Ordered microstructure induced by orientation behavior of liquid-crystal polythiophene for performance improvement of hybrid solar cells

Control of the nanoscale morphology or microstructure of the active layer in hybrid solar cells is critical to ensure the high device performance. Here, a novel electron-donor material, liquid-crystalline polythiophene containing a cyano-biphenyl mesogenic pendant, poly[3-(6-(4-cynaobiphenyloxy)-hexyl) thiophene] (P3HbpT), was rationally designed and synthesized. The spontaneous orientation of cyano-biphenyl mesogen endowed the P3HbpT with a well ordered morphology and facilitated the homogeneous dispersion of ZnO nanoparticles in the composites. The P3HbpT/ZnO composite films exhibited a red-shift absorption (12 nm), the lower LUMO and more ordered domains after undergoing annealing at liquid crystal (LC) states temperature (175 °C), which indicated that the spontaneous assembly behavior of the liquid-crystalline polythiophene could induce the ZnO nanoparticles to form nano-dispersing structure with highly oriented channel layers upon heating at liquid crystalline states. Furthermore, the hybrid bulk-heterojunction devices based on P3HbpT/ZnO active layer have been constructed. Without extensive optimization, the devices undergoing annealing at LC state yielded a Voc of 0.83 V and power conversion efficiency (PCE) of 0.61%, showing a significantly increased Jsc and FF with respect to the un-annealed counterpart.