[ODCAD]Philips-High Effcient Polymer OLED
Improvement of power efficiency is critical for success of OLED display technology. Scientists from Philips claims that a breakthrough in that aspect has been made.
One development Philips made is using proper hole transportation layer (HTL) material. Usually, conductive polymer has more hole injected than electron, which results in waste of energy from extra hole. Choosing proper HTL material to reduce the hole injected can improve the power efficiency. (Sounds like anode junction barrier is increased) The quantum efficiency has been raised to 12% that is about 3 to 6 times higher than standard OLED devices.
Another development Philips made is dispersing a phosphorescent guest material into a light emitting polymer host. The polymer host used by Philips is carbazole-oxadiazole derivative. The guest material is iridium complex. A research fellow Meulenkamp from Philips presented the work on April 28, 2004 at the International Society for Optical Engineering's Photonics Europe conference in Strasbourg, France. Philips expects that these developments can significantly improve polymer OLED (PLED) device performance.
Copy right owned by OD Software Incorporated (ODSI)(http://www.odcad.com/)-the expert and toolkit provider of electronic material, device
Tuesday, April 27, 2004
[ODCAD] Charge Carrier Mobility and Future of Organic Semiconductor
This is comment about Eugen's reply of "Organic TFT Transistor:
Interface and Performance". Regarding the future of organic device,
Eugen is right. From science aspect, there is no
reason to stop this semiconductor technology to replace Si.
In the article "Organic TFT Transistor: Interface and Performance",
ODCAD does mention that there is one issue that is low
mobility of charge carrier. This doe not mean this kind of material
Cannot reach high mobility. As mentioned in the article, it is due to
disorder of the material structure, this is particularly true for
polymer semiconductor. However, once the engineers and scientists
know how to deposit the organic semiconductor in the way that the
material is good order. The mobility will not be issue at all.
One example to prove this is material C6 nanotube. No any adult, it
is organic. The carbon in the material is very ordered due to the
sigma bond. The conjugated p orbital of the carbon form excellent
conduction channel. Its charge carrier mobility is much higher than
all metal material because the charge carrier does have much less
chance to hit the carbon (electron-phonon interaction, plus the other
effect).
Overall, organic semiconductor has great future. At the current
technology level, it is already taking over Si technology in some
areas such as TFT, LED etc.
ODCAD from OD Software Incorporated (ODSI)(http://www.odcad.com/)-the expert and toolkit provider of electronic material, device
This is comment about Eugen's reply of "Organic TFT Transistor:
Interface and Performance". Regarding the future of organic device,
Eugen is right. From science aspect, there is no
reason to stop this semiconductor technology to replace Si.
In the article "Organic TFT Transistor: Interface and Performance",
ODCAD does mention that there is one issue that is low
mobility of charge carrier. This doe not mean this kind of material
Cannot reach high mobility. As mentioned in the article, it is due to
disorder of the material structure, this is particularly true for
polymer semiconductor. However, once the engineers and scientists
know how to deposit the organic semiconductor in the way that the
material is good order. The mobility will not be issue at all.
One example to prove this is material C6 nanotube. No any adult, it
is organic. The carbon in the material is very ordered due to the
sigma bond. The conjugated p orbital of the carbon form excellent
conduction channel. Its charge carrier mobility is much higher than
all metal material because the charge carrier does have much less
chance to hit the carbon (electron-phonon interaction, plus the other
effect).
Overall, organic semiconductor has great future. At the current
technology level, it is already taking over Si technology in some
areas such as TFT, LED etc.
ODCAD from OD Software Incorporated (ODSI)(http://www.odcad.com/)-the expert and toolkit provider of electronic material, device
Tuesday, April 20, 2004
[ODCAD] OLED Color tuned by External Voltage
Achieving multi color OLED device is a challenge task. One approach is to use multi layered structure. The simple one is a five layer structure which are Cathode, Red emissive layer, Green emissive layer, Blue emissive layer, and Anode layer.
One important fact to be used is that the charge carrier mobility is field effect. Usually, higher field, larger mobility. This is more effective for electron as charge carrier in organic semiconductor. Charge carrier mobility decides where hole from anode combines with the electron from the cathode in OLED device along the direction of field. This charge recombination may result in emitting light. Making use of the fact of the mobility effected by field, One can control charge recombination region by adjusting the field strength (voltage applied). As an example, a Red layer is close to the cathode layer. Applying relatively low voltage can result in lower electron mobility compared with hole. This leads to charge recombine at Red layer resulting in Red emitting light. In the same way, one can achieve different color by applying proper voltage.
