A quasi-ordered bulk heterojunction of P3HT/PCBM solar cells fabricated by zone-casting

In this paper, a quasi-ordered bulk hetertojunction of P3HT/PCBM solar cells (Q-O BHJ device) was fabricated by zone-casting from the solutions with different aging times. P3HT nanofibers aligned in an oriented manner due to the shear stress and solute concentration gradient during zone-casting process. The orientation degree of P3HT nanofibers increased when the aging time of solution was prolonged. Meanwhile, P3HT had a high crystallinity due to the slow evaporation rate of solvent during the film-forming process. The oriented alignment of nanofibers could facilitate the connection between nanofibers by increasing the bridging chains. Furthermore, the bridging chains tended to adopt an untwisted conformation, which results in a reduced energy barrier of hole transfer. As a consequence, the Q-O BHJ device had a higher fill factor (FF) and short-circuit current density (Jsc) compared with the device fabricated by spin coating (BHJ device), leading to an increase by almost more than 50% in device efficiency and a PCE of 3.26% without any annealing treatment.