The document summarizes research on understanding the physics of degradation in polymer solar cells. Key points include:
1) Polymer solar cells suffer from various degradation factors like oxygen, moisture, and light exposure that reduce efficiency over time.
2) Experiments showed degradation under light exposure in inert atmospheres, with blue photons found to be particularly detrimental. Increased sub-band gap states and reduced mobility were observed.
3) Post-degradation thermal annealing was able to partially recover performance by reducing sub-band gap states, suggesting the active layer was under-annealed initially.
Loss mechanisms in Polymer-Fullerene Solar Cellsdisorderedmatter
A combination of transient photovoltage (TPV), voltage dependent charge extraction (CE) and time delayed collection field (TDCF) measurements is applied to poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5-b’]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]- phenyl-C71-butyric acid (PC71BM) bulk heterojunction solar cells to analyze the limitations of photovoltaic performance. Devices are processed from pure chlorobenzene (CB) solution and a subset was optimized with 1,8-diiodooctane (DIO) as co-solvent. The dramatic changes in device performance are discussed with respect to the dominating loss processes. While in the devices processed from CB solution, severe geminate and nongem- inate recombination is observed, the use of DIO facilitates efficient polaron pair dissociation and minimizes geminate recombination. Thus, from the determined charge carrier decay rate under open circuit conditions and the voltage dependent charge carrier densities n(V), the nongeminate loss current jloss of the samples with DIO alone enables us to reconstruct the current/voltage (j/V) characteristics across the whole operational voltage range. Geminate and nongeminate losses are considered to describe the j/V response of cells prepared without additive, but lead to a clearly overestimated device performance. We attribute the deviation between measured and reconstructed j/V characteristics to trapped charges in isolated domains of pure fullerene phases.
Acceptor–donor–acceptor small molecules based on derivatives of 3,4-ethylened...Boniface Y. Antwi
Simple EDOT based photo-active molecules have been synthesised by fewer synthetic steps. The molecules separately acted as donor units in organic solar cells fabrications. Best device efficiency was 1.36%.
Loss mechanisms in Polymer-Fullerene Solar Cellsdisorderedmatter
A combination of transient photovoltage (TPV), voltage dependent charge extraction (CE) and time delayed collection field (TDCF) measurements is applied to poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5-b’]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]- phenyl-C71-butyric acid (PC71BM) bulk heterojunction solar cells to analyze the limitations of photovoltaic performance. Devices are processed from pure chlorobenzene (CB) solution and a subset was optimized with 1,8-diiodooctane (DIO) as co-solvent. The dramatic changes in device performance are discussed with respect to the dominating loss processes. While in the devices processed from CB solution, severe geminate and nongem- inate recombination is observed, the use of DIO facilitates efficient polaron pair dissociation and minimizes geminate recombination. Thus, from the determined charge carrier decay rate under open circuit conditions and the voltage dependent charge carrier densities n(V), the nongeminate loss current jloss of the samples with DIO alone enables us to reconstruct the current/voltage (j/V) characteristics across the whole operational voltage range. Geminate and nongeminate losses are considered to describe the j/V response of cells prepared without additive, but lead to a clearly overestimated device performance. We attribute the deviation between measured and reconstructed j/V characteristics to trapped charges in isolated domains of pure fullerene phases.
Acceptor–donor–acceptor small molecules based on derivatives of 3,4-ethylened...Boniface Y. Antwi
Simple EDOT based photo-active molecules have been synthesised by fewer synthetic steps. The molecules separately acted as donor units in organic solar cells fabrications. Best device efficiency was 1.36%.
Current Status of Solar Photovoltaic Technology Platforms, Manufacturing Issu...Tuong Do
Speaker: Dr. Steven S. Hegedus, Institute of Energy Conversion, University of Delaware
In his talk, Dr. Hegedus, a 30-year solar cell research veteran, provides an overview of the existing status of today's solar technology platforms and manufacturing issues, as well as provide viewers with his perspective looking 3 to 5 years into the future. He discusses cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) thin-film technology. He also provides up-to-date results for advanced crystalline silicon (c-Si) high efficiency cell technology concepts such as the amorphous/c-Si heterojunction, all-back-contact cells, selective emitters and laser-fired contacts. Finally, he briefly describes his lab's current work on addressing critical issues in CIGS and c-Si cell technology.
