Sintered thermoelectric (TE) nanoparticle films are known to have a high figure-of-merit ZT factor and are considered for waste hear recovery and heating and cooling applications. The conventional process of thermal sintering of TE nanoparticles requires an inert environment and long heating times, and cannot be used on polymer substrates due to the requirements of the process (e.g., heating up to 400 °C). In this communication, the authors demonstrate for the first time the use of an intense flash of UV light from a Xenon lamp to sinter TE nanoparticles within milliseconds under ambient conditions on flexible polymer as well as glass substrates to create functional TE films. Photonic sintering is used to fabricate Bismuth Telluride thermoelectric films with a conductivity of 3200 S m−1 (a 5-6 orders of magnitude increase over unsintered films) and a peak power factor of 30 µW m−1 K−2. Modeling is used to gain an insight into the physical processes occurring during photonic sintering process and identify the critical parameters controlling the process. This work opens-up an exciting possibility of extremely rapid fabrication of TE generators under ambient conditions on a variety of flexible and rigid substrates.