Reversible Dopant-Induced Cross-Linking of Semiconducting Polymer Films for Sequential Multilayer Deposition.

Sequential multilayer processing has become increasingly important for the fabrication of semiconducting polymer (SP) devices. For organic light-emitting diodes, photovoltaics (OPVs), and field-effect transistors (OECTs), reducing the energy gap between the transport layer in the SP and the electrode material is critical for optimized devices. Bulk heterojunctions in OPVs suffer from dark charge transport, while planar heterojunctions offer greater control and optimization of interfaces, enabling directional charge transport. Multilayer OPVs are also more mechanically and thermally stable with less dependence on processing conditions. Presented here is a method for preparing multilayers of SPs from solution using sequentially deposited molecular dopants to render the underlayer(s) insoluble. The SP film is temporarily cross-linked by the dopant. Next, a second SP film is deposited from solution. Finally, the doped conjugated polymer undergoes quantitative dedoping, resulting in the complete removal of the dopant from the bilayer. This multi-step processing method can be universally applied to unaltered SPs, resulting in unmixed planar heterojunctions between the SPs. Deposition of p/n, p/p, n/p, and n/n bilayers is demonstrated using multiple different molecular dopants and SPs. The ease, reliability, reproducibility, and materials universality of this processing method will make it valuable for organic electronics research.