Samsung has set a goal of applying transparent PI substrates to its foldable mobile phones by 2024, replacing the currently used yellow PI substrates. The camera takes sharper pictures. Samsung Display has set a goal of applying transparent polyimide (PI) substrates to foldable mobile phones to be released around 2024. The current mass-produced flexible organic light-emitting diodes for foldable mobile phone applications ( OLED) use a yellow PI substrate.
The reason why Samsung Display plans to apply transparent PI substrates to flexible OLEDs is to improve the light transmittance of the under-screen camera (UPC). The lens aperture of the UPC, which is only visible when using the camera function, is structurally located below the OLED display. When using the UPC's camera function, external light must pass through the flexible OLED.
Samsung Display reduced the pixel density of the UPC area to 187 PPI, which is half of the 374 PPI (pixels per inch) of the remaining display area, to make up for these shortcomings brought by the first UPC applied to the Samsung Galaxy Z Fold3. If the pixel density is low, the area that can receive light can be increased. But the display pixel size of the UPC area is also increased to 4 times the remaining area, so there is a clear boundary between the UPC and the rest of the display.
If Samsung Display replaces the yellow PI substrate with a transparent PI substrate as planned, the light transmittance in the UPC area will increase, allowing for sharper pictures than it is now. Pixels can also be packed more densely than they are now, with less noticeable borders from the rest of the display.
The report also said that the heat resistance and high cost of transparent PI varnishes required to produce transparent PI substrates are a challenge. Samsung Display initially wanted to use a transparent PI substrate on the Galaxy Z Fold 3 released last year, but the application was delayed due to the properties of the transparent PI varnish. If Samsung Display successfully develops a transparent PI substrate, it is expected to be applied to Samsung Electronics' foldable mobile phone OLED first, and then to Apple's iPhone.
LG Display is also developing transparent PI substrates for UPC applications according to its own technology roadmap. LG Display's iPhone flexible OLED panels for Apple also use yellow PI substrates. According to the roadmap, LG Display plans to increase the UPC transmittance to 20% by 2023 and 40% after 2024.
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