Dr. Hegedus has been a member of the research staff at IEC at the University of Delaware, the world's oldest photovoltaic research laboratory, since 1982. He co-edited the 1st and 2nd editions of the "Handbook of Photovoltaic Science and Engineering" (Wiley 2003, 2011) and is a co-editor of the journal "Progress in Photovoltaics."
Thursday, Sept. 27, 1 p.m. EDT
Source: http://www.photonics.com/Webinar.aspx?WebinarID=24
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Current Status of Solar Photovoltaic Technology Platforms, Manufacturing Issu...Tuong Do
Speaker: Dr. Steven S. Hegedus, Institute of Energy Conversion, University of Delaware
In his talk, Dr. Hegedus, a 30-year solar cell research veteran, provides an overview of the existing status of today's solar technology platforms and manufacturing issues, as well as provide viewers with his perspective looking 3 to 5 years into the future. He discusses cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) thin-film technology. He also provides up-to-date results for advanced crystalline silicon (c-Si) high efficiency cell technology concepts such as the amorphous/c-Si heterojunction, all-back-contact cells, selective emitters and laser-fired contacts. Finally, he briefly describes his lab's current work on addressing critical issues in CIGS and c-Si cell technology.
Dr. Hegedus has been a member of the research staff at IEC at the University of Delaware, the world's oldest photovoltaic research laboratory, since 1982. He co-edited the 1st and 2nd editions of the "Handbook of Photovoltaic Science and Engineering" (Wiley 2003, 2011) and is a co-editor of the journal "Progress in Photovoltaics."
Thursday, Sept. 27, 1 p.m. EDT
Source: http://www.photonics.com/Webinar.aspx?WebinarID=24
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Nanotechnology is the nexus of sciences.
It includes anything smaller than 100 nanometers with novel properties.
The conventional solar cells that are used to harness solar energy are less efficient and cannot function properly on a cloudy day.
The use of nanotechnology in the solar cells created an opportunity to overcome this problem , thereby increasing the efficiency.
An Experimental Study of P&O MPPT Control for Photovoltaic SystemsIJPEDS-IAES
Tracking the maximum power point plays an important role for the optimization of the solar energy. The objective here is to study experimentally optimizing photovoltaic (PV) systems connected to a DC-DC converter (Boost) and a resistive load. For this, tests were conducted to determine the law of open loop control (power versus the duty cycle) for different solar irradiance values and load with an approximately constant cell temperature. The obtained results showed that the power passes through a maximum point. In order to extract the maximum power, for different values of solar irradiance and load, an MPPT control "Perturb and Observe" P & O has been implemented on a DSPACE 1104. The experimental results showed the performance of the method suggested.
A NOVEL APPROACH TO OBTAIN MAXIMUM POWER OUTPUT FROM SOLAR PANEL USING PSOijsrd.com
The configuration of a most extreme force point following (MPPT) controller for a sun based photovoltaic force framework is proposed using a help converter topology utilizing PSO calculation. Sunlight based board voltage and current are consistently checked by a shut circle focused around PSO microcontroller control framework, and the obligation cycle of the help converter persistently changed in accordance with concentrate greatest force. Framework testing affirms crest force following under changing lighting conditions. Under particular conditions, efficiencies in overabundance of 96% are demonstrated to be conceivable.
