Lighting the Way: Precision Doping in Organic Semiconductors
Doping is essential for modulating semiconductor conductivity, forming p–n junctions, and reducing contact resistance. However, organic semiconductors (OSCs) face challenges in achieving precise regional doping due to uncontrollable dopant diffusion and poor process compatibility. This highlight discusses a breakthrough light-triggered strategy for spatially controlled n-type doping in OSCs, developed by Pei's Group. The method employs inert photoactivable dopants (iPADs) that are thermally stable but undergo rapid 6π-electrocyclization upon UV irradiation, transforming into potent n-dopants (PADs). These PADs irreversibly dope n-type OSCs via hydride transfer. With a high activation barrier (>28 kcal mol−1), the reaction is thermally suppressed even at 120°C, enabling orthogonal control: doping occurs only where and when light is applied. This approach achieves down to 1 μm spatial resolution, far surpassing physical masking methods. The method's universality accommodates diverse n-type OSCs (LUMO: −3.7 to −4.7 eV) with conductivity enhancements up to nine orders of magnitude (exceeding 30 S cm−1 in some systems). Doping levels, conductivity, and Fermi energy are tunable via UV dose and dopant concentration. The doped regions exhibit robust stability and withstand subsequent thermal processing, aligning with large-scale and flexible manufacturing. In organic field-effect transistors, precise spatial doping significantly enhances carrier mobility, reduces contact resistance to one-sixth of its original value, and effectively lowers surface trap density, providing critical support for device miniaturization and high-density integration.