Risk of cost increase taken
One of the reasons why Apple employed an OLED panel for the iPhone X's display is probably the process of cutting out the U-shaped part.
"The process of cutting out a U-shaped part is easy with a flexible OLED panel but difficult with an LCD panel using a glass substrate," said Jyunzo Masuda, representative of Insight Resources Display, who is well-versed in the trends in the display industry.
As for OLED panels, flexible OLED panels that use thin, soft polyimide resin are being produced in large quantity. On the other hand, the supply of flexible LCD panels is still limited.
The process of cutting out a U-shaped part is highly likely to cause cost increase because the number of elements that lower yield increases. The elements include the influence of the heat of a laser device used for the process and the ingress of water from a cut surface.
It has been a while since the iPhone X was released, several people in the display industry still say that the yield rate of OLED panels is still low. Others point out that the yield rate is so low that the amount of orders for materials drastically increased.
Complicated design of driving circuit
It takes long to design an OLED panel that has round corners, U-shaped cutout, etc. It is because, with such odd-shaped parts, the number of items that need to be considered at the time of designing the panel's driving circuit increases.