According to the latest rumors, Apple has made an order to Samsung for 100 million 5.5" OLED panels in 2017. The displays are supposedly going to make their way to the 2017 iPhone Plus. The timing for the order indicates that the OLED screens will skip the iPhone 7 and only make it to the iPhone 7S.
The information comes from a source cited by the Chinese edition of the WSJ and it also points out that Samsung has set aside a production line at its Asan plant for the order. While the information about future iPhone models using a Samsung-made OLED panel is not new, it was previously anticipated to happen in 2018, not a year earlier.
KGI's analyst Ming-Chi Kuo, who has a mixed track record regarding Apple rumors, also shares similar information. However, he is quite certain that the 2017 iPhone Plus will have a 5.8" display.
The reason for Apple's decision to go OLED could be because currently, its production cost is lower than LCD's. It'll be also interesting to see if rumors surface regarding Apple issuing a request to LG to manufacture OLED panels as a fallback. Up until now, the Korean company has been a key Apple partner in making panels for the iPhone.