Polymer LED (PLED): Construction, Working, Advantages & Applications

Introduction

Polymers, which are lightweight and flexible, are used as semiconductors in the development of LEDs. A Polymer LED (PLED) is a type of light-emitting diode that uses a polymer material for light generation. PLEDs are used in many applications including automobile lighting, color displays, electronic newspapers, and even bulletproof vests.

PLEDs and polymer photodiodes (PPDs) are considered highly attractive for disposable lab-on-chip applications.
Organic diodes are extremely efficient: their light output can reach up to 20 mW/cm², and photodiodes can achieve an external quantum efficiency above 70%. The peak wavelength of PLEDs can be tuned over the visible spectrum by chemically modifying the emitting polymer. PLEDs are ultra-thin (around 500 nm), compatible with flexible substrates, and can be fabricated at room temperature using additive printing techniques. This allows easy integration into many compact electronic systems.

What Does Polymer LED (PLED) Mean?

A Polymer LED is a type of OLED that uses electroluminescent polymers as the semiconducting layer, creating extremely thin and lightweight LEDs suitable for flexible displays, indoor lighting, and medical technologies such as lab-on-chip illumination. In a PLED, electroluminescent polymers are sandwiched between a transparent anode and a metal cathode. PLEDs are also known as PolyLEDs or Light-Emitting Polymers (LEP).

Compared to conventional inorganic LEDs, polymer LEDs are easier and cheaper to manufacture. Inorganic materials require vacuum processing and special handling—especially for blue LEDs—whereas polymer emitters can be applied using dip coating, spin coating, roll-to-roll processes, and inkjet printing.

Despite their advantages, PLEDs face challenges such as lower durability, color shifting (especially in blue emitters), and sensitivity to oxygen. Proper encapsulation is required to prevent degradation.

Polymer LED Construction

The structure of a Polymer LED is similar to that of a traditional OLED, except that one of the layers is a polymer.
The basic structure includes:

• Cathode
• Polymer emissive layer
• Transparent anode
• Substrate

When external voltage is applied, the polymer emits light. Common polymers used include poly(p-phenylene vinylene) (PPV) and polyfluorene. Refer to OLED working to understand the underlying emission process.

How OLED Works?

OLEDs consist of a cathode, emissive layer, conductive layer, anode, and substrate. The working process is as follows:

1. Voltage is applied from an external power source.
2. Current flows through the organic layers from cathode to anode.
3. Electrons move from the conductive layer to the emissive layer.
4. Holes in the emissive layer are filled by these electrons.
5. When electrons recombine with holes, excess energy is released as light.

This recombination process creates light emission in OLED and PLED devices.

Advantages

• Highly efficient with low power consumption
• Lightweight construction
• Flexible and ultra-thin
• Operates over a wide temperature range
• Wide viewing angle
• Fast response time
• Soft and comfortable brightness
• Low manufacturing cost
• High contrast
• Can be used as a large-area emitter with various shapes

Disadvantages

• The polymer emitter is sensitive to oxygen and moisture
• Color shift occurs due to different lifetimes of polymers (especially blue)
• Shorter lifespan at high brightness levels

Applications

• Displays in mobile phones, laptops, televisions, and advertising screens
• General lighting applications
• Automobile interior and exterior lighting
• Protective vests
• Electronic newspapers (e-paper)