Lecture 10. 麻省理工有机光电子课件

FIGURES OF MERRIT:
Power conversion efficiency Full solar intensities Reliability
Consume power to detect a signal
Photodetectors
FIGURES OF MERRIT:
High external quantum efficiency High bandwidth Low noise, low power consumption
POWER SUPPLIES TURBO PUMP COLD TRAP
thickness monitor shutter
substrate
source boats
ROUGHING PUMP
VACUUM CHAMBER
GND
6
History and Progress
‘86: Heterojunction Solar Cell
13
Broad Spectral Response Matches Solar Spectrum
Solar Spectrum AM1.5 30
4
η INTERNAL
3
20
η EXTERNAL
10
light trapping
2
1
0 400
0
600
800Байду номын сангаас
1000
λ [nm]
Photon Flux [1018 s-1 m-2nm-1]
I-V Response under Varying Solar Illumination Intensity
ISC [mA/cm2] VOC [V] Optical power [# suns] (AM1.5 spectrum) 0.1 1 10 100 10 linear 1 0.6 0.5 0.4 0.6 0.5 0.4 0.3 1.2 1.0 0.8 0.6
20.0
90Å CuPc/ 90Å PTCBI
2 19 64 200
VMAX VOC
Current [mA/cm2]
0.0
-20.0 620
IMAX ISC
-40.0
-60.0
960 1300 mW/cm2 = 17 suns (AM1.5)
-80.0
-0.4
-0.2
0.0
0.2
0.4
0.6
15
Voltage [V]
C.W. Tang
Tang, Appl Phys Lett. 48, 183 (1986).
• first heterojunction for efficient charge generation • ~0.95% conversion efficiency • nearly ideal IVs (FF~0.65) • under full solar illumination (1 sun)
60Å CuPc/ 60Å PTCBI
light trapping configuration
Power Conversion Efficiency [%]
3.0 2.5 2.0 Ag aperture Glass Substrate ITO / Organic Layers Ag cathode
7
Photoinduced Charge-Transfer
Processes occuring at a Donor-Acceptor heterojunction
LUMO
1
2
3
4
1 Exciton generation by
absorption of light
2 Exciton diffusion over ~LD 4 3 Exciton dissociation by
Photovoltaics and Photodetectors - part II
• Organic Heterojunction Photovoltaic Cell • Organic Multilayer Photodetector
Data on Solar Cells and Photodetectors taken from Peumans, Bulovic, and Forrest., Appl. Phys. Lett. 76, 2650 (2000) – solar cell Appl. Phys. Lett. 76, 3855 (2000) - photodetector
3 Current [mA/cm2] 2 1 0 -1 -2 -3
Ag PTCBI (500Å) CuPc (300Å) ITO Glass
VOC = 450mV
η = 0.95%
ISC = 2.3mA/cm 2
ff = 0.65
‘90s: Polymer Networks
-0.4 G. Yu et al., Science 270, 1789 (1995). • series resistance problem (low FF) • calculated power conversion efficiency of ~1.5% • not well matched to solar spectrum
10
Exciton Blocking Layer (EBL)
• conducts electrons • transparent • effectively blocks excitons • absorbs damage • separates active layers from metal
BCP
0.0 0 40 80 120 160
LPTCBI [Angstrom]
9
PTCBI
CuPc
Double Heterojunction
Problem
Ag
Solution
Ag EBL
ITO
~200Å
ITO
•cathode metal diffusion Introduce ‘Exciton Blocking •deposition damage Layer’ (EBL) to: •exciton-plasmon interaction •confine excitons to active region •vanishing optical field •act as a damage-absorber •electrical shorts
30 25 20 15 10 5
>2.5-fold improvement in efficiency η INTERNAL
w/ EBL
Previous best devices (Tang, ‘86) η EXTERNAL
no EBL
0
100
200
400
800
CuPc and PTCBI Layer Thickness [Å]
@ MIT
March 11, 2003 – Organic Optoelectronics - Lecture 10
1
Organic Heterojunction PVs
V
VB LD
LD CB
Incident Light
2
Optical power ⇒ electrical power
Photovoltaics
-0.2
0.0
0.2
0.4
Voltage [V]
Shaheen et al. , Appl. Phys. Lett. 78, 841 (2001). • power conversion efficiency ~2.5% • not well matched to solar spectrum • long term stability ?
20 15 10 5 0
Laboratory Production
Po lySi
s-S i
[%]
ta llin eSi
Am o
Or ga nic
Cr ys
rph ou
5
Device Preparation and Growth
substrate holder • Glass substrates precoated with ITO - 94% transparent - 15 Ω/square • Precleaning Tergitol, TCE Acetone, 2-Propanol • Growth - 5 x 10-7 Torr - Room T - 20 to 2000 Å layer thickness
monotonic increase
ηP [%]
FF
no drastic decrease
broad plateau
10 100 1000 Optical power [mW/cm2] (AM1.5 spectrum)
16
Light Trapping Improves PV Efficiency ~2.5 Fold
1.0
540nm
PL efficiency ratio η
0.8
0.6
⎡1 − exp −2 ⋅ PL L ⎢ η = 1 = 1− D ⋅ ⎣ PL2 t ⎡1 + exp −2 ⋅ ⎢ ⎣
PL1
PTCBI
LD=(30±3)Å
0.4
( (
t
)⎤⎥⎦ L ⎤ t L )⎥ ⎦
D D
PL2
0.2
experiment theory
HOMO rapid and efficient charge transfer