Fig. 1. Exploration of stable crystal structures of conjugated polymers. (a) Schematic illustration of the exploration strategy to identify multiband hyperbolic dispersion materials. (b) Chemical structures of D-A copolymers comprising T and BT, along with their derivatives. (c) Schematic representation of various polymer configurations, aimed at identifying stable crystal structures for each of the conjugated polymers. (d) Implemented configurations of PTBT as proposed in panel (c). (e) Calculated polymerization energies of various types of PTBT, shown as an example.

Fig. 2. HDs of crystal structures of conjugated polymers. (a) Schematic representation of the stacking structure of PCPDTVBT. (b) Calculated complex permittivity and FOM [$\mathrm{FOM}=-\mathrm{Re}({\epsilon }_H)/\mathrm{Im}({\epsilon }_H)$] for PCPDTVBT. On the right, the equifrequency contours are shown for the dispersion relation of PCPDTVBT at wavelengths of 1000, 550, and 400 nm. (c) FOMs for all considered conjugated polymers, including P3HT as reference.

Fig. 3. Influence of bridge and spacer units on the HDs in copolymers. Band structure, PDOSs of the carbon atoms, and calculated complex permittivity of (a) PDTBT, (b) PCPDTBT, (c) PCPDTEBT, and (d) PCPDTVBT. The gray, red, blue, and green regions in the structure represent the carbon atoms constituting BT, T, the bridge, and the spacers, respectively.

Fig. 4. FDTD simulations of light propagation in OHM films. Tightly focused beams propagating through 100-nm-thick (a)–(c) PCPDTEBT and (d)–(f) PCPDTVBT films. The simulations were conducted for normal-incidence plane waves passing through a 20-nm-wide Cr slit at wavelengths corresponding to the three highest material FOMs, as shown in Fig. 2(c).

Fig. 5. Comparison of modified HDs of oligomer structures with polymer structures. (a) Unit cell of PTBT polymer structure and PTBT oligomer structure defined by an arbitrary effective conjugation length. (b) Differences in the calculated band gaps between polymer and oligomer structures for each conjugated polymer. (c) FOMs of oligomer structures for all conjugated polymers.