1. US Energy Information Administration https://www.eia.gov/tools/faqs/faq.php?id=99&t=3
2. M. Gurman Apple's iPhone X parts cost $115 more than iPhone 8, IHS says https://www.bloomberg.com/news/articles/2017-11-08/apple-s-iphone-x-parts-cost-115-more-than-iphone-8-ihs-says
3. https://www.osram.com/am/services/news/oled-technology-in-the-new-audi-tt-rs/index.jsp