# How an OLED makes light

> A graphical abstract of an organic light-emitting diode: holes and electrons step in from the electrodes over a ladder of HOMO and LUMO levels, cross the transport layers of an exploded pixel stack and meet in the emissive layer. There they pair up as one singlet for every three triplet excitons, and fluorescent, phosphorescent or TADF emitters decide how many of them become light. A live 3D pixel and a live 3D rubrene molecule can be turned in the figure.

- Page: https://www.labcanvas.com/templates/graphical-abstracts/how-oled-makes-light
- Open in the LabCanvas editor (LabCanvas account): https://www.labcanvas.com/editor.html?template=how-an-oled-makes-light
- Updated: 2026-10-14
- Category: Materials graphical abstracts
- Method: Graphical abstract
- Starting materials: A glass substrate coated with a transparent ITO anode, organic transport and emissive layers and a metal cathode
- Product: Light leaving the pixel through the ITO and the glass
- Key result: Singlet : triplet = 1 : 3 and internal quantum efficiency ≤25 % (fluorescent) vs up to 100 % (phosphorescent, TADF) (Uoyama 2012; Bui 2018; Luo 2019); TADF OLED external efficiency >19 % (Uoyama 2012); ≈20 % of the light escapes a conventional bottom-emitting OLED (Luo 2019)
- Figure: 1920 × 1080 px, 245 editable layers (2 generated objects with settings)

## Steps

1. **Inject**: Holes enter from the ITO anode and electrons from the metal cathode; small energy steps between adjacent layers keep the driving voltage low (Bui 2018).
2. **Transport and block**: Hole- and electron-transport layers carry each charge to the emissive layer and block the opposite one (Sudheendran Swayamprabha 2020).
3. **Recombine**: Holes and electrons meet in the emissive layer and form singlet and triplet excitons in a 1:3 ratio (Uoyama 2012).
4. **Harvest**: Fluorescent emitters use only singlets (≤25 % internal efficiency); phosphorescent Ir/Pt complexes and TADF molecules turn triplets into light too (up to 100 %).
5. **Light out**: Light leaves through the ITO and glass; in a plain bottom-emitting stack only about 20 % escapes, the rest stays trapped in the glass, the ITO/organic layers and the metal (Luo 2019).

## Uses

- Graphical abstracts on OLEDs and organic emitters
- Teaching device physics of organic semiconductors
- Talks and posters on displays and lighting

## References

1. Uoyama, Goushi, Shizu, Nomura & Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence”, Nature 2012. https://doi.org/10.1038/nature11687 (primary)
2. Luo, Chen, Liu & Qiu, “Emergence of Flexible White Organic Light-Emitting Diodes”, Polymers 2019. https://doi.org/10.3390/polym11020384 (review)
3. Bui, Goubard, Ibrahim-Ouali, Gigmes & Dumur, “Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)”, Beilstein J. Org. Chem. 2018. https://doi.org/10.3762/bjoc.14.18 (review)
4. Cebrián & Mauro, “Recent advances in phosphorescent platinum complexes for organic light-emitting diodes”, Beilstein J. Org. Chem. 2018. https://doi.org/10.3762/bjoc.14.124 (review)
5. Sudheendran Swayamprabha, Dubey, Shahnawaz, Yadav, Nagar, Sharma, Tung & Jou, “Approaches for Long Lifetime Organic Light Emitting Diodes”, Adv. Sci. 2020. https://doi.org/10.1002/advs.202002254 (review)
6. Baldo, Thompson & Forrest, “High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer”, Nature 2000. https://doi.org/10.1038/35001541 (further reading)

Credit: Drawn by LabCanvas after Uoyama et al., Nature 2012 (doi:10.1038/nature11687), Luo et al., Polymers 2019 (doi:10.3390/polym11020384), Bui et al., Beilstein J. Org. Chem. 2018 (doi:10.3762/bjoc.14.18), Cebrián & Mauro, Beilstein J. Org. Chem. 2018 (doi:10.3762/bjoc.14.124) and Sudheendran Swayamprabha et al., Adv. Sci. 2020 (doi:10.1002/advs.202002254). Energy levels schematic.

## Questions

**What does the “How an OLED makes light” template show?** A graphical abstract of an organic light-emitting diode: holes and electrons step in from the electrodes over a ladder of HOMO and LUMO levels, cross the transport layers of an exploded pixel stack and meet in the emissive layer. There they pair up as one singlet for every three triplet excitons, and fluorescent, phosphorescent or TADF emitters decide how many of them become light. A live 3D pixel and a live 3D rubrene molecule can be turned in the figure.

**What are the steps shown in “How an OLED makes light”?** 1. Inject: Holes enter from the ITO anode and electrons from the metal cathode; small energy steps between adjacent layers keep the driving voltage low (Bui 2018). 2. Transport and block: Hole- and electron-transport layers carry each charge to the emissive layer and block the opposite one (Sudheendran Swayamprabha 2020). 3. Recombine: Holes and electrons meet in the emissive layer and form singlet and triplet excitons in a 1:3 ratio (Uoyama 2012). 4. Harvest: Fluorescent emitters use only singlets (≤25 % internal efficiency); phosphorescent Ir/Pt complexes and TADF molecules turn triplets into light too (up to 100 %). 5. Light out: Light leaves through the ITO and glass; in a plain bottom-emitting stack only about 20 % escapes, the rest stays trapped in the glass, the ITO/organic layers and the metal (Luo 2019).

**What are the starting materials and the product?** Starting materials: A glass substrate coated with a transparent ITO anode, organic transport and emissive layers and a metal cathode. Product: Light leaving the pixel through the ITO and the glass.

**Which papers is “How an OLED makes light” based on?** Uoyama, Goushi, Shizu, Nomura & Adachi, “Highly efficient organic light-emitting diodes from delayed fluorescence”, Nature 2012 (doi:10.1038/nature11687); Luo, Chen, Liu & Qiu, “Emergence of Flexible White Organic Light-Emitting Diodes”, Polymers 2019 (doi:10.3390/polym11020384); Bui, Goubard, Ibrahim-Ouali, Gigmes & Dumur, “Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)”, Beilstein J. Org. Chem. 2018 (doi:10.3762/bjoc.14.18); Cebrián & Mauro, “Recent advances in phosphorescent platinum complexes for organic light-emitting diodes”, Beilstein J. Org. Chem. 2018 (doi:10.3762/bjoc.14.124); Sudheendran Swayamprabha, Dubey, Shahnawaz, Yadav, Nagar, Sharma, Tung & Jou, “Approaches for Long Lifetime Organic Light Emitting Diodes”, Adv. Sci. 2020 (doi:10.1002/advs.202002254); Baldo, Thompson & Forrest, “High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer”, Nature 2000 (doi:10.1038/35001541).

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