A large area, flexible, OLED assembly has improved thermal management by providing a metal cathode of increased thickness of at least 500 nm. A thermal heat sink trace may be used as alternative or in conjunction with the increased thickness cathode where the trace leads from a central region of the OLED toward a perimeter region, or by other backsheet thermal management designs. External heat sinking, for example to a plate, fixture, etc. may be additionally used or in conjunction with the increased thickness cathode and/or backsheet design to provide further thermal management.