USOC RF14036

350 K325 K300 K

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

1E15

USOCRF14036State B

350 K325 K300 K

Distance FromJunction Interface (μm)

b)

Accomplishments

Does light soaking actually reduce the density of deep defects?

No, we believe it increases the an activation barrier that inhibits its response

Annealed State Light-soaked State

Proposed Model to Explain Changes with Light-Soaking

Accomplishments

E F E F

As illustrated, positive charge collects at the a-Si:H/crystallite interfaces, while compensated by negative charge in the a-Si:H region, and the crystallites nearby.

Holes have larger potential barriers at the phase boundary. Also, the activation energy for exchanging electrons between deep defects and conduction band increases.

In light-soaked State B, defects shift down in energy with respect to the bulk conduction band.

Major Events/Milestones

Key Findings and Conclusions

Our measurements continue to show superior electronic properties for lower filament temperature NREL HWCVD a-Si,Ge:H alloys.

The minority hole collection appears nearly as good as the best PECVD alloys with possibly less deterioration after light soaking.

Previous problems with air contamination were solved; moreover, a distinct oxygen related defect state has been identified.

We have successfully carried out TPC and TPI sub-band-gap spectroscopy on nc-Si:H n-i-p devices employing both SS and textured Ag/ZnO substrates.

A correlation appears to exist between the minority carrier collection fraction deduced by the TPC measurements and the device performance.

Light-induced degradation exists and reduces minority carrier collection. A possible mechanism to explain our observations has been formulated.

Future Directions

Broad Future Plans

NREL HWCVD a-Si,Ge:H

Work with NREL as they seek to incorporate and optimize performance of their HWCVD a-Si,Ge:H materials within photovoltaic devices.

Evaluate the electronic properites of NREL HWCVD a-Si,Ge:H under higher deposition rates (greater than the ~2Å/s materials studied to date)

Examine alloys with other Ge fractions, and determine whether the effects of oxygen contamination appear similar.

United Solar nanocrystalline Si

Examine properties of nc-Si:H closer to a-Si:H transition region to help understand how far one can go toward maximizing VOC without reducing JSC

Explore the effects of hydrogen profiling over a greater range of parameter space

Test the implications of proposed light-induced degradation model; for example, by varying photon energies, or examining such effects under applied bias.

THANK YOU!

Studies of NREL Fabricated CIGS Devices using Admittance Spectroscopy and DLCP

Accomplishments

Eight NREL Devices from Three Depositions

Device#

VOC(volts)

JSC(mA/cm2

)

Fill Factor (%)

Efficiency(%)

C1919-11 Cell 3 0.630 32.95 71.43 14.833C1919-11 Cell 4 0.642 32.51 68.99 14.393C1813-21 Cell 3 0.657 33.26 76.08 16.613C1813-21 Cell 4 0.664 32.67 77.82 16.888C1813-21 Cell 6 0.667 33.19 77.52 17.168C1924-1 Cell 4 0.724 30.82 78.19 17.449C1924-1 Cell 5 0.717 30.81 77.44 17.118C1924-1 Cell 6 0.714 30.95 77.07 17.039

Sample devices provided by Miguel ContrerasThree depositions: Each such sample contained 6 devices8 devices with varying levels of performance were chosen for studyDevice areas were 0.406 cm2 in all cases

Accomplishments

Eight NREL Devices from Three DepositionsRelationship of VOC×JSC products and Fill Factors to Device Efficiencies

: C1919 devices, : C1813 devices, and : C1924 devices

Fill factor variations account for most of the differences in efficiencies

• The C1924 devices differ somewhat from the C1919 and C1813 devices, exhibiting higher VOC’s and lower JSC’s.

• The C1924 devices have a slightly higher Ga fraction.

Accomplishments

SIMS Analysis: Ga to In Ratios

0 400 800 1200

0

2

4

6

NREL Samples 1924, 1813, and 1911TOF-SIMS Depth Profi le AnalysisScaled Time on 1924

^71

Ga

/ ^11

3 In

T ime (s)

Sample 1924 Sample 1813 Sample 1911

Depositions for samples 1813 and 1911 have nearly identical composition profiles, while deposition for sample 1924 is significantly different.

Accomplishments

Zero-Field RegionDLCP Density

Depletion RegionDLCP Density

2) NREL C1919 Cell 4: 14.4%

0. 2 0 .3 0.4 0 .5 0 .6 0. 73

1 E1 6

Comparison of DLC Profiles

N R EL C 1 91 9 -1 1 C el l 4, 1 4.4 % ef f .D L C P 10 k H z 0 8 -2 3- 20 0 5A re a = .40 8 c m 2

NDL

(cm

-3)

P ro fi le D e pth ( μm )

8 0 K 1 2 0 K 1 6 0 K 2 0 0 K

0. 2 0 .3 0 .4 0 .5 0 .6 0.7

3

1 E 1 6

N R E L C 1 92 4 -1 C e ll 4 , 1 7 .4 % e ff .D L C P 10 k H z 0 8- 2 1- 20 0 5Ar e a = .40 8 c m 2

NDL

(cm

-3)


8 0 K 1 2 0 K 1 8 0 K 2 0 0 K

4) NREL C1924 Cell 4: 17.4%

0. 1 0. 2 0. 3 0. 4 0. 5 0.6 0.7 0.8 0.9 1.01 E1 5

3

1 E1 6N R E L C 18 1 3- 21 C e ll 4 , 16 .9% e f f .D LC P 1 0 k H z 08 - 28 -2 0 05A r ea = .4 1 0 c m 2

NDL

(cm

-3)


8 0 K 1 2 0 K 1 6 0 K 2 0 0 K

3) NREL C1813 Cell 4: 16.9%

Accomplishments

Correlation of Device Efficiencies with DLCP Densities in Different Absorber Regions

DLCP Densities in Region Close to Barrier DLCP Densities in Zero-Field Region

Correlation of efficiencies to DLCP density close to barrier is quite good, except for the 3 high VOC devices from sample C1924-1For those 3 devices we believe the higher value of VOC is due to a slightly higher Ga fraction, and because the carrier density is higher outside the depletion region.

Accomplishments

innovative characterization of amorphous and thin …...innovative characterization of amorphous and...

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