For accurate control, engineer has to model or simulate the device performance (device simulation) to decide the thickness of each layer, external voltage applied for a specific color, etc.
Copy right owned by OD Software Incorporated (ODSI)-the expert and tool kit provider of electronic material, device
Achieving multi color OLED device is a challenge task. One approach is to use multi layered structure. The simple one is a five layer structure which are Cathode, Red emissive layer, Green emissive layer, Blue emissive layer, and Anode layer.
One important fact to be used is that the charge carrier mobility is field effect. Usually, higher field, larger mobility. This is more effective for electron as charge carrier in organic semiconductor. Charge carrier mobility decides where hole from anode combines with the electron from the cathode in OLED device along the direction of field. This charge recombination may result in emitting light. Making use of the fact of the mobility effected by field, One can control charge recombination region by adjusting the field strength (voltage applied). As an example, a Red layer is close to the cathode layer. Applying relatively low voltage can result in lower electron mobility compared with hole. This leads to charge recombine at Red layer resulting in Red emitting light. In the same way, one can achieve different color by applying proper voltage.
For accurate control, engineer has to model or simulate the device performance (device simulation) to decide the thickness of each layer, external voltage applied for a specific color, etc.
Copy right owned by OD Software Incorporated (ODSI)-the expert and tool kit provider of electronic material, device
[ODCAD] Mobility Effect :Junction of Organic Semiconductor, Electrode
The charge carrier mobility of organic semiconductor is usually much lower than crystal Si material. This low mobility has impact to the transistor (see "Organic TFT Transistor: Interface and Performance"). Also, it has impact to the electrical behavior of the other device.
For a layered structure device, say a simple three layer DIODE device: bottom electrode, middle semiconductor, top electrode. Assume the bottom junction is ohmic, then the diode is due to the top junction. One popular approximate equation is Schottky junction model. The reversed current J0 measured for the junction is usually 6 order (or higher) less than what the model predicts (see "Reversed Current in Schottky Junction"). What is the reason to cause this?
There are quite few reasons for this. One important effect is due to the slow mobility of the charge carrier. A complete model considering charge injection and charge diffusion is Thermionic Emission-Diffusion model (Sze 2nd Edition). In this model, the mobility effect (drift velocity) is trivial if it is large enough compared with thermal charge carrier velocity. Otherwise, the injected current is proportion to the drift velocity that is the product of mobility and field. Dr. Scott from IBM lab in San Jose, CA) has done a set of experiments and the results have confirmed the mobility effect.
This does tell us that the current can be dependent on the mobility even it is at junction control. For device engineer, he (she) has to design (choose) the material to ensure the current obtained from the device can meet the requirements.
Copy right owned by OD Software Incorporated (ODSI)-the expert and tool kit provider of electronic material, device.
The charge carrier mobility of organic semiconductor is usually much lower than crystal Si material. This low mobility has impact to the transistor (see "Organic TFT Transistor: Interface and Performance"). Also, it has impact to the electrical behavior of the other device.
For a layered structure device, say a simple three layer DIODE device: bottom electrode, middle semiconductor, top electrode. Assume the bottom junction is ohmic, then the diode is due to the top junction. One popular approximate equation is Schottky junction model. The reversed current J0 measured for the junction is usually 6 order (or higher) less than what the model predicts (see "Reversed Current in Schottky Junction"). What is the reason to cause this?
There are quite few reasons for this. One important effect is due to the slow mobility of the charge carrier. A complete model considering charge injection and charge diffusion is Thermionic Emission-Diffusion model (Sze 2nd Edition). In this model, the mobility effect (drift velocity) is trivial if it is large enough compared with thermal charge carrier velocity. Otherwise, the injected current is proportion to the drift velocity that is the product of mobility and field. Dr. Scott from IBM lab in San Jose, CA) has done a set of experiments and the results have confirmed the mobility effect.
This does tell us that the current can be dependent on the mobility even it is at junction control. For device engineer, he (she) has to design (choose) the material to ensure the current obtained from the device can meet the requirements.
Copy right owned by OD Software Incorporated (ODSI)-the expert and tool kit provider of electronic material, device.
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