Горбунов Н.А., Государственная морская академия им. С.О. Макарова, г. Санкт-Петербург
Разработка плазменных технологий для прямого фотоэлектрического преобразования с сфокусированного солнечного излучения
Investigations on Capacitor Compensation Topologies Effects of Different Indu...IJPEDS-IAES
This paper presents investigations on capacitor compensation topologies with
different inductive coupling links for loosely coupled inductive power
transfer (IPT) system. In general, the main constraint of the loosely coupled
IPT system is power losses due to the large leakage inductances. Therefore,
to overcome the aforementioned problem, in this work, capacitor
compensation is proposed to be used by adding an external capacitor to the
system. By using this approach, the resonant inductive coupling can be
achieved efficiently and hence the efficiency of the system is also increased
significantly. This paper analyzes the performance of two different
compensation topologies, which are primary series-secondary series (SS) and
primary series- secondary parallel (SP) topology. The performance of such
topologies is evaluated through the experimental results at 1MHz operating
frequency for different types of inductive coupling. From the results, SS
topology produces a high power transfer but SP topology gives better
efficiency.
Simulation study of single event effects sensitivity on commercial power MOSF...journalBEEI
High-frequency semiconductor devices are key components for advanced power electronic system that require fast switching speed. Power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is the most famous electronic device that are used in much power electronic system. However, the application such as space borne, military and communication system needs Power MOSFET to withstand in radiation environments. This is very challenging for the engineer to develop a device that continuously operated without changing its electrical behavior due to radiation. Therefore, the main objective of this study is to investigate the Single Event Effect (SEE) sensitivity by using Heavy Ion Radiation on the commercial Power MOSFET. A simulation study using Sentaurus Synopsys TCAD software for process simulation and device simulation was done. The simulation results reveal that single heavy ion radiation has affected the device structure and fluctuate the I-V characteristic of commercial Power MOSFET.
Seminar slides presenting work on dark matter annihilation into light mediators which subsequently decay in to Standard Model particles. This is motivated by indirect detection signals in gamma rays, such as the recent excess seen in the Fermi Large Area Telescope.
1. Understanding the physics of
degradation of polymer solar cell.
Joydeep Bhattacharya
Final Oral –PhD
29th July , 2013
Dr Rana Biswas & Dr Vikram Dalal
The work is supported by
National Science Foundation & Iowa Power Fund
2. 2
DISCUSSION ON PHOTONIC BACK REFLECTOR
INTRODUCTION TO PLASTIC SOLAR CELLS
DIFFERENT DEGRADATION & THEIR SIGNATURE
INITIAL RESULTS
MORE RESULTS
PERFORMANCE RECOVERY
PHOTO STABLE ZNO:AL BASED OPV
CONCLUSION
OUTLINE
3. 3
Introduction
Energy Requirement of Entire Earth- 1.99 TW only 0.02 % of the total solar
radiation that reaches Earth Surface ( 1.05E5 TW).
Market Share, Cost of the Module and status
Single Junction OPV can reach
7.2% while double junction
had achieved ~10.5% ( in lab)
International Energy Agency (IEA Report)2012
4. 4
Increase efficiency
Reduce costs
Improve stability
Some basic objective to reach-
Bandgap engineering, Introducing
Photonic –plasmonic architechture, New
architecture –super lattice,tandem
Addressed by roll to roll
fabricatioma/Use of Thinner
active layer
Better encapsulation from
environment
8. 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-0.5 -0.3 -0.1 0.1 0.3 0.5
Current(mA)
Voltage(Volt)
Pristine
After 56 Hrs
After 96 Hrs
8
SOLAR CELL STORRED IN AIR UNDER DARK CONDITION
The process is irreversible in nature
ROLE OF MOISTURE
Yue et al SOLMAT-2012/Kawano et al 2008-SOLMAT
10. 10
ROLE OF LIGHT
DEVICE PERFORMANCE CAN BE AFFECTED BY DIFFERENT
MECHENISM
1. Sub-band gap states creating recombination center due to photo oxidation.( This can be
initiated by even a trace amount of oxygen present in the active layer.
