Highly Efficient Modulation Doping Towards Superior Organic Thermoelectric Devices

Efficient charge generation through doping is key to high performance organic thermoelectric devices. While modulation doping is a widely used doping method in inorganic semiconductors where a heavily doped wide band gap semiconductor is brought in contact with a narrow band gap semiconductor, this technique has not been well studied and exploited in organic semiconductors. Here, we investigate the charge and thermoelectric transport in modulation doped large area rubrene thin-film crystals with different crystal phases. We show that modulation doping allows achieving superior doping efficiencies even for high doping densities, when conventional bulk doping runs into the reserve regime. Modulation-doped orthorhombic rubrene achieve much improved thermoelectric power factors, exceeding 20 µWm-1K-2 at 80 °C. Theoretical simulations provide insights to the energy landscape of the heterostructures and its influence of the qualitative trends of the Seebeck coefficient. Our results show that modulation doping together of high-mobility crystalline organic semiconductor films are a promising strategy for achieving high-performance organic thermoelectrics.