Apple has developed the controller for IGZO TFT and OLED sandwich. IGZO tech which is responsible for variable refresh rate on LTPO OLED is developed by JST and so far only two companies have acquired license for it, Sharp and Samsung.
But here is a food for thought. Product Designers have preferred OLED simply because of thinner packaging and less heat emission (I am not counting marketing bait such as battery savings and better image reproduction which all turned to be false one way or another). Now that there is TFT layer in this adaptation screens are becoming thicker again and they emit more heat as well. It would be good to compare state of the art Sharp LCD mobile display with Samsung LTPO OLED and see actual physical specifications.
But here is a food for thought. Product Designers have preferred OLED simply because of thinner packaging and less heat emission (I am not counting marketing bait such as battery savings and better image reproduction which all turned to be false one way or another). Now that there is TFT layer in this adaptation screens are becoming thicker again and they emit more heat as well. It would be good to compare state of the art Sharp LCD mobile display with Samsung LTPO OLED and see actual physical specifications.