Craig H Peters et al. AFM 2012—McGeehe Group, Stanford
Absorbance(a.u)
Increase in sub band gap states shown by PDS
11. 11
ROLE OF LIGHT continued…
Ankit Kumar et al 2008 AFM, Yang Yang Group
Accumulation of space charge at D-A interface was held responsible
12. 12
ROLE OF LIGHT continued…
MO Reese et al 2010 AFM, NREL
Oxygen creates trap states in fullerene resulting in lower electron mobility
13. 13
RA Street et al 2013 APL & 2012-PRB, PARC
High energy photon can break C-H bond, and further theoretical studies show
that excess H can bind to other sites on the polymer creating localized
electronic states.
ROLE OF LIGHT continued…
14. 14
Oxygen held responsible for all photo degradation related
drop in OPV efficiency.
Under inert atmosphere- OPV are stable !!
MO Resse et al SOLMAT 2010/Krebs et al SOLMAT 2008
Summary
16. 16
Are polymer based cells stable under inert atmosphere and light?
If Unstable-What’s the reason of instability?
Which particular photon are harmful for OPV’s ?
What are the functional relationship between DOS and light intensity
Can we recover the loss of solar cell performances?
What could be the potential WAYOUT for photo-degradation?
Objectives..
18. 18
Can reach pressure to 1E-6 Torr with all optical & electrical systems inside
Degradation Chamber at Microelectronics Research Center
Such Low Pressure helps to eliminate the effect of moisture and oxygen
Except EQE all electrical measurement was done in-situ
ENVIRONMENTAL CHAMBER
24. Io Before – 9.7E-12 Amps
Io After – 4.5E-11 Amps
No change observed in calculated
Eu( Urbach Energy)
5 times
CHANGE IN DARK CURRENT & SUBGAP EQE
25. De-noised DOS DataC-f Raw Data
Indicating the presence of mid-gap states away from
valence band of P3HT (Polymer)
Mid-gap
States
Contribution to
capacitance
CHANGE IN DOS SPECTRA
26. 26
Need extra electric field for separation and collection.
Indicating a loss mechanism at interface
e
BIAS DEPENDENT CURRENT(WHY?)
27. EFFECT OF DIFFERENT WAVELENGTH EXPOSURE
Blue photon is detrimental to active layer photo degradation
34. 34
0 2 4
10
-11
10
-10
10
-9
Io( reverse saturation current ( low voltage regime)
n( ideality factor at low voltage regime)
Exposure Intensity(X-sun)
Io1(amps)
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
n1(idealityfactor)
0 2 4
1E-13
1E-12
1E-11
Io2( Higher voltage regime)
n2 ( Higher Voltage regime)
Io(amps
1.0
1.2
1.4
1.6
1.8
2.0
EXPOSURE INTENSITY(X- SUN)
n(Idealityfactor)
Change in Io1 & n at Low voltage region
35. 35
Change in Io2 & n2 at High voltage region
0 2 4
1E-13
1E-12
1E-11
Io2( Higher voltage regime)
n2 ( Higher Voltage regime)
Io(amps
1.0
1.2
1.4
1.6
1.8
2.0
EXPOSURE INTENSITY(X- SUN)
n(Idealityfactor)
Band-band recombination dynamics remains roughly same
36. 36
Prolonged light soaking creates excess mid-gap
recombination center facilitating SRH
recombination
“ UV PHOTON breaks C-H bonds, and that excess H can bind to other sites
on the polymer creating localized Electronic states” –Street et al- APL 2013
What we learnt?
44. STANDARD
CELL
INVERTED
CELL
PPA CONDITION-100 C -15 MIN INSIDE GB
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
Standard Cell
Cell With extended Annealing
PEDOT-ACTIVE LAYER-Ca(25 nm)/Al
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
VOLTAGE(VOLT)
CURRENT(ma)
PEDOT-ACTIVE LAYER-Ca(25 nm)/Al
PRISTINE
AFTER POST PROD ANNEALING
PPA
APPLIED
NO PPA,
EXTENDED
ANNEAL STEP
CHANGE IN Voc
TO SEE THE EXTRA EFFECT OF EXTENDED ANNEALING
( PPA)- EFFECT ON ACTIVE LAYER
45. STANDARD
CELL
INVERTED
CELL
PPA CONDITION-100 C -15 MIN INSIDE GB
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
PRISTINE
AFTER POST PROD ANNEALING
CURRENT(ma)
VOLTAGE(VOLT)
PEDOT-ACTIVE LAYER-Ca(25 nm)/Al
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
PRISTINE
AFTER POST PROD ANNEALING
CURRENT(ma)
VOLTAGE(VOLT)
PEDOT- ACTIVE LAYER -Al
NOTICED THIS?
