Nanofiber‐Based Bulk‐Heterojunction Organic Solar Cells Using Coaxial Electrospinning

Nanofi bers consisting of the bulk heterojunction organic photovoltaic (BHJ‐ OPV) electron donor‐electron acceptor pair poly(3-hexylthiophene):phenylC 61 -butyric acid methyl ester (P3HT:PCBM) are produced through a coaxial electrospinning process. While P3HT:PCBM blends are not directly electrospinnable, P3HT:PCBM-containing fi bers are produced in a coaxial fashion by utilizing polycaprolactone (PCL) as an electrospinnable sheath material. Pure P3HT:PCBM fi bers are easily obtained after electrospinning by selectively removing the PCL sheath with cyclopentanone (average diameter 120 ± 30 nm). These fi bers are then incorporated into the active layer of a BHJ‐OPV device, which results in improved short-circuit current densities, fi ll factors, and power-conversion effi ciencies (PCE) as compared to thin-fi lm devices of identical chemical composition. The best-performing fi ber-based devices exhibit a PCE of 4.0%, while the best thin-fi lm devices have a PCE of 3.2%. This increase in device performance is attributed to the increased in-plane alignment of P3HT polymer chains on the nanoscale, caused by the electrospun fi bers, which leads to increased optical absorption and subsequent exciton generation. This methodology for improving device performance of BHJ‐OPVs could also be implemented for other electron donor‐electron acceptor systems, as nanofi ber formation is largely independent of the PV material.