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

Abstract

Nanofi bers consisting of the bulk heterojunction organic photovoltaic (BHJ-OPV) electron donor-electron acceptor pair poly(3-hexylthiophene):phenyl-C 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.

The Dawn of Single Material Organic Solar Cells

“…[70] In further investigations of the synthesis and structure of the diblock copolymers, the same authors have synthesized P3HT-based diblock copolymers with controllable block lengths by combining Grignard metathesis and nickel-catalyzed quasiliving polymerization. [74] Under AM 1.5 simulated solar light, a SMOSC of 6.25 mm 2 based on 5 gives after thermal treatment a PCE of 3.50%, similar to that obtained with a reference two-component BHJ cell P3HT-PC 61 BM. The UVvis absorption spectra of the copolymers in chloroform were practically identical to that of a 1.0:0.6 weight ratio of a mixture of P3HT:PC 61 BM.…”

Dual Drug Release Electrospun Core-Shell Nanofibers with Tunable Dose in the Second Phase

“…Coaxial electrospinning, in which a concentric spinneret can accommodate two liquids, is regarded as one of the most significant breakthroughs in this area [7–9]. The traditional concept about coaxial electrospinning is that “the shell solution is critical and the selected shell polymer-solvent system should be electrospinnable by itself to facilitate core–shell structure formation, whereas the core solution can either be electrospinnable or not” [10].…”

Electrospun Organic Nanofiber Electronics and Photonics

“…Poly(3‐hexylthiophene) (P3HT) is one of the most typical semiconducting polymers which has been actively studying in ONF electronics 21, 23, 33–41. However, commonly used P3HTs cannot provide enough chain entanglement and cannot overcome Rayleigh instability due to their rigid molecular structure33 and relatively low MWs (19.4 kDa ≤ $\overline {M} _{{\rm w}} $ ≤ 87 kDa) 36–41.…”

“…OPVs have been attracting huge attention in the field of photovoltaics as inexpensive, lightweight, and solution‐processable solar cells that can be compatible with flexible substrates 61–69. Unlike OLEDs, ONFs are largely incorporated in OPVs by diverse preparation methods (e.g., self‐assembled polymer nanowires grown from thin films and fabricated via nanolithography, and ONFs fabricated directly via electrospinning) to increase the power conversion efficiency (PCE) of OPVs 21, 23, 33, 34, 70, 71. ONFs have many strong points in OPVs, such as huge surface‐to‐volume ratio, large exciton diffusion length, easy morphology control, and high charge carrier mobilities 7, 61, 62.…”