( PPA)- EFFECT ON DIFFERENT CATHODE
46. STANDARD
CELL
INVERTED
CELL
PPA CONDITION-100 C -15 MIN INSIDE GB
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
VOLTAGE(VOLT)
CURRENT(ma)
Ca 10 nm
PRISTINE
AFTER POST PROD ANNEALING
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
CURRENT(ma)
VOLTAGE(VOLT)
PRISTINE
AFTER POST PROD ANNEALING
Ca 25 nm
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
VOLTAGE(VOLT)
CURRENT(ma)
PRISTINE
AFTER POST PROD ANNEALING
Ca 50 nm
ALMOST SAME DROP IN PERFORMANCES
( PPA)- EFFECT ON DIFFERENT ETL THICKNESS
47. STANDARD
CELL
INVERTED
CELL
PPA CONDITION-100 C -15 MIN INSIDE GB
-0.8 -0.4 0.0 0.4
0.0
0.5
1.0
1.5
Current(mA)
Voltage (volt)
Pristine
Post production annealing
10 nm MoOx
-0.8 -0.4 0.0 0.4
0.0
0.5
1.0
1.5
Voltage (volt)
Current(mA)
20 nm MoOx
Pristine
Post production annealing
-0.8 -0.4 0.0 0.4
0.0
0.5
1.0
1.5
Pristine
Post production annealing
Current(mA)
Voltage (volt)
30 nm MoOx
IDENTICAL DROP IN ALL THE THREE SAMPLES
( PPA)- EFFECT ON DIFFERENT HTL THICKNESS
48. STANDARD
CELL
INVERTED
CELL
PPA CONDITION-100 C -15 MIN INSIDE GB
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
1.6
Current(mA)
Voltage (volt)
Pristine
After PPA- 100C -15 min
Unannealed MoOx - 100 nm
-0.8 -0.4 0.0 0.4
0.0
0.4
0.8
1.2
1.6
Current(mA)
Voltage (volt)
Pristine
After PPA- 100C -15 min
Annealed MoOx - 100 nm -100C -10 min
( PPA)- EFFECT ON ANNEALED MoOx(HTL)
51. 51
0.3 0.4 0.5 0.6 0.7
1E16
1E17
1E18
PRISTINE
POST EXP-2X -48HRS
POST 1HR-110C ANNEAL
POST 1HR-90C ANNEAL
DOS(cm
-3
ev
-1
)
E-Ehomo
(ev)
Proof of Device active laye
being under annealed
This region of defects are not entirely reversible.
