This may be a rumor for now, but the evidence behind it is strong enough to make it highly believable, barring word from Sony. A fan site has pointed out that Sony started releasing their Vita PCH-2000 models right around the time they were ending a partnership with Panasonic to develop OLED technology.
As the report goes, Sony and Panasonic were hoping to make OLED TVs popular to the point that manufacturing costs would go down. They were unable to meet either objective, and decided to end the agreement at the end of 2013.
It’s somewhat odd that Sony would not admit to this, so it may not be entirely true. However, they may simply not be willing to talk about setbacks in their TV and Vita businesses.