TADF stands for Thermally Activated Delayed Fluorescence. It is a phenomenon in which certain organic materials exhibit delayed fluorescence after absorbing light energy. TADF is a key concept in the field of organic light-emitting diodes (OLEDs) and has gained significant attention due to its potential in improving the efficiency of OLED devices.

1. TADF
THERMALLY ACTIVATED DELAYED FLUORESCENCE

2. What is TADF
TADF stands for Thermally Activated Delayed Fluorescence. It is a phenomenon in
which certain organic materials exhibit delayed fluorescence after absorbing light
energy. TADF is a key concept in the field of organic light-emitting diodes (OLEDs)
and has gained significant attention due to its potential in improving the efficiency
of OLED devices.
In OLEDs, electrons and holes recombine in the emissive layer, leading to the
emission of light. However, not all excitons (electron-hole pairs) directly emit light;
some are formed in a non-emissive state. In conventional OLEDs, these non-
emissive excitons are typically lost as heat, limiting the device efficiency.

3. Use of TADF
TADF materials are designed to efficiently harvest these non-emissive excitons.
When these materials are exposed to an appropriate energy level, usually via
electrical or optical excitation, the non-emissive excitons are transformed into
emissive excitons through a thermally activated process. This means that the non-
emissive excitons can be converted into light-emitting excitons at a later time,
leading to delayed fluorescence.
TADF OLEDs have the potential to overcome the limitations of conventional OLEDs
and significantly improve their efficiency. By harvesting both singlet and triplet
excitons, TADF materials can achieve internal quantum efficiencies close to 100%,
making them highly attractive for various display and lighting applications.
The field of TADF research is still actively evolving, and scientists and engineers
continue to explore new TADF materials and device architectures to unlock even
more efficient and brighter OLED technologies.

4. How to harvest the energy
u Harvesting energy refers to the process of capturing and converting
various forms of energy from the environment into usable electrical power.
The methods for energy harvesting can vary depending on the specific
type of energy being harnessed. Here are some common approaches to
harvest different types of energy:

5. How to harvest the energy
u Solar Energy Harvesting:
• Photovoltaic (PV) Cells: Use solar panels made of semiconductor materials to convert sunlight into electricity. PV cells
are commonly used for solar power generation in residential, commercial, and industrial applications.
• Solar Thermal Systems: Use mirrors or lenses to concentrate sunlight onto a receiver to produce heat and then convert it
into electricity through turbines or other thermal-to-electric energy conversion methods.
u Mechanical Energy Harvesting:
• Piezoelectric Devices: Utilize materials that generate electrical charge when subjected to mechanical stress or
vibrations. These devices can convert mechanical movements, such as vibrations or pressure, into electrical energy.
• Electromagnetic Induction: Employ coils and magnets to generate electricity when subjected to mechanical motion.
Common examples include generators in wind turbines and some portable electronic devices that use hand-cranking
or motion-based charging.
u Thermal Energy Harvesting:
• Thermoelectric Generators: Convert temperature differences into electricity using thermoelectric materials. When one
side of the material is heated, and the other side is cooled, a voltage potential is created, leading to electricity
generation.
u Radio Frequency (RF) Energy Harvesting:
• RF Harvesters: Capture and convert ambient radio frequency signals, such as Wi-Fi, cellular signals, or other wireless
transmissions, into electrical energy. RF harvesters can power low-energy devices like sensors and small electronics.

6. Why we use TADF
u Improved Efficiency: TADF materials enable more efficient OLED devices compared to
traditional fluorescent and phosphorescent materials. TADF can harness both singlet and
triplet excitons, which leads to a near 100% internal quantum efficiency. This means that
almost all the electrically generated excitons can be converted into light emission,
resulting in higher brightness and lower power consumption.
u Lower Cost: TADF OLEDs can be manufactured using simpler and potentially more cost-
effective processes compared to phosphorescent OLEDs. Phosphorescent OLEDs often
require expensive and rare heavy-metal-based materials to achieve high efficiency,
while TADF materials are based on organic compounds, which can be more readily
available and cost-efficient.
u Longer Device Lifetime: TADF OLEDs have shown potential for longer operational lifetimes
due to the suppression of exciton quenching, which is a process that reduces the
emission efficiency over time. This improved stability contributes to the longevity of the
OLED devices, making them more reliable and durable.

7. Why we use TADF
u Compatibility with Solution Processing: TADF materials can be processed using
solution-based techniques, such as inkjet printing or roll-to-roll printing. This
compatibility with solution processing methods allows for large-scale and cost-
effective manufacturing, making TADF OLEDs promising for various
applications.
u Design Flexibility: TADF materials offer a wide range of tunability, allowing for
the design of OLEDs with different emission colors, spectral characteristics, and
optoelectronic properties. This flexibility opens up possibilities for creating
custom displays and lighting applications.
u Environmental Benefits: TADF OLEDs based on organic compounds are more
environmentally friendly compared to traditional OLEDs that use heavy metals.
Reducing reliance on rare and potentially harmful materials in electronic
devices can contribute to more sustainable technology development.

8. OLED Fabrication
u Fabricating an OLED (Organic Light-Emitting Diode) involves creating a series of layers containing organic materials and electrodes. The fabrication process
can be quite intricate and typically involves various deposition techniques to form these layers. Here's a general overview of the steps involved in OLED
fabrication:
1. Substrate Preparation:
1. Start with a clean glass or plastic substrate, which will serve as the base for the OLED device.
2. Transparent Electrode Deposition:
1. Deposit a transparent and conductive layer, usually made of indium tin oxide (ITO), onto the substrate using techniques like sputtering or evaporation. This layer will act
as the anode, and it allows light to pass through.
3. Organic Layer Deposition:
1. Apply organic layers to the substrate. These layers include: a. Hole Transport Layer (HTL): A layer that facilitates the flow of positive charge carriers (holes) from the
anode to the emissive layer. b. Emissive Layer: This is the core of the OLED, containing the organic materials that emit light when excited by electrons and holes. c.
Electron Transport Layer (ETL): A layer that facilitates the flow of negative charge carriers (electrons) from the cathode to the emissive layer.
u Cathode Deposition:
• Deposit a cathode layer on top of the organic layers using techniques like thermal evaporation. The cathode is typically made of metals like calcium,
aluminum, or lithium fluoride, which efficiently inject electrons into the emissive layer.
u Encapsulation:
• To protect the organic layers from moisture and oxygen, seal the OLED structure with an encapsulation layer. This layer can be composed of glass or flexible
barrier films.
u Testing and Quality Control:
• After fabrication, each OLED device is tested to ensure functionality and quality. Various parameters, such as luminance, color purity, and operational
lifetime, are evaluated.