CHANGE IN DOS AFTER THERMAL ANNEAL
52. 52
CHANGE IN DOS WITH DIFFERENT ANNEALING TEMP
LOW FREQUENCY CV(24Hz)INTEGRATED FROM CF DATA
54. TCO
CHANGES
ARE MADE
IN TCO-
REST OF
THE
DEVICE
RECIPE
REMAINED
SAME
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8
0.0
0.5
1.0
1.5
Current(mA)
Voltage(Volt)
ZnO:Al
Cs2
Co3
on ZnO:Al
Cs2Co3 on ITO
ONLY ZNO:AL AS ETL
( DIFFERENT TCO- ITO OR ZNO)
55. TCO
Run No Time (Min) Rs ( Ω/□) Thickness(nm)
7964 20 6.44 1253
7965 15 10.05 933
7942 10.5 11.78 640
7967 5 43.67 312
MORE & MORE DROP IN BLUE PHOTON
TRANSMISSION AND DECREASE IN
SERIES RESISTANCE- WITH INCREASE IN
ZNO:AL THICKNESS
ZNO:AL FILM OPTIMIZATION
56. TCO
-0.8 -0.4 0.0 0.4
0.0
0.5
1.0
1.5
Current(mA)
Voltage (volt)
20 min
15 min
5 min
10.5 min
400 500 600 700 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
AbsEQE
Wavelength (nm)
20 min run -ZnO:Al
10 min run-ZnOLAl
5 min run-ZnO:Al
WITH INCREASE IN ZNO:AL THICKNESS
FF IMPROVES WITH DROP IN PHOTO CURRENT AT LOWER WAVELENGTH
CELL PERFORMANCES
57. TCO
0 500 1000 1500 2000
0.90
0.92
0.94
0.96
0.98
1.00
THICK ZNO-20 MIN
THIN ZNO -10 MIN
CONTROL -ITO
NORMALIZEDDROPINVoc
TIME IN MIN
0 500 1000 1500 2000
0.75
0.80
0.85
0.90
0.95
1.00
THICK ZNO-20 MIN
THIN ZNO -10 MIN
CONTROL -ITO
NORMALIZEDDROPINVoc
TIME IN MIN
Isc
THICKER ZNO:AL BASED DEVICE MORE PHOTO
STABLE WITH HIGHER EFFICIENCY
2X- PHOTO DEGRADATION
58. 58
CONCLUSIONS..
1. Photo degradation is an active layer property, independent of oxygen and moisture.
2. The process is entirely reversible and related to change in recombination center DENSITY at
D-A interface
3. Follows a non linear DOS pattern with light intensity which is an excellent match with
previous work on both in-organic and organic solar cells.
Regarding Solutions...
Glass + ITO
Polymer cell
a-Si Cell
Efficient tandem structure – ( with >7% efficiency)
59. 59
Future work..
1. Injecting controlled oxygen in the degradation chamber and see the effect of oxygen in
addition to light.
2. Studying the effect of fullerene in the photo-degradation process.
3. Understanding the effect of cathode material on photo-degradation.
4. Photo-induced structural changes in the active layer with the help of Auger
microscopy, XPS, XRD technique.
5. Studying degradation of new polymer system with higher efficiency like PTB7 etc.
6. Studying photo-degradation on hybrid tandem junction solar cells.
60. 60
Sincerely thanks to my advisor Dr. Vikram Dalal for giving me opportunity to
work under his guidance on the OPV project.
To my team mates Bob Mayer, Mehran Samiee , Pranav Joshi & Balaji
Ganapathy
Thanks to Max Noack and Bob Mayer for setting up the degradation chamber
and for many encouraging discussion.
Thanks to my family and friends & all students with whom I worked at MRC.
Acknowledgement
61. 61
2010
R. Biswas, J.Bhattacharya , B.Lewis , N.Chakravarty , V.Dalal- Solar Energy Materials & Solar Cells 94
(2010)2337–2342-“ Enhanced nano crystalline silicon solar cell with a photonic crystal back-reflector”.
2011
J Bhattacharya, N Chakravarty, S Pattnaik, W. D Slafer, R Biswas and V L. Dalal- APPLIED PHYSICS
LETTERS 99, 131114 (2011)-“ A photonic-plasmonic structure for enhancing light absorption in thin film
solar cells”.
2012
J. Bhattacharya, N. Chakravarty , S. Pattnaik , W.D. Slafer , R. Biswas ,V. Dalal- In Press - Journal of Non-
Crystalline Solids-2012. “Comparison of optical properties of periodic photonic–plasmonic and randomly
textured back reflectors for nc-Si solar cells”.
2012
J. Bhattacharya, R. W. Mayer, M. Samiee, and V. L. Dalal –“Appl. Phys. Lett. 100, 193501 (2012)” –“Photo-
induced changes in fundamental properties of organic solar cells”.
List of Selected Publications