Organic Photodiode

Organic Photodiodes

(i.e., Image sensor consists of a large number of photodiodes as a form of array.)

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Polymer Electronic Materials Lab

Organic Photodiodes

In imaging devices such as cameras or camcorders, image sensors are used to convert the incident light which is reflected from the subject to electrical signal.

Photodiodes are the unit device of image sensor.

(i.e., Image sensor consists of a large number of photodiodes as a form of array.)

Since Si has indirect band gap, Si can't distinguish the color of incident light. Therefore, color-filters are required to distinguish the color for Si-based photodiodes.

However, since the transmittance of color-filter is not a zero, color-filter can absorb incident photons and it not only leads to the decrease of quantum efficiency of photodiode, but also limits the lens design for image sensor application.

Moreover, Si has low absorption coefficient (< 10 cm ) for visible light and therefore, thick active layer (> 1 μm) is needed for sufficient absorption of photons.

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Organic semiconductor can be fascinating alternative because of its high absorption coefficient (~ 10 cm ) and superior processability (spin or spray coating, inkjet printing, etc.).

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Moreover, by molecular engineering such as the control of π-conjugation length and/or optimization of molecular orientation, the absorption range of organic semiconductors can be changed to have a selectivity to specific color range (R/G/B).

However, to fabricate the conventional organic photodetectors, the absorption spectrums of donor and acceptor materials should coincide and this method can be applied only for green-selection and is practically impossible for blue- and red-selection.

To overcome this drawback, we introduced the concept of "Non-absorbing acceptor", which is a compound word of "non-absorbing" and "electron acceptor".

Non-absorbing acceptor is the electron acceptor which hardly absorbs the visible light (400 - 700 nm).

By using non-absorbing acceptor with color-selective donor, the absorption spectrum of donor material can be fully reflected on the sensing spectrum of the final photodetector.

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SITEMAP

Organic Photodiodes

In imaging devices such as cameras or camcorders, image sensors are used to convert the incident light which is reflected from the subject to electrical signal.

​Photodiodes are the unit device of image sensor.

(i.e., Image sensor consists of a large number of photodiodes as a form of array.)

Since Si has indirect band gap, Si can't distinguish the color of incident light. Therefore, color-filters are required to distinguish the color for Si-based photodiodes.

However, since the transmittance of color-filter is not a zero, color-filter can absorb incident photons and it not only leads to the decrease of quantum efficiency of photodiode, but also limits the lens design for image sensor application.

Moreover, Si has low absorption coefficient (< 10 cm ) for visible light and therefore, thick active layer (> 1 μm) is needed for sufficient absorption of photons.

4

-1

Organic semiconductor can be fascinating alternative because of its high absorption coefficient (~ 10 cm ) and superior processability (spin or spray coating, inkjet printing, etc.).

5

-1

Moreover, by molecular engineering such as the control of π-conjugation length and/or optimization of molecular orientation, the absorption range of organic semiconductors can be changed to have a selectivity to specific color range (R/G/B).

However, to fabricate the conventional organic photodetectors, the absorption spectrums of donor and acceptor materials should coincide and this method can be applied only for green-selection and is practically impossible for blue- and red-selection.

To overcome this drawback, we introduced the concept of "Non-absorbing acceptor", which is a compound word of "non-absorbing" and "electron acceptor".

Non-absorbing acceptor is the electron acceptor which hardly absorbs the visible light (400 - 700 nm).

By using non-absorbing acceptor with color-selective donor, the absorption spectrum of donor material can be fully reflected on the sensing spectrum of the final photodetector.

Photodiodes are the unit device of image sensor.