Novel Phosphazenium Tetrafluoroborate Dopant Enables Efficient and Thermally Stable n‐Doped Organic Semiconductors

<jats:title>Abstract</jats:title><jats:p>Thermal stability is crucial for doped organic semiconductors (OSCs) and their applications in organic thermoelectric (OTE) devices. However, the capacity of n‐dopants to produce thermally stable n‐doped OSC films has not been thoroughly explored, with few reports of high thermal stability. Here, a novel n‐dopant, phosphazenium tetrafluoroborate (P<jats:sub>2</jats:sub>BF<jats:sub>4</jats:sub>) is introduced, which effectively induces n‐doping in N2200, P(PzDPP‐CT2) and several other commonly used OSCs. Remarkably, the electrical conductivity of P<jats:sub>2</jats:sub>BF<jats:sub>4</jats:sub>‐doped OSC films remains almost unchanged even after heating at temperatures &gt; 150 °C for 24 h, far superior to the films doped with benchmark N‐DMBI. The exceptional thermal stability observed in P<jats:sub>2</jats:sub>BF<jats:sub>4</jats:sub>‐doped P(PzDPP‐CT2) films allows for stable operation of the corresponding organic thermoelectric devices at 150 °C for 16 h, a milestone not previously achieved. This study offers valuable insights into the development of n‐dopants capable of producing OSCs with outstanding thermal stability, paving the way for the practical realization of OTE devices with enhanced operation stability.